| 1 | |
| 2 | |
| 3 | * RT-Mutexes: simple blocking mutual exclusion locks with PI support
|
| 4 | *
|
| 5 | * started by Ingo Molnar and Thomas Gleixner.
|
| 6 | *
|
| 7 | * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <[email protected]>
|
| 8 | * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <[email protected]>
|
| 9 | * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
|
| 10 | * Copyright (C) 2006 Esben Nielsen
|
| 11 | * Adaptive Spinlocks:
|
| 12 | * Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
|
| 13 | * and Peter Morreale,
|
| 14 | * Adaptive Spinlocks simplification:
|
| 15 | * Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <[email protected]>
|
| 16 | *
|
| 17 | * See Documentation/locking/rt-mutex-design.rst for details.
|
| 18 |
|
| 19 | #include <linux/sched.h>
|
| 20 | #include <linux/sched/debug.h>
|
| 21 | #include <linux/sched/deadline.h>
|
| 22 | #include <linux/sched/signal.h>
|
| 23 | #include <linux/sched/rt.h>
|
| 24 | #include <linux/sched/wake_q.h>
|
| 25 | #include <linux/ww_mutex.h>
|
| 26 |
|
| 27 | #include <trace/events/lock.h>
|
| 28 |
|
| 29 | #include "rtmutex_common.h"
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| 30 |
|
| 31 | #ifndef WW_RT
|
| 32 | # define build_ww_mutex() (false)
|
| 33 | # define ww_container_of(rtm) NULL
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| 34 |
|
| 35 | static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
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| 36 | struct rt_mutex *lock,
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| 37 | struct ww_acquire_ctx *ww_ctx)
|
| 38 | {
|
| 39 | return 0;
|
| 40 | }
|
| 41 |
|
| 42 | static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
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| 43 | struct ww_acquire_ctx *ww_ctx)
|
| 44 | {
|
| 45 | }
|
| 46 |
|
| 47 | static inline void ww_mutex_lock_acquired(struct ww_mutex *lock,
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| 48 | struct ww_acquire_ctx *ww_ctx)
|
| 49 | {
|
| 50 | }
|
| 51 |
|
| 52 | static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
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| 53 | struct rt_mutex_waiter *waiter,
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| 54 | struct ww_acquire_ctx *ww_ctx)
|
| 55 | {
|
| 56 | return 0;
|
| 57 | }
|
| 58 |
|
| 59 | #else
|
| 60 | # define build_ww_mutex() (true)
|
| 61 | # define ww_container_of(rtm) container_of(rtm, struct ww_mutex, base)
|
| 62 | # include "ww_mutex.h"
|
| 63 | #endif
|
| 64 |
|
| 65 | |
| 66 | * lock->owner state tracking:
|
| 67 | *
|
| 68 | * lock->owner holds the task_struct pointer of the owner. Bit 0
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| 69 | * is used to keep track of the "lock has waiters" state.
|
| 70 | *
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| 71 | * owner bit0
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| 72 | * NULL 0 lock is free (fast acquire possible)
|
| 73 | * NULL 1 lock is free and has waiters and the top waiter
|
| 74 | * is going to take the lock*
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| 75 | * taskpointer 0 lock is held (fast release possible)
|
| 76 | * taskpointer 1 lock is held and has waiters**
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| 77 | *
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| 78 | * The fast atomic compare exchange based acquire and release is only
|
| 79 | * possible when bit 0 of lock->owner is 0.
|
| 80 | *
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| 81 | * (*) It also can be a transitional state when grabbing the lock
|
| 82 | * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
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| 83 | * we need to set the bit0 before looking at the lock, and the owner may be
|
| 84 | * NULL in this small time, hence this can be a transitional state.
|
| 85 | *
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| 86 | * (**) There is a small time when bit 0 is set but there are no
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| 87 | * waiters. This can happen when grabbing the lock in the slow path.
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| 88 | * To prevent a cmpxchg of the owner releasing the lock, we need to
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| 89 | * set this bit before looking at the lock.
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| 90 |
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| 91 |
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| 92 | static __always_inline struct task_struct *
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| 93 | rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner)
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| 94 | {
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| 95 | unsigned long val = (unsigned long)owner;
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| 96 |
|
| 97 | if (rt_mutex_has_waiters(lock))
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| 98 | val |= RT_MUTEX_HAS_WAITERS;
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| 99 |
|
| 100 | return (struct task_struct *)val;
|
| 101 | }
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| 102 |
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| 103 | static __always_inline void
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| 104 | rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
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| 105 | {
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| 106 | |
| 107 | * lock->wait_lock is held but explicit acquire semantics are needed
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| 108 | * for a new lock owner so WRITE_ONCE is insufficient.
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| 109 |
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| 110 | xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner));
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| 111 | }
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| 112 |
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| 113 | static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock)
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| 114 | {
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| 115 |
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| 116 | WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL));
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| 117 | }
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| 118 |
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| 119 | static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
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| 120 | {
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| 121 | lock->owner = (struct task_struct *)
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| 122 | ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
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| 123 | }
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| 124 |
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| 125 | static __always_inline void
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| 126 | fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock)
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| 127 | {
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| 128 | unsigned long owner, *p = (unsigned long *) &lock->owner;
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| 129 |
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| 130 | if (rt_mutex_has_waiters(lock))
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| 131 | return;
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| 132 |
|
| 133 | |
| 134 | * The rbtree has no waiters enqueued, now make sure that the
|
| 135 | * lock->owner still has the waiters bit set, otherwise the
|
| 136 | * following can happen:
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| 137 | *
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| 138 | * CPU 0 CPU 1 CPU2
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| 139 | * l->owner=T1
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| 140 | * rt_mutex_lock(l)
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| 141 | * lock(l->lock)
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| 142 | * l->owner = T1 | HAS_WAITERS;
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| 143 | * enqueue(T2)
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| 144 | * boost()
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| 145 | * unlock(l->lock)
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| 146 | * block()
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| 147 | *
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| 148 | * rt_mutex_lock(l)
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| 149 | * lock(l->lock)
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| 150 | * l->owner = T1 | HAS_WAITERS;
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| 151 | * enqueue(T3)
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| 152 | * boost()
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| 153 | * unlock(l->lock)
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| 154 | * block()
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| 155 | * signal(->T2) signal(->T3)
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| 156 | * lock(l->lock)
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| 157 | * dequeue(T2)
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| 158 | * deboost()
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| 159 | * unlock(l->lock)
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| 160 | * lock(l->lock)
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| 161 | * dequeue(T3)
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| 162 | * ==> wait list is empty
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| 163 | * deboost()
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| 164 | * unlock(l->lock)
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| 165 | * lock(l->lock)
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| 166 | * fixup_rt_mutex_waiters()
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| 167 | * if (wait_list_empty(l) {
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| 168 | * l->owner = owner
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| 169 | * owner = l->owner & ~HAS_WAITERS;
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| 170 | * ==> l->owner = T1
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| 171 | * }
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| 172 | * lock(l->lock)
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| 173 | * rt_mutex_unlock(l) fixup_rt_mutex_waiters()
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| 174 | * if (wait_list_empty(l) {
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| 175 | * owner = l->owner & ~HAS_WAITERS;
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| 176 | * cmpxchg(l->owner, T1, NULL)
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| 177 | * ===> Success (l->owner = NULL)
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| 178 | *
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| 179 | * l->owner = owner
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| 180 | * ==> l->owner = T1
|
| 181 | * }
|
| 182 | *
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| 183 | * With the check for the waiter bit in place T3 on CPU2 will not
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| 184 | * overwrite. All tasks fiddling with the waiters bit are
|
| 185 | * serialized by l->lock, so nothing else can modify the waiters
|
| 186 | * bit. If the bit is set then nothing can change l->owner either
|
| 187 | * so the simple RMW is safe. The cmpxchg() will simply fail if it
|
| 188 | * happens in the middle of the RMW because the waiters bit is
|
| 189 | * still set.
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| 190 |
|
| 191 | owner = READ_ONCE(*p);
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| 192 | if (owner & RT_MUTEX_HAS_WAITERS) {
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| 193 | |
| 194 | * See rt_mutex_set_owner() and rt_mutex_clear_owner() on
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| 195 | * why xchg_acquire() is used for updating owner for
|
| 196 | * locking and WRITE_ONCE() for unlocking.
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| 197 | *
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| 198 | * WRITE_ONCE() would work for the acquire case too, but
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| 199 | * in case that the lock acquisition failed it might
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| 200 | * force other lockers into the slow path unnecessarily.
|
| 201 |
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| 202 | if (acquire_lock)
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| 203 | xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS);
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| 204 | else
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| 205 | WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
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| 206 | }
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| 207 | }
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| 208 |
|
| 209 | |
| 210 | * We can speed up the acquire/release, if there's no debugging state to be
|
| 211 | * set up.
|
| 212 |
|
| 213 | #ifndef CONFIG_DEBUG_RT_MUTEXES
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| 214 | static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
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| 215 | struct task_struct *old,
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| 216 | struct task_struct *new)
|
| 217 | {
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| 218 | return try_cmpxchg_acquire(&lock->owner, &old, new);
|
| 219 | }
|
| 220 |
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| 221 | static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
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| 222 | struct task_struct *old,
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| 223 | struct task_struct *new)
|
| 224 | {
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| 225 | return try_cmpxchg_release(&lock->owner, &old, new);
|
| 226 | }
|
| 227 |
|
| 228 | |
| 229 | * Callers must hold the ->wait_lock -- which is the whole purpose as we force
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| 230 | * all future threads that attempt to [Rmw] the lock to the slowpath. As such
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| 231 | * relaxed semantics suffice.
