| 1 | #include <linux/context_tracking.h>
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| 2 | #include <linux/rcupdate.h>
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| 3 | #include <linux/sched.h>
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| 4 | #include <linux/percpu.h>
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| 5 | #include <linux/hardirq.h>
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| 6 |
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| 7 | struct context_tracking {
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| 8 | |
| 9 | * When active is false, hooks are not set to
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| 10 | * minimize overhead: TIF flags are cleared
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| 11 | * and calls to user_enter/exit are ignored. This
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| 12 | * may be further optimized using static keys.
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| 13 |
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| 14 | bool active;
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| 15 | enum {
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| 16 | IN_KERNEL = 0,
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| 17 | IN_USER,
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| 18 | } state;
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| 19 | };
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| 20 |
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| 21 | static DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
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| 22 | #ifdef CONFIG_CONTEXT_TRACKING_FORCE
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| 23 | .active = true,
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| 24 | #endif
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| 25 | };
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| 26 |
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| 27 | void user_enter(void)
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| 28 | {
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| 29 | unsigned long flags;
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| 30 |
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| 31 | |
| 32 | * Some contexts may involve an exception occuring in an irq,
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| 33 | * leading to that nesting:
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| 34 | * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
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| 35 | * This would mess up the dyntick_nesting count though. And rcu_irq_*()
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| 36 | * helpers are enough to protect RCU uses inside the exception. So
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| 37 | * just return immediately if we detect we are in an IRQ.
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| 38 |
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| 39 | if (in_interrupt())
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| 40 | return;
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| 41 |
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| 42 | WARN_ON_ONCE(!current->mm);
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| 43 |
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| 44 | local_irq_save(flags);
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| 45 | if (__this_cpu_read(context_tracking.active) &&
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| 46 | __this_cpu_read(context_tracking.state) != IN_