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| 232 |
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| 233 | static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
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| 234 | {
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| 235 | unsigned long owner, *p = (unsigned long *) &lock->owner;
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| 236 |
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| 237 | do {
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| 238 | owner = *p;
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| 239 | } while (cmpxchg_relaxed(p, owner,
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| 240 | owner | RT_MUTEX_HAS_WAITERS) != owner);
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| 241 |
|
| 242 | |
| 243 | * The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE
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| 244 | * operations in the event of contention. Ensure the successful
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| 245 | * cmpxchg is visible.
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| 246 |
|
| 247 | smp_mb__after_atomic();
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| 248 | }
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| 249 |
|
| 250 | |
| 251 | * Safe fastpath aware unlock:
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| 252 | * 1) Clear the waiters bit
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| 253 | * 2) Drop lock->wait_lock
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| 254 | * 3) Try to unlock the lock with cmpxchg
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| 255 |
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| 256 | static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
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| 257 | unsigned long flags)
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| 258 | __releases(lock->wait_lock)
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| 259 | {
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| 260 | struct task_struct *owner = rt_mutex_owner(lock);
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| 261 |
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| 262 | clear_rt_mutex_waiters(lock);
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| 263 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
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| 264 | |
| 265 | * If a new waiter comes in between the unlock and the cmpxchg
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| 266 | * we have two situations:
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| 267 | *
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| 268 | * unlock(wait_lock);
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| 269 | * lock(wait_lock);
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| 270 | * cmpxchg(p, owner, 0) == owner
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| 271 | * mark_rt_mutex_waiters(lock);
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| 272 | * acquire(lock);
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| 273 | * or:
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| 274 | *
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| 275 | * unlock(wait_lock);
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| 276 | * lock(wait_lock);
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| 277 | * mark_rt_mutex_waiters(lock);
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| 278 | *
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| 279 | * cmpxchg(p, owner, 0) != owner
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| 280 | * enqueue_waiter();
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| 281 | * unlock(wait_lock);
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| 282 | * lock(wait_lock);
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| 283 | * wake waiter();
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| 284 | * unlock(wait_lock);
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| 285 | * lock(wait_lock);
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| 286 | * acquire(lock);
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| 287 |
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| 288 | return rt_mutex_cmpxchg_release(lock, owner, NULL);
|
| 289 | }
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| 290 |
|
| 291 | #else
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| 292 | static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
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| 293 | struct task_struct *old,
|
| 294 | struct task_struct *new)
|
| 295 | {
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| 296 | return false;
|
| 297 |
|
| 298 | }
|
| 299 |
|
| 300 | static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
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| 301 | struct task_struct *old,
|
| 302 | struct task_struct *new)
|
| 303 | {
|
| 304 | return false;
|
| 305 | }
|
| 306 |
|
| 307 | static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
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| 308 | {
|
| 309 | lock->owner = (struct task_struct *)
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| 310 | ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
|
| 311 | }
|
| 312 |
|
| 313 | |
| 314 | * Simple slow path only version: lock->owner is protected by lock->wait_lock.
|
| 315 |
|
| 316 | static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
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| 317 | unsigned long flags)
|
| 318 | __releases(lock->wait_lock)
|
| 319 | {
|
| 320 | lock->owner = NULL;
|
| 321 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
| 322 | return true;
|
| 323 | }
|
| 324 | #endif
|
| 325 |
|
| 326 | static __always_inline int __waiter_prio(struct task_struct *task)
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| 327 | {
|
| 328 | int prio = task->prio;
|
| 329 |
|
| 330 | if (!rt_prio(prio))
|
| 331 | return DEFAULT_PRIO;
|
| 332 |
|
| 333 | return prio;
|
| 334 | }
|
| 335 |
|
| 336 | static __always_inline void
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| 337 | waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
|
| 338 | {
|
| 339 | waiter->prio = __waiter_prio(task);
|
| 340 | waiter->deadline = task->dl.deadline;
|
| 341 | }
|
| 342 |
|
| 343 | |
| 344 | * Only use with rt_mutex_waiter_{less,equal}()
|
| 345 |
|
| 346 | #define task_to_waiter(p) \
|
| 347 | &(struct rt_mutex_waiter){ .prio = __waiter_prio(p), .deadline = (p)->dl.deadline }
|
| 348 |
|
| 349 | static __always_inline int rt_mutex_waiter_less(struct rt_mutex_waiter *left,
|
| 350 | struct rt_mutex_waiter *right)
|
| 351 | {
|
| 352 | if (left->prio < right->prio)
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| 353 | return 1;
|
| 354 |
|
| 355 | |
| 356 | * If both waiters have dl_prio(), we check the deadlines of the
|
| 357 | * associated tasks.
|
| 358 | * If left waiter has a dl_prio(), and we didn't return 1 above,
|
| 359 | * then right waiter has a dl_prio() too.
|
| 360 |
|
| 361 | if (dl_prio(left->prio))
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| 362 | return dl_time_before(left->deadline, right->deadline);
|
| 363 |
|
| 364 | return 0;
|
| 365 | }
|
| 366 |
|
| 367 | static __always_inline int rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
|
| 368 | struct rt_mutex_waiter *right)
|
| 369 | {
|
| 370 | if (left->prio != right->prio)
|
| 371 | return 0;
|
| 372 |
|
| 373 | |
| 374 | * If both waiters have dl_prio(), we check the deadlines of the
|
| 375 | * associated tasks.
|
| 376 | * If left waiter has a dl_prio(), and we didn't return 0 above,
|
| 377 | * then right waiter has a dl_prio() too.
|
| 378 |
|
| 379 | if (dl_prio(left->prio))
|
| 380 | return left->deadline == right->deadline;
|
| 381 |
|
| 382 | return 1;
|
| 383 | }
|
| 384 |
|
| 385 | static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter,
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| 386 | struct rt_mutex_waiter *top_waiter)
|
| 387 | {
|
| 388 | if (rt_mutex_waiter_less(waiter, top_waiter))
|
| 389 | return true;
|
| 390 |
|
| 391 | #ifdef RT_MUTEX_BUILD_SPINLOCKS
|
| 392 | |
| 393 | * Note that RT tasks are excluded from same priority (lateral)
|
| 394 | * steals to prevent the introduction of an unbounded latency.
|
| 395 |
|
| 396 | if (rt_prio(waiter->prio) || dl_prio(waiter->prio))
|
| 397 | return false;
|
| 398 |
|
| 399 | return rt_mutex_waiter_equal(waiter, top_waiter);
|
| 400 | #else
|
| 401 | return false;
|
| 402 | #endif
|
| 403 | }
|
| 404 |
|
| 405 | #define __node_2_waiter(node) \
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| 406 | rb_entry((node), struct rt_mutex_waiter, tree_entry)
|
| 407 |
|
| 408 | static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b)
|
| 409 | {
|
| 410 | struct rt_mutex_waiter *aw = __node_2_waiter(a);
|
| 411 | struct rt_mutex_waiter *bw = __node_2_waiter(b);
|
| 412 |
|
| 413 | if (rt_mutex_waiter_less(aw, bw))
|
| 414 | return 1;
|
| 415 |
|
| 416 | if (!build_ww_mutex())
|
| 417 | return 0;
|
| 418 |
|
| 419 | if (rt_mutex_waiter_less(bw, aw))
|
| 420 | return 0;
|
| 421 |
|
| 422 |
|
| 423 | if (aw->ww_ctx) {
|
| 424 | if (!bw->ww_ctx)
|
| 425 | return 1;
|
| 426 |
|
| 427 | return (signed long)(aw->ww_ctx->stamp -
|
| 428 | bw->ww_ctx->stamp) < 0;
|
| 429 | }
|
| 430 |
|
| 431 | return 0;
|
| 432 | }
|
| 433 |
|
| 434 | static __always_inline void
|
| 435 | rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
|
| 436 | {
|
| 437 | rb_add_cached(&waiter->tree_entry, &lock->waiters, __waiter_less);
|
| 438 | }
|
| 439 |
|
| 440 | static __always_inline void
|
| 441 | rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
|
| 442 | {
|
| 443 | if (RB_EMPTY_NODE(&waiter->tree_entry))
|
| 444 | return;
|
| 445 |
|
| 446 | rb_erase_cached(&waiter->tree_entry, &lock->waiters);
|
| 447 | RB_CLEAR_NODE(&waiter->tree_entry);
|
| 448 | }
|
| 449 |
|
| 450 | #define __node_2_pi_waiter(node) \
|
| 451 | rb_entry((node), struct rt_mutex_waiter, pi_tree_entry)
|
| 452 |
|
| 453 | static __always_inline bool
|
| 454 | __pi_waiter_less(struct rb_node *a, const struct rb_node *b)
|
| 455 | {
|
| 456 | return rt_mutex_waiter_less(__node_2_pi_waiter(a), __node_2_pi_waiter(b));
|
| 457 | }
|
| 458 |
|
| 459 | static __always_inline void
|
| 460 | rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
|
| 461 | {
|
| 462 | rb_add_cached(&waiter->pi_tree_entry, &task->pi_waiters, __pi_waiter_less);
|
| 463 | }
|
| 464 |
|
| 465 | static __always_inline void
|
| 466 | rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
|
| 467 | {
|
| 468 | if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
|
| 469 | return;
|
| 470 |
|
| 471 | rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
|
| 472 | RB_CLEAR_NODE(&waiter->pi_tree_entry);
|
| 473 | }
|
| 474 |
|
| 475 | static __always_inline void rt_mutex_adjust_prio(struct task_struct *p)
|
| 476 | {
|
| 477 | struct task_struct *pi_task = NULL;
|
| 478 |
|
| 479 | lockdep_assert_held(&p->pi_lock);
|
| 480 |
|
| 481 | if (task_has_pi_waiters(p))
|
| 482 | pi_task = task_top_pi_waiter(p)->task;
|
| 483 |
|
| 484 | rt_mutex_setprio(p, pi_task);
|
| 485 | }
|
| 486 |
|
| 487 |
|
| 488 | static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
|
| 489 | struct task_struct *task,
|
| 490 | unsigned int wake_state)
|
| 491 | {
|
| 492 | if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) {
|
| 493 | if (IS_ENABLED(CONFIG_PROVE_LOCKING))
|
| 494 | WARN_ON_ONCE(wqh->rtlock_task);
|
| 495 | get_task_struct(task);
|
| 496 | wqh->rtlock_task = task;
|
| 497 | } else {
|
| 498 | wake_q_add(&wqh->head, task);
|
| 499 | }
|
| 500 | }
|
| 501 |
|
| 502 | static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
|
| 503 | struct rt_mutex_waiter *w)
|
| 504 | {
|
| 505 | rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state);
|
| 506 | }
|
| 507 |
|
| 508 | static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
|
| 509 | {
|
| 510 | if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) {
|
| 511 | wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT);
|
| 512 | put_task_struct(wqh->rtlock_task);
|
| 513 | wqh->rtlock_task = NULL;
|
| 514 | }
|
| 515 |
|
| 516 | if (!wake_q_empty(&wqh->head))
|
| 517 | wake_up_q(&wqh->head);
|
| 518 |
|
| 519 |
|
| 520 | preempt_enable();
|
| 521 | }
|
| 522 |
|
| 523 | |
| 524 | * Deadlock detection is conditional:
|
| 525 | *
|
| 526 | * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
|
| 527 | * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
|
| 528 | *
|
| 529 | * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
|
| 530 | * conducted independent of the detect argument.
|
| 531 | *
|
| 532 | * If the waiter argument is NULL this indicates the deboost path and
|
| 533 | * deadlock detection is disabled independent of the detect argument
|
| 534 | * and the config settings.
|
| 535 |
|
| 536 | static __always_inline bool
|
| 537 | rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
|
| 538 | enum rtmutex_chainwalk chwalk)
|
| 539 | {
|
| 540 | if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
|
| 541 | return waiter != NULL;
|
| 542 | return chwalk == RT_MUTEX_FULL_CHAINWALK;
|
| 543 | }
|
| 544 |
|
| 545 | static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p)
|
| 546 | {
|
| 547 | return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
|
| 548 | }
|
| 549 |
|
| 550 | |
| 551 | * Adjust the priority chain. Also used for deadlock detection.
|
| 552 | * Decreases task's usage by one - may thus free the task.
|
| 553 | *
|
| 554 | * @task: the task owning the mutex (owner) for which a chain walk is
|
| 555 | * probably needed
|
| 556 | * @chwalk: do we have to carry out deadlock detection?
|
| 557 | * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
|
| 558 | * things for a task that has just got its priority adjusted, and
|
| 559 | * is waiting on a mutex)
|
| 560 | * @next_lock: the mutex on which the owner of @orig_lock was blocked before
|
| 561 | * we dropped its pi_lock. Is never dereferenced, only used for
|
| 562 | * comparison to detect lock chain changes.
|
| 563 | * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
|
| 564 | * its priority to the mutex owner (can be NULL in the case
|
| 565 | * depicted above or if the top waiter is gone away and we are
|
| 566 | * actually deboosting the owner)
|
| 567 | * @top_task: the current top waiter
|
| 568 | *
|
| 569 | * Returns 0 or -EDEADLK.
|
| 570 | *
|
| 571 | * Chain walk basics and protection scope
|
| 572 | *
|
| 573 | * [R] refcount on task
|
| 574 | * [P] task->pi_lock held
|
| 575 | * [L] rtmutex->wait_lock held
|
| 576 | *
|
| 577 | * Step Description Protected by
|
| 578 | * function arguments:
|
| 579 | * @task [R]
|
| 580 | * @orig_lock if != NULL @top_task is blocked on it
|
| 581 | * @next_lock Unprotected. Cannot be
|
| 582 | * dereferenced. Only used for
|
| 583 | * comparison.
|
| 584 | * @orig_waiter if != NULL @top_task is blocked on it
|
| 585 | * @top_task current, or in case of proxy
|
| 586 | * locking protected by calling
|
| 587 | * code
|
| 588 | * again:
|
| 589 | * loop_sanity_check();
|
| 590 | * retry:
|
| 591 | * [1] lock(task->pi_lock); [R] acquire [P]
|
| 592 | * [2] waiter = task->pi_blocked_on; [P]
|
| 593 | * [3] check_exit_conditions_1(); [P]
|
| 594 | * [4] lock = waiter->lock; [P]
|
| 595 | * [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
|
| 596 | * unlock(task->pi_lock); release [P]
|
| 597 | * goto retry;
|
| 598 | * }
|
| 599 | * [6] check_exit_conditions_2(); [P] + [L]
|
| 600 | * [7] requeue_lock_waiter(lock, waiter); [P] + [L]
|
| 601 | * [8] unlock(task->pi_lock); release [P]
|
| 602 | * put_task_struct(task); release [R]
|
| 603 | * [9] check_exit_conditions_3(); [L]
|
| 604 | * [10] task = owner(lock); [L]
|
| 605 | * get_task_struct(task); [L] acquire [R]
|
| 606 | * lock(task->pi_lock); [L] acquire [P]
|
| 607 | * [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
|
| 608 | * [12] check_exit_conditions_4(); [P] + [L]
|
| 609 | * [13] unlock(task->pi_lock); release [P]
|
| 610 | * unlock(lock->wait_lock); release [L]
|
| 611 | * goto again;
|
| 612 |
|
| 613 | static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task,
|
| 614 | enum rtmutex_chainwalk chwalk,
|
| 615 | struct rt_mutex_base *orig_lock,
|
| 616 | struct rt_mutex_base *next_lock,
|
| 617 | struct rt_mutex_waiter *orig_waiter,
|
| 618 | struct task_struct *top_task)
|
| 619 | {
|
| 620 | struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
|
| 621 | struct rt_mutex_waiter *prerequeue_top_waiter;
|
| 622 | int ret = 0, depth = 0;
|
| 623 | struct rt_mutex_base *lock;
|
| 624 | bool detect_deadlock;
|
| 625 | bool requeue = true;
|
| 626 |
|
| 627 | detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
|
| 628 |
|
| 629 | |
| 630 | * The (de)boosting is a step by step approach with a lot of
|
| 631 | * pitfalls. We want this to be preemptible and we want hold a
|
| 632 | * maximum of two locks per step. So we have to check
|
| 633 | * carefully whether things change under us.
|
| 634 |
|
| 635 | again:
|
| 636 | |
| 637 | * We limit the lock chain length for each invocation.
|
| 638 |
|
| 639 | if (++depth > max_lock_depth) {
|
| 640 | static int prev_max;
|
| 641 |
|
| 642 | |
| 643 | * Print this only once. If the admin changes the limit,
|
| 644 | * print a new message when reaching the limit again.
|
| 645 |
|
| 646 | if (prev_max != max_lock_depth) {
|
| 647 | prev_max = max_lock_depth;
|
| 648 | printk(KERN_WARNING "Maximum lock depth %d reached "
|
| 649 | "task: %s (%d)\n", max_lock_depth,
|
| 650 | top_task->comm, task_pid_nr(top_task));
|
| 651 | }
|
| 652 | put_task_struct(task);
|
| 653 |
|
| 654 | return -EDEADLK;
|
| 655 | }
|
| 656 |
|
| 657 | |
| 658 | * We are fully preemptible here and only hold the refcount on
|
| 659 | * @task. So everything can have changed under us since the
|
| 660 | * caller or our own code below (goto retry/again) dropped all
|
| 661 | * locks.
|
| 662 |
|
| 663 | retry:
|
| 664 | |
| 665 | * [1] Task cannot go away as we did a get_task() before !
|
| 666 |
|
| 667 | raw_spin_lock_irq(&task->pi_lock);
|
| 668 |
|
| 669 | |
| 670 | * [2] Get the waiter on which @task is blocked on.
|
| 671 |
|
| 672 | waiter = task->pi_blocked_on;
|
| 673 |
|
| 674 | |
| 675 | * [3] check_exit_conditions_1() protected by task->pi_lock.
|
| 676 |
|
| 677 |
|
| 678 | |
| 679 | * Check whether the end of the boosting chain has been
|
| 680 | * reached or the state of the chain has changed while we
|
| 681 | * dropped the locks.
|
| 682 |
|
| 683 | if (!waiter)
|
| 684 | goto out_unlock_pi;
|
| 685 |
|
| 686 | |
| 687 | * Check the orig_waiter state. After we dropped the locks,
|
| 688 | * the previous owner of the lock might have released the lock.
|
| 689 |
|
| 690 | if (orig_waiter && !rt_mutex_owner(orig_lock))
|
| 691 | goto out_unlock_pi;
|
| 692 |
|
| 693 | |
| 694 | * We dropped all locks after taking a refcount on @task, so
|
| 695 | * the task might have moved on in the lock chain or even left
|
| 696 | * the chain completely and blocks now on an unrelated lock or
|
| 697 | * on @orig_lock.
|
| 698 | *
|
| 699 | * We stored the lock on which @task was blocked in @next_lock,
|
| 700 | * so we can detect the chain change.
|
| 701 |
|
| 702 | if (next_lock != waiter->lock)
|
| 703 | goto out_unlock_pi;
|
| 704 |
|
| 705 | |
| 706 | * There could be 'spurious' loops in the lock graph due to ww_mutex,
|
| 707 | * consider:
|
| 708 | *
|
| 709 | * P1: A, ww_A, ww_B
|
| 710 | * P2: ww_B, ww_A
|
| 711 | * P3: A
|
| 712 | *
|
| 713 | * P3 should not return -EDEADLK because it gets trapped in the cycle
|
| 714 | * created by P1 and P2 (which will resolve -- and runs into
|
| 715 | * max_lock_depth above). Therefore disable detect_deadlock such that
|
| 716 | * the below termination condition can trigger once all relevant tasks
|
| 717 | * are boosted.
|
| 718 | *
|
| 719 | * Even when we start with ww_mutex we can disable deadlock detection,
|
| 720 | * since we would supress a ww_mutex induced deadlock at [6] anyway.
|
| 721 | * Supressing it here however is not sufficient since we might still
|
| 722 | * hit [6] due to adjustment driven iteration.
|
| 723 | *
|
| 724 | * NOTE: if someone were to create a deadlock between 2 ww_classes we'd
|
| 725 | * utterly fail to report it; lockdep should.
|
| 726 |
|
| 727 | if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock)
|
| 728 | detect_deadlock = false;
|
| 729 |
|
| 730 | |
| 731 | * Drop out, when the task has no waiters. Note,
|
| 732 | * top_waiter can be NULL, when we are in the deboosting
|
| 733 | * mode!
|
| 734 |
|
| 735 | if (top_waiter) {
|
| 736 | if (!task_has_pi_waiters(task))
|
| 737 | goto out_unlock_pi;
|
| 738 | |
| 739 | * If deadlock detection is off, we stop here if we
|
| 740 | * are not the top pi waiter of the task. If deadlock
|
| 741 | * detection is enabled we continue, but stop the
|
| 742 | * requeueing in the chain walk.
|
| 743 |
|
| 744 | if (top_waiter != task_top_pi_waiter(task)) {
|
| 745 | if (!detect_deadlock)
|
| 746 | goto out_unlock_pi;
|
| 747 | else
|
| 748 | requeue = false;
|
| 749 | }
|
| 750 | }
|
| 751 |
|
| 752 | |
| 753 | * If the waiter priority is the same as the task priority
|
| 754 | * then there is no further priority adjustment necessary. If
|
| 755 | * deadlock detection is off, we stop the chain walk. If its
|
| 756 | * enabled we continue, but stop the requeueing in the chain
|
| 757 | * walk.
|
| 758 |
|
| 759 | if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
|
| 760 | if (!detect_deadlock)
|
| 761 | goto out_unlock_pi;
|
| 762 | else
|
| 763 | requeue = false;
|
| 764 | }
|
| 765 |
|
| 766 | |
| 767 | * [4] Get the next lock
|
| 768 |
|
| 769 | lock = waiter->lock;
|
| 770 | |
| 771 | * [5] We need to trylock here as we are holding task->pi_lock,
|
| 772 | * which is the reverse lock order versus the other rtmutex
|
| 773 | * operations.
|
| 774 |
|
| 775 | if (!raw_spin_trylock(&lock->wait_lock)) {
|
| 776 | raw_spin_unlock_irq(&task->pi_lock);
|
| 777 | cpu_relax();
|
| 778 | goto retry;
|
| 779 | }
|
| 780 |
|
| 781 | |
| 782 | * [6] check_exit_conditions_2() protected by task->pi_lock and
|
| 783 | * lock->wait_lock.
|
| 784 | *
|
| 785 | * Deadlock detection. If the lock is the same as the original
|
| 786 | * lock which caused us to walk the lock chain or if the
|
| 787 | * current lock is owned by the task which initiated the chain
|
| 788 | * walk, we detected a deadlock.
|
| 789 |
|
| 790 | if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
|
| 791 | ret = -EDEADLK;
|
| 792 |
|
| 793 | |
| 794 | * When the deadlock is due to ww_mutex; also see above. Don't
|
| 795 | * report the deadlock and instead let the ww_mutex wound/die
|
| 796 | * logic pick which of the contending threads gets -EDEADLK.
|
| 797 | *
|
| 798 | * NOTE: assumes the cycle only contains a single ww_class; any
|
| 799 | * other configuration and we fail to report; also, see
|
| 800 | * lockdep.
|
| 801 |
|
| 802 | if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx)
|
| 803 | ret = 0;
|
| 804 |
|
| 805 | raw_spin_unlock(&lock->wait_lock);
|
| 806 | goto out_unlock_pi;
|
| 807 | }
|
| 808 |
|
| 809 | |
| 810 | * If we just follow the lock chain for deadlock detection, no
|
| 811 | * need to do all the requeue operations. To avoid a truckload
|
| 812 | * of conditionals around the various places below, just do the
|
| 813 | * minimum chain walk checks.
|
| 814 |
|
| 815 | if (!requeue) {
|
| 816 | |
| 817 | * No requeue[7] here. Just release @task [8]
|
| 818 |
|
| 819 | raw_spin_unlock(&task->pi_lock);
|
| 820 | put_task_struct(task);
|
| 821 |
|
| 822 | |
| 823 | * [9] check_exit_conditions_3 protected by lock->wait_lock.
|
| 824 | * If there is no owner of the lock, end of chain.
|
| 825 |
|
| 826 | if (!rt_mutex_owner(lock)) {
|
| 827 | raw_spin_unlock_irq(&lock->wait_lock);
|
| 828 | return 0;
|
| 829 | }
|
| 830 |
|
| 831 |
|
| 832 | task = get_task_struct(rt_mutex_owner(lock));
|
| 833 | raw_spin_lock(&task->pi_lock);
|
| 834 |
|
| 835 | |
| 836 | * No requeue [11] here. We just do deadlock detection.
|
| 837 | *
|
| 838 | * [12] Store whether owner is blocked
|
| 839 | * itself. Decision is made after dropping the locks
|
| 840 |
|
| 841 | next_lock = task_blocked_on_lock(task);
|
| 842 | |
| 843 | * Get the top waiter for the next iteration
|
| 844 |
|
| 845 | top_waiter = rt_mutex_top_waiter(lock);
|
| 846 |
|
| 847 |
|
| 848 | raw_spin_unlock(&task->pi_lock);
|
| 849 | raw_spin_unlock_irq(&lock->wait_lock);
|
| 850 |
|
| 851 |
|
| 852 | if (!next_lock)
|
| 853 | goto out_put_task;
|
| 854 | goto again;
|
| 855 | }
|
| 856 |
|
| 857 | |
| 858 | * Store the current top waiter before doing the requeue
|
| 859 | * operation on @lock. We need it for the boost/deboost
|
| 860 | * decision below.
|
| 861 |
|
| 862 | prerequeue_top_waiter = rt_mutex_top_waiter(lock);
|
| 863 |
|
| 864 |
|
| 865 | rt_mutex_dequeue(lock, waiter);
|
| 866 |
|
| 867 | |
| 868 | * Update the waiter prio fields now that we're dequeued.
|
| 869 | *
|
| 870 | * These values can have changed through either:
|
| 871 | *
|
| 872 | * sys_sched_set_scheduler() / sys_sched_setattr()
|
| 873 | *
|
| 874 | * or
|
| 875 | *
|
| 876 | * DL CBS enforcement advancing the effective deadline.
|
| 877 | *
|
| 878 | * Even though pi_waiters also uses these fields, and that tree is only
|
| 879 | * updated in [11], we can do this here, since we hold [L], which
|
| 880 | * serializes all pi_waiters access and rb_erase() does not care about
|
| 881 | * the values of the node being removed.
|
| 882 |
|
| 883 | waiter_update_prio(waiter, task);
|
| 884 |
|
| 885 | rt_mutex_enqueue(lock, waiter);
|
| 886 |
|
| 887 |
|
| 888 | raw_spin_unlock(&task->pi_lock);
|
| 889 | put_task_struct(task);
|
| 890 |
|
| 891 | |
| 892 | * [9] check_exit_conditions_3 protected by lock->wait_lock.
|
| 893 | *
|
| 894 | * We must abort the chain walk if there is no lock owner even
|
| 895 | * in the dead lock detection case, as we have nothing to
|
| 896 | * follow here. This is the end of the chain we are walking.
|
| 897 |
|
| 898 | if (!rt_mutex_owner(lock)) {
|
| 899 | |
| 900 | * If the requeue [7] above changed the top waiter,
|
| 901 | * then we need to wake the new top waiter up to try
|
| 902 | * to get the lock.
|
| 903 |
|
| 904 | top_waiter = rt_mutex_top_waiter(lock);
|
| 905 | if (prerequeue_top_waiter != top_waiter)
|
| 906 | wake_up_state(top_waiter->task, top_waiter->wake_state);
|
| 907 | raw_spin_unlock_irq(&lock->wait_lock);
|
| 908 | return 0;
|
| 909 | }
|
| 910 |
|
| 911 |
|
| 912 | task = get_task_struct(rt_mutex_owner(lock));
|
| 913 | raw_spin_lock(&task->pi_lock);
|
| 914 |
|
| 915 |
|
| 916 | if (waiter == rt_mutex_top_waiter(lock)) {
|
| 917 | |
| 918 | * The waiter became the new top (highest priority)
|
| 919 | * waiter on the lock. Replace the previous top waiter
|
| 920 | * in the owner tasks pi waiters tree with this waiter
|
| 921 | * and adjust the priority of the owner.
|
| 922 |
|
| 923 | rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
|
| 924 | rt_mutex_enqueue_pi(task, waiter);
|
| 925 | rt_mutex_adjust_prio(task);
|
| 926 |
|
| 927 | } else if (prerequeue_top_waiter == waiter) {
|
| 928 | |
| 929 | * The waiter was the top waiter on the lock, but is
|
| 930 | * no longer the top priority waiter. Replace waiter in
|
| 931 | * the owner tasks pi waiters tree with the new top
|
| 932 | * (highest priority) waiter and adjust the priority
|
| 933 | * of the owner.
|
| 934 | * The new top waiter is stored in @waiter so that
|
| 935 | * @waiter == @top_waiter evaluates to true below and
|
| 936 | * we continue to deboost the rest of the chain.
|
| 937 |
|
| 938 | rt_mutex_dequeue_pi(task, waiter);
|
| 939 | waiter = rt_mutex_top_waiter(lock);
|
| 940 | rt_mutex_enqueue_pi(task, waiter);
|
| 941 | rt_mutex_adjust_prio(task);
|
| 942 | } else {
|
| 943 | |
| 944 | * Nothing changed. No need to do any priority
|
| 945 | * adjustment.
|
| 946 |
|
| 947 | }
|
| 948 |
|
| 949 | |
| 950 | * [12] check_exit_conditions_4() protected by task->pi_lock
|
| 951 | * and lock->wait_lock. The actual decisions are made after we
|
| 952 | * dropped the locks.
|
| 953 | *
|
| 954 | * Check whether the task which owns the current lock is pi
|
| 955 | * blocked itself. If yes we store a pointer to the lock for
|
| 956 | * the lock chain change detection above. After we dropped
|
| 957 | * task->pi_lock next_lock cannot be dereferenced anymore.
|
| 958 |
|
| 959 | next_lock = task_blocked_on_lock(task);
|
| 960 | |
| 961 | * Store the top waiter of @lock for the end of chain walk
|
| 962 | * decision below.
|
| 963 |
|
| 964 | top_waiter = rt_mutex_top_waiter(lock);
|
| 965 |
|
| 966 |
|
| 967 | raw_spin_unlock(&task->pi_lock);
|
| 968 | raw_spin_unlock_irq(&lock->wait_lock);
|
| 969 |
|
| 970 | |
| 971 | * Make the actual exit decisions [12], based on the stored
|
| 972 | * values.
|
| 973 | *
|
| 974 | * We reached the end of the lock chain. Stop right here. No
|
| 975 | * point to go back just to figure that out.
|
| 976 |
|
| 977 | if (!next_lock)
|
| 978 | goto out_put_task;
|
| 979 |
|
| 980 | |
| 981 | * If the current waiter is not the top waiter on the lock,
|
| 982 | * then we can stop the chain walk here if we are not in full
|
| 983 | * deadlock detection mode.
|
| 984 |
|
| 985 | if (!detect_deadlock && waiter != top_waiter)
|
| 986 | goto out_put_task;
|
| 987 |
|
| 988 | goto again;
|
| 989 |
|
| 990 | out_unlock_pi:
|
| 991 | raw_spin_unlock_irq(&task->pi_lock);
|
| 992 | out_put_task:
|
| 993 | put_task_struct(task);
|
| 994 |
|
| 995 | return ret;
|
| 996 | }
|
| 997 |
|
| 998 | |
| 999 | * Try to take an rt-mutex
|
| 1000 | *
|
| 1001 | * Must be called with lock->wait_lock held and interrupts disabled
|
| 1002 | *
|
| 1003 | * @lock: The lock to be acquired.
|
| 1004 | * @task: The task which wants to acquire the lock
|
| 1005 | * @waiter: The waiter that is queued to the lock's wait tree if the
|
| 1006 | * callsite called task_blocked_on_lock(), otherwise NULL
|
| 1007 |
|
| 1008 | static int __sched
|
| 1009 | try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task,
|
| 1010 | struct rt_mutex_waiter *waiter)
|
| 1011 | {
|
| 1012 | lockdep_assert_held(&lock->wait_lock);
|
| 1013 |
|
| 1014 | |
| 1015 | * Before testing whether we can acquire @lock, we set the
|
| 1016 | * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
|
| 1017 | * other tasks which try to modify @lock into the slow path
|
| 1018 | * and they serialize on @lock->wait_lock.
|
| 1019 | *
|
| 1020 | * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
|
| 1021 | * as explained at the top of this file if and only if:
|
| 1022 | *
|
| 1023 | * - There is a lock owner. The caller must fixup the
|
| 1024 | * transient state if it does a trylock or leaves the lock
|
| 1025 | * function due to a signal or timeout.
|
| 1026 | *
|
| 1027 | * - @task acquires the lock and there are no other
|
| 1028 | * waiters. This is undone in rt_mutex_set_owner(@task) at
|
| 1029 | * the end of this function.
|
| 1030 |
|
| 1031 | mark_rt_mutex_waiters(lock);
|
| 1032 |
|
| 1033 | |
| 1034 | * If @lock has an owner, give up.
|
| 1035 |
|
| 1036 | if (rt_mutex_owner(lock))
|
| 1037 | return 0;
|
| 1038 |
|
| 1039 | |
| 1040 | * If @waiter != NULL, @task has already enqueued the waiter
|
| 1041 | * into @lock waiter tree. If @waiter == NULL then this is a
|
| 1042 | * trylock attempt.
|
| 1043 |
|
| 1044 | if (waiter) {
|
| 1045 | struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock);
|
| 1046 |
|
| 1047 | |
| 1048 | * If waiter is the highest priority waiter of @lock,
|
| 1049 | * or allowed to steal it, take it over.
|
| 1050 |
|
| 1051 | if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter)) {
|
| 1052 | |
| 1053 | * We can acquire the lock. Remove the waiter from the
|
| 1054 | * lock waiters tree.
|
| 1055 |
|
| 1056 | rt_mutex_dequeue(lock, waiter);
|
| 1057 | } else {
|
| 1058 | return 0;
|
| 1059 | }
|
| 1060 | } else {
|
| 1061 | |
| 1062 | * If the lock has waiters already we check whether @task is
|
| 1063 | * eligible to take over the lock.
|
| 1064 | *
|
| 1065 | * If there are no other waiters, @task can acquire
|
| 1066 | * the lock. @task->pi_blocked_on is NULL, so it does
|
| 1067 | * not need to be dequeued.
|
| 1068 |
|
| 1069 | if (rt_mutex_has_waiters(lock)) {
|
| 1070 |
|
| 1071 | if (!rt_mutex_steal(task_to_waiter(task),
|
| 1072 | rt_mutex_top_waiter(lock)))
|
| 1073 | return 0;
|
| 1074 |
|
| 1075 | |
| 1076 | * The current top waiter stays enqueued. We
|
| 1077 | * don't have to change anything in the lock
|
| 1078 | * waiters order.
|
| 1079 |
|
| 1080 | } else {
|
| 1081 | |
| 1082 | * No waiters. Take the lock without the
|
| 1083 | * pi_lock dance.@task->pi_blocked_on is NULL
|
| 1084 | * and we have no waiters to enqueue in @task
|
| 1085 | * pi waiters tree.
|
| 1086 |
|
| 1087 | goto takeit;
|
| 1088 | }
|
| 1089 | }
|
| 1090 |
|
| 1091 | |
| 1092 | * Clear @task->pi_blocked_on. Requires protection by
|
| 1093 | * @task->pi_lock. Redundant operation for the @waiter == NULL
|
| 1094 | * case, but conditionals are more expensive than a redundant
|
| 1095 | * store.
|
| 1096 |
|
| 1097 | raw_spin_lock(&task->pi_lock);
|
| 1098 | task->pi_blocked_on = NULL;
|
| 1099 | |
| 1100 | * Finish the lock acquisition. @task is the new owner. If
|
| 1101 | * other waiters exist we have to insert the highest priority
|
| 1102 | * waiter into @task->pi_waiters tree.
|
| 1103 |
|
| 1104 | if (rt_mutex_has_waiters(lock))
|
| 1105 | rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
|
| 1106 | raw_spin_unlock(&task->pi_lock);
|
| 1107 |
|
| 1108 | takeit:
|
| 1109 | |
| 1110 | * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
|
| 1111 | * are still waiters or clears it.
|
| 1112 |
|
| 1113 | rt_mutex_set_owner(lock, task);
|
| 1114 |
|
| 1115 | return 1;
|
| 1116 | }
|
| 1117 |
|
| 1118 | |
| 1119 | * Task blocks on lock.
|
| 1120 | *
|
| 1121 | * Prepare waiter and propagate pi chain
|
| 1122 | *
|
| 1123 | * This must be called with lock->wait_lock held and interrupts disabled
|
| 1124 |
|
| 1125 | static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
|
| 1126 | struct rt_mutex_waiter *waiter,
|
| 1127 | struct task_struct *task,
|
| 1128 | struct ww_acquire_ctx *ww_ctx,
|
| 1129 | enum rtmutex_chainwalk chwalk)
|
| 1130 | {
|
| 1131 | struct task_struct *owner = rt_mutex_owner(lock);
|
| 1132 | struct rt_mutex_waiter *top_waiter = waiter;
|
| 1133 | struct rt_mutex_base *next_lock;
|
| 1134 | int chain_walk = 0, res;
|
| 1135 |
|
| 1136 | lockdep_assert_held(&lock->wait_lock);
|
| 1137 |
|
| 1138 | |
| 1139 | * Early deadlock detection. We really don't want the task to
|
| 1140 | * enqueue on itself just to untangle the mess later. It's not
|
| 1141 | * only an optimization. We drop the locks, so another waiter
|
| 1142 | * can come in before the chain walk detects the deadlock. So
|
| 1143 | * the other will detect the deadlock and return -EDEADLOCK,
|
| 1144 | * which is wrong, as the other waiter is not in a deadlock
|
| 1145 | * situation.
|
| 1146 | *
|
| 1147 | * Except for ww_mutex, in that case the chain walk must already deal
|
| 1148 | * with spurious cycles, see the comments at [3] and [6].
|
| 1149 |
|
| 1150 | if (owner == task && !(build_ww_mutex() && ww_ctx))
|
| 1151 | return -EDEADLK;
|
| 1152 |
|
| 1153 | raw_spin_lock(&task->pi_lock);
|
| 1154 | waiter->task = task;
|
| 1155 | waiter->lock = lock;
|
| 1156 | waiter_update_prio(waiter, task);
|
| 1157 |
|
| 1158 |
|
| 1159 | if (rt_mutex_has_waiters(lock))
|
| 1160 | top_waiter = rt_mutex_top_waiter(lock);
|
| 1161 | rt_mutex_enqueue(lock, waiter);
|
| 1162 |
|
| 1163 | task->pi_blocked_on = waiter;
|
| 1164 |
|
| 1165 | raw_spin_unlock(&task->pi_lock);
|
| 1166 |
|
| 1167 | if (build_ww_mutex() && ww_ctx) {
|
| 1168 | struct rt_mutex *rtm;
|
| 1169 |
|
| 1170 |
|
| 1171 | rtm = container_of(lock, struct rt_mutex, rtmutex);
|
| 1172 | res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx);
|
| 1173 | if (res) {
|
| 1174 | raw_spin_lock(&task->pi_lock);
|
| 1175 | rt_mutex_dequeue(lock, waiter);
|
| 1176 | task->pi_blocked_on = NULL;
|
| 1177 | raw_spin_unlock(&task->pi_lock);
|
| 1178 | return res;
|
| 1179 | }
|
| 1180 | }
|
| 1181 |
|
| 1182 | if (!owner)
|
| 1183 | return 0;
|
| 1184 |
|
| 1185 | raw_spin_lock(&owner->pi_lock);
|
| 1186 | if (waiter == rt_mutex_top_waiter(lock)) {
|
| 1187 | rt_mutex_dequeue_pi(owner, top_waiter);
|
| 1188 | rt_mutex_enqueue_pi(owner, waiter);
|
| 1189 |
|
| 1190 | rt_mutex_adjust_prio(owner);
|
| 1191 | if (owner->pi_blocked_on)
|
| 1192 | chain_walk = 1;
|
| 1193 | } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
|
| 1194 | chain_walk = 1;
|
| 1195 | }
|
| 1196 |
|
| 1197 |
|
| 1198 | next_lock = task_blocked_on_lock(owner);
|
| 1199 |
|
| 1200 | raw_spin_unlock(&owner->pi_lock);
|
| 1201 | |
| 1202 | * Even if full deadlock detection is on, if the owner is not
|
| 1203 | * blocked itself, we can avoid finding this out in the chain
|
| 1204 | * walk.
|
| 1205 |
|
| 1206 | if (!chain_walk || !next_lock)
|
| 1207 | return 0;
|
| 1208 |
|
| 1209 | |
| 1210 | * The owner can't disappear while holding a lock,
|
| 1211 | * so the owner struct is protected by wait_lock.
|
| 1212 | * Gets dropped in rt_mutex_adjust_prio_chain()!
|
| 1213 |
|
| 1214 | get_task_struct(owner);
|
| 1215 |
|
| 1216 | raw_spin_unlock_irq(&lock->wait_lock);
|
| 1217 |
|
| 1218 | res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
|
| 1219 | next_lock, waiter, task);
|
| 1220 |
|
| 1221 | raw_spin_lock_irq(&lock->wait_lock);
|
| 1222 |
|
| 1223 | return res;
|
| 1224 | }
|
| 1225 |
|
| 1226 | |
| 1227 | * Remove the top waiter from the current tasks pi waiter tree and
|
| 1228 | * queue it up.
|
| 1229 | *
|
| 1230 | * Called with lock->wait_lock held and interrupts disabled.
|
| 1231 |
|
| 1232 | static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
|
| 1233 | struct rt_mutex_base *lock)
|
| 1234 | {
|
| 1235 | struct rt_mutex_waiter *waiter;
|
| 1236 |
|
| 1237 | raw_spin_lock(¤t->pi_lock);
|
| 1238 |
|
| 1239 | waiter = rt_mutex_top_waiter(lock);
|
| 1240 |
|
| 1241 | |
| 1242 | * Remove it from current->pi_waiters and deboost.
|
| 1243 | *
|
| 1244 | * We must in fact deboost here in order to ensure we call
|
| 1245 | * rt_mutex_setprio() to update p->pi_top_task before the
|
| 1246 | * task unblocks.
|
| 1247 |
|
| 1248 | rt_mutex_dequeue_pi(current, waiter);
|
| 1249 | rt_mutex_adjust_prio(current);
|
| 1250 |
|
| 1251 | |
| 1252 | * As we are waking up the top waiter, and the waiter stays
|
| 1253 | * queued on the lock until it gets the lock, this lock
|
| 1254 | * obviously has waiters. Just set the bit here and this has
|
| 1255 | * the added benefit of forcing all new tasks into the
|
| 1256 | * slow path making sure no task of lower priority than
|
| 1257 | * the top waiter can steal this lock.
|
| 1258 |
|
| 1259 | lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
|
| 1260 |
|
| 1261 | |
| 1262 | * We deboosted before waking the top waiter task such that we don't
|
| 1263 | * run two tasks with the 'same' priority (and ensure the
|
| 1264 | * p->pi_top_task pointer points to a blocked task). This however can
|
| 1265 | * lead to priority inversion if we would get preempted after the
|
| 1266 | * deboost but before waking our donor task, hence the preempt_disable()
|
| 1267 | * before unlock.
|
| 1268 | *
|
| 1269 | * Pairs with preempt_enable() in rt_mutex_wake_up_q();
|
| 1270 |
|
| 1271 | preempt_disable();
|
| 1272 | rt_mutex_wake_q_add(wqh, waiter);
|
| 1273 | raw_spin_unlock(¤t->pi_lock);
|
| 1274 | }
|
| 1275 |
|
| 1276 | static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
|
| 1277 | {
|
| 1278 | int ret = try_to_take_rt_mutex(lock, current, NULL);
|
| 1279 |
|
| 1280 | |
| 1281 | * try_to_take_rt_mutex() sets the lock waiters bit
|
| 1282 | * unconditionally. Clean this up.
|
| 1283 |
|
| 1284 | fixup_rt_mutex_waiters(lock, true);
|
| 1285 |
|
| 1286 | return ret;
|
| 1287 | }
|
| 1288 |
|
| 1289 | |
| 1290 | * Slow path try-lock function:
|
| 1291 |
|
| 1292 | static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
|
| 1293 | {
|
| 1294 | unsigned long flags;
|
| 1295 | int ret;
|
| 1296 |
|
| 1297 | |
| 1298 | * If the lock already has an owner we fail to get the lock.
|
| 1299 | * This can be done without taking the @lock->wait_lock as
|
| 1300 | * it is only being read, and this is a trylock anyway.
|
| 1301 |
|
| 1302 | if (rt_mutex_owner(lock))
|
| 1303 | return 0;
|
| 1304 |
|
| 1305 | |
| 1306 | * The mutex has currently no owner. Lock the wait lock and try to
|
| 1307 | * acquire the lock. We use irqsave here to support early boot calls.
|
| 1308 |
|
| 1309 | raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
| 1310 |
|
| 1311 | ret = __rt_mutex_slowtrylock(lock);
|
| 1312 |
|
| 1313 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
| 1314 |
|
| 1315 | return ret;
|
| 1316 | }
|
| 1317 |
|
| 1318 | static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
|
| 1319 | {
|
| 1320 | if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
|
| 1321 | return 1;
|
| 1322 |
|
| 1323 | return rt_mutex_slowtrylock(lock);
|
| 1324 | }
|
| 1325 |
|
| 1326 | |
| 1327 | * Slow path to release a rt-mutex.
|
| 1328 |
|
| 1329 | static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
|
| 1330 | {
|
| 1331 | DEFINE_RT_WAKE_Q(wqh);
|
| 1332 | unsigned long flags;
|
| 1333 |
|
| 1334 |
|
| 1335 | raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
| 1336 |
|
| 1337 | debug_rt_mutex_unlock(lock);
|
| 1338 |
|
| 1339 | |
| 1340 | * We must be careful here if the fast path is enabled. If we
|
| 1341 | * have no waiters queued we cannot set owner to NULL here
|
| 1342 | * because of:
|
| 1343 | *
|
| 1344 | * foo->lock->owner = NULL;
|
| 1345 | * rtmutex_lock(foo->lock); <- fast path
|
| 1346 | * free = atomic_dec_and_test(foo->refcnt);
|
| 1347 | * rtmutex_unlock(foo->lock); <- fast path
|
| 1348 | * if (free)
|
| 1349 | * kfree(foo);
|
| 1350 | * raw_spin_unlock(foo->lock->wait_lock);
|
| 1351 | *
|
| 1352 | * So for the fastpath enabled kernel:
|
| 1353 | *
|
| 1354 | * Nothing can set the waiters bit as long as we hold
|
| 1355 | * lock->wait_lock. So we do the following sequence:
|
| 1356 | *
|
| 1357 | * owner = rt_mutex_owner(lock);
|
| 1358 | * clear_rt_mutex_waiters(lock);
|
| 1359 | * raw_spin_unlock(&lock->wait_lock);
|
| 1360 | * if (cmpxchg(&lock->owner, owner, 0) == owner)
|
| 1361 | * return;
|
| 1362 | * goto retry;
|
| 1363 | *
|
| 1364 | * The fastpath disabled variant is simple as all access to
|
| 1365 | * lock->owner is serialized by lock->wait_lock:
|
| 1366 | *
|
| 1367 | * lock->owner = NULL;
|
| 1368 | * raw_spin_unlock(&lock->wait_lock);
|
| 1369 |
|
| 1370 | while (!rt_mutex_has_waiters(lock)) {
|
| 1371 |
|
| 1372 | if (unlock_rt_mutex_safe(lock, flags) == true)
|
| 1373 | return;
|
| 1374 |
|
| 1375 | raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
| 1376 | }
|
| 1377 |
|
| 1378 | |
| 1379 | * The wakeup next waiter path does not suffer from the above
|
| 1380 | * race. See the comments there.
|
| 1381 | *
|
| 1382 | * Queue the next waiter for wakeup once we release the wait_lock.
|
| 1383 |
|
| 1384 | mark_wakeup_next_waiter(&wqh, lock);
|
| 1385 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
| 1386 |
|
| 1387 | rt_mutex_wake_up_q(&wqh);
|
| 1388 | }
|
| 1389 |
|
| 1390 | static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
|
| 1391 | {
|
| 1392 | if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
|
| 1393 | return;
|
| 1394 |
|
| 1395 | rt_mutex_slowunlock(lock);
|
| 1396 | }
|
| 1397 |
|
| 1398 | #ifdef CONFIG_SMP
|
| 1399 | static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
|
| 1400 | struct rt_mutex_waiter *waiter,
|
| 1401 | struct task_struct *owner)
|
| 1402 | {
|
| 1403 | bool res = true;
|
| 1404 |
|
| 1405 | rcu_read_lock();
|
| 1406 | for (;;) {
|
| 1407 |
|
| 1408 | if (owner != rt_mutex_owner(lock))
|
| 1409 | break;
|
| 1410 | |
| 1411 | * Ensure that @owner is dereferenced after checking that
|
| 1412 | * the lock owner still matches @owner. If that fails,
|
| 1413 | * @owner might point to freed memory. If it still matches,
|
| 1414 | * the rcu_read_lock() ensures the memory stays valid.
|
| 1415 |
|
| 1416 | barrier();
|
| 1417 | |
| 1418 | * Stop spinning when:
|
| 1419 | * - the lock owner has been scheduled out
|
| 1420 | * - current is not longer the top waiter
|
| 1421 | * - current is requested to reschedule (redundant
|
| 1422 | * for CONFIG_PREEMPT_RCU=y)
|
| 1423 | * - the VCPU on which owner runs is preempted
|
| 1424 |
|
| 1425 | if (!owner_on_cpu(owner) || need_resched() ||
|
| 1426 | !rt_mutex_waiter_is_top_waiter(lock, waiter)) {
|
| 1427 | res = false;
|
| 1428 | break;
|
| 1429 | }
|
| 1430 | cpu_relax();
|
| 1431 | }
|
| 1432 | rcu_read_unlock();
|
| 1433 | return res;
|
| 1434 | }
|
| 1435 | #else
|
| 1436 | static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
|
| 1437 | struct rt_mutex_waiter *waiter,
|
| 1438 | struct task_struct *owner)
|
| 1439 | {
|
| 1440 | return false;
|
| 1441 | }
|
| 1442 | #endif
|
| 1443 |
|
| 1444 | #ifdef RT_MUTEX_BUILD_MUTEX
|
| 1445 | |
| 1446 | * Functions required for:
|
| 1447 | * - rtmutex, futex on all kernels
|
| 1448 | * - mutex and rwsem substitutions on RT kernels
|
| 1449 |
|
| 1450 |
|
| 1451 | |
| 1452 | * Remove a waiter from a lock and give up
|
| 1453 | *
|
| 1454 | * Must be called with lock->wait_lock held and interrupts disabled. It must
|
| 1455 | * have just failed to try_to_take_rt_mutex().
|
| 1456 |
|
| 1457 | static void __sched remove_waiter(struct rt_mutex_base *lock,
|
| 1458 | struct rt_mutex_waiter *waiter)
|
| 1459 | {
|
| 1460 | bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
|
| 1461 | struct task_struct *owner = rt_mutex_owner(lock);
|
| 1462 | struct rt_mutex_base *next_lock;
|
| 1463 |
|
| 1464 | lockdep_assert_held(&lock->wait_lock);
|
| 1465 |
|
| 1466 | raw_spin_lock(¤t->pi_lock);
|
| 1467 | rt_mutex_dequeue(lock, waiter);
|
| 1468 | current->pi_blocked_on = NULL;
|
| 1469 | raw_spin_unlock(¤t->pi_lock);
|
| 1470 |
|
| 1471 | |
| 1472 | * Only update priority if the waiter was the highest priority
|
| 1473 | * waiter of the lock and there is an owner to update.
|
| 1474 |
|
| 1475 | if (!owner || !is_top_waiter)
|
| 1476 | return;
|
| 1477 |
|
| 1478 | raw_spin_lock(&owner->pi_lock);
|
| 1479 |
|
| 1480 | rt_mutex_dequeue_pi(owner, waiter);
|
| 1481 |
|
| 1482 | if (rt_mutex_has_waiters(lock))
|
| 1483 | rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
|
| 1484 |
|
| 1485 | rt_mutex_adjust_prio(owner);
|
| 1486 |
|
| 1487 |
|
| 1488 | next_lock = task_blocked_on_lock(owner);
|
| 1489 |
|
| 1490 | raw_spin_unlock(&owner->pi_lock);
|
| 1491 |
|
| 1492 | |
| 1493 | * Don't walk the chain, if the owner task is not blocked
|
| 1494 | * itself.
|
| 1495 |
|
| 1496 | if (!next_lock)
|
| 1497 | return;
|
| 1498 |
|
| 1499 |
|
| 1500 | get_task_struct(owner);
|
| 1501 |
|
| 1502 | raw_spin_unlock_irq(&lock->wait_lock);
|
| 1503 |
|
| 1504 | rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
|
| 1505 | next_lock, NULL, current);
|
| 1506 |
|
| 1507 | raw_spin_lock_irq(&lock->wait_lock);
|
| 1508 | }
|
| 1509 |
|
| 1510 | |
| 1511 | * rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
|
| 1512 | * @lock: the rt_mutex to take
|
| 1513 | * @ww_ctx: WW mutex context pointer
|
| 1514 | * @state: the state the task should block in (TASK_INTERRUPTIBLE
|
| 1515 | * or TASK_UNINTERRUPTIBLE)
|
| 1516 | * @timeout: the pre-initialized and started timer, or NULL for none
|
| 1517 | * @waiter: the pre-initialized rt_mutex_waiter
|
| 1518 | *
|
| 1519 | * Must be called with lock->wait_lock held and interrupts disabled
|
| 1520 |
|
| 1521 | static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
|
| 1522 | struct ww_acquire_ctx *ww_ctx,
|
| 1523 | unsigned int state,
|
| 1524 | struct hrtimer_sleeper *timeout,
|
| 1525 | struct rt_mutex_waiter *waiter)
|
| 1526 | {
|
| 1527 | struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
|
| 1528 | struct task_struct *owner;
|
| 1529 | int ret = 0;
|
| 1530 |
|
| 1531 | for (;;) {
|
| 1532 |
|
| 1533 | if (try_to_take_rt_mutex(lock, current, waiter))
|
| 1534 | break;
|
| 1535 |
|
| 1536 | if (timeout && !timeout->task) {
|
| 1537 | ret = -ETIMEDOUT;
|
| 1538 | break;
|
| 1539 | }
|
| 1540 | if (signal_pending_state(state, current)) {
|
| 1541 | ret = -EINTR;
|
| 1542 | break;
|
| 1543 | }
|
| 1544 |
|
| 1545 | if (build_ww_mutex() && ww_ctx) {
|
| 1546 | ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx);
|
| 1547 | if (ret)
|
| 1548 | break;
|
| 1549 | }
|
| 1550 |
|
| 1551 | if (waiter == rt_mutex_top_waiter(lock))
|
| 1552 | owner = rt_mutex_owner(lock);
|
| 1553 | else
|
| 1554 | owner = NULL;
|
| 1555 | raw_spin_unlock_irq(&lock->wait_lock);
|
| 1556 |
|
| 1557 | if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner))
|
| 1558 | schedule();
|
| 1559 |
|
| 1560 | raw_spin_lock_irq(&lock->wait_lock);
|
| 1561 | set_current_state(state);
|
| 1562 | }
|
| 1563 |
|
| 1564 | __set_current_state(TASK_RUNNING);
|
| 1565 | return ret;
|
| 1566 | }
|
| 1567 |
|
| 1568 | static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
|
| 1569 | struct rt_mutex_waiter *w)
|
| 1570 | {
|
| 1571 | |
| 1572 | * If the result is not -EDEADLOCK or the caller requested
|
| 1573 | * deadlock detection, nothing to do here.
|
| 1574 |
|
| 1575 | if (res != -EDEADLOCK || detect_deadlock)
|
| 1576 | return;
|
| 1577 |
|
| 1578 | if (build_ww_mutex() && w->ww_ctx)
|
| 1579 | return;
|
| 1580 |
|
| 1581 | |
| 1582 | * Yell loudly and stop the task right here.
|
| 1583 |
|
| 1584 | WARN(1, "rtmutex deadlock detected\n");
|
| 1585 | while (1) {
|
| 1586 | set_current_state(TASK_INTERRUPTIBLE);
|
| 1587 | schedule();
|
| 1588 | }
|
| 1589 | }
|
| 1590 |
|
| 1591 | |
| 1592 | * __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
|
| 1593 | * @lock: The rtmutex to block lock
|
| 1594 | * @ww_ctx: WW mutex context pointer
|
| 1595 | * @state: The task state for sleeping
|
| 1596 | * @chwalk: Indicator whether full or partial chainwalk is requested
|
| 1597 | * @waiter: Initializer waiter for blocking
|
| 1598 |
|
| 1599 | static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
|
| 1600 | struct ww_acquire_ctx *ww_ctx,
|
| 1601 | unsigned int state,
|
| 1602 | enum rtmutex_chainwalk chwalk,
|
| 1603 | struct rt_mutex_waiter *waiter)
|
| 1604 | {
|
| 1605 | struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
|
| 1606 | struct ww_mutex *ww = ww_container_of(rtm);
|
| 1607 | int ret;
|
| 1608 |
|
| 1609 | lockdep_assert_held(&lock->wait_lock);
|
| 1610 |
|
| 1611 |
|
| 1612 | if (try_to_take_rt_mutex(lock, current, NULL)) {
|
| 1613 | if (build_ww_mutex() && ww_ctx) {
|
| 1614 | __ww_mutex_check_waiters(rtm, ww_ctx);
|
| 1615 | ww_mutex_lock_acquired(ww, ww_ctx);
|
| 1616 | }
|
| 1617 | return 0;
|
| 1618 | }
|
| 1619 |
|
| 1620 | set_current_state(state);
|
| 1621 |
|
| 1622 | trace_contention_begin(lock, LCB_F_RT);
|
| 1623 |
|
| 1624 | ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
|
| 1625 | if (likely(!ret))
|
| 1626 | ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);
|
| 1627 |
|
| 1628 | if (likely(!ret)) {
|
| 1629 |
|
| 1630 | if (build_ww_mutex() && ww_ctx) {
|
| 1631 | if (!ww_ctx->is_wait_die)
|
| 1632 | __ww_mutex_check_waiters(rtm, ww_ctx);
|
| 1633 | ww_mutex_lock_acquired(ww, ww_ctx);
|
| 1634 | }
|
| 1635 | } else {
|
| 1636 | __set_current_state(TASK_RUNNING);
|
| 1637 | remove_waiter(lock, waiter);
|
| 1638 | rt_mutex_handle_deadlock(ret, chwalk, waiter);
|
| 1639 | }
|
| 1640 |
|
| 1641 | |
| 1642 | * try_to_take_rt_mutex() sets the waiter bit
|
| 1643 | * unconditionally. We might have to fix that up.
|
| 1644 |
|
| 1645 | fixup_rt_mutex_waiters(lock, true);
|
| 1646 |
|
| 1647 | trace_contention_end(lock, ret);
|
| 1648 |
|
| 1649 | return ret;
|
| 1650 | }
|
| 1651 |
|
| 1652 | static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
|
| 1653 | struct ww_acquire_ctx *ww_ctx,
|
| 1654 | unsigned int state)
|
| 1655 | {
|
| 1656 | struct rt_mutex_waiter waiter;
|
| 1657 | int ret;
|
| 1658 |
|
| 1659 | rt_mutex_init_waiter(&waiter);
|
| 1660 | waiter.ww_ctx = ww_ctx;
|
| 1661 |
|
| 1662 | ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
|
| 1663 | &waiter);
|
| 1664 |
|
| 1665 | debug_rt_mutex_free_waiter(&waiter);
|
| 1666 | return ret;
|
| 1667 | }
|
| 1668 |
|
| 1669 | |
| 1670 | * rt_mutex_slowlock - Locking slowpath invoked when fast path fails
|
| 1671 | * @lock: The rtmutex to block lock
|
| 1672 | * @ww_ctx: WW mutex context pointer
|
| 1673 | * @state: The task state for sleeping
|
| 1674 |
|
| 1675 | static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
|
| 1676 | struct ww_acquire_ctx *ww_ctx,
|
| 1677 | unsigned int state)
|
| 1678 | {
|
| 1679 | unsigned long flags;
|
| 1680 | int ret;
|
| 1681 |
|
| 1682 | |
| 1683 | * Technically we could use raw_spin_[un]lock_irq() here, but this can
|
| 1684 | * be called in early boot if the cmpxchg() fast path is disabled
|
| 1685 | * (debug, no architecture support). In this case we will acquire the
|
| 1686 | * rtmutex with lock->wait_lock held. But we cannot unconditionally
|
| 1687 | * enable interrupts in that early boot case. So we need to use the
|
| 1688 | * irqsave/restore variants.
|
| 1689 |
|
| 1690 | raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
| 1691 | ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
|
| 1692 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
| 1693 |
|
| 1694 | return ret;
|
| 1695 | }
|
| 1696 |
|
| 1697 | static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
|
| 1698 | unsigned int state)
|
| 1699 | {
|
| 1700 | if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
|
| 1701 | return 0;
|
| 1702 |
|
| 1703 | return rt_mutex_slowlock(lock, NULL, state);
|
| 1704 | }
|
| 1705 | #endif
|
| 1706 |
|
| 1707 | #ifdef RT_MUTEX_BUILD_SPINLOCKS
|
| 1708 | |
| 1709 | * Functions required for spin/rw_lock substitution on RT kernels
|
| 1710 |
|
| 1711 |
|
| 1712 | |
| 1713 | * rtlock_slowlock_locked - Slow path lock acquisition for RT locks
|
| 1714 | * @lock: The underlying RT mutex
|
| 1715 |
|
| 1716 | static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
|
| 1717 | {
|
| 1718 | struct rt_mutex_waiter waiter;
|
| 1719 | struct task_struct *owner;
|
| 1720 |
|
| 1721 | lockdep_assert_held(&lock->wait_lock);
|
| 1722 |
|
| 1723 | if (try_to_take_rt_mutex(lock, current, NULL))
|
| 1724 | return;
|
| 1725 |
|
| 1726 | rt_mutex_init_rtlock_waiter(&waiter);
|
| 1727 |
|
| 1728 |
|
| 1729 | current_save_and_set_rtlock_wait_state();
|
| 1730 |
|
| 1731 | trace_contention_begin(lock, LCB_F_RT);
|
| 1732 |
|
| 1733 | task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK);
|
| 1734 |
|
| 1735 | for (;;) {
|
| 1736 |
|
| 1737 | if (try_to_take_rt_mutex(lock, current, &waiter))
|
| 1738 | break;
|
| 1739 |
|
| 1740 | if (&waiter == rt_mutex_top_waiter(lock))
|
| 1741 | owner = rt_mutex_owner(lock);
|
| 1742 | else
|
| 1743 | owner = NULL;
|
| 1744 | raw_spin_unlock_irq(&lock->wait_lock);
|
| 1745 |
|
| 1746 | if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner))
|
| 1747 | schedule_rtlock();
|
| 1748 |
|
| 1749 | raw_spin_lock_irq(&lock->wait_lock);
|
| 1750 | set_current_state(TASK_RTLOCK_WAIT);
|
| 1751 | }
|
| 1752 |
|
| 1753 |
|
| 1754 | current_restore_rtlock_saved_state();
|
| 1755 |
|
| 1756 | |
| 1757 | * try_to_take_rt_mutex() sets the waiter bit unconditionally.
|
| 1758 | * We might have to fix that up:
|
| 1759 |
|
| 1760 | fixup_rt_mutex_waiters(lock, true);
|
| 1761 | debug_rt_mutex_free_waiter(&waiter);
|
| 1762 |
|
| 1763 | trace_contention_end(lock, 0);
|
| 1764 | }
|
| 1765 |
|
| 1766 | static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
|
| 1767 | {
|
| 1768 | unsigned long flags;
|
| 1769 |
|
| 1770 | raw_spin_lock_irqsave(&lock->wait_lock, flags);
|
| 1771 | rtlock_slowlock_locked(lock);
|
| 1772 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
|
| 1773 | }
|
| 1774 |
|
| 1775 | #endif
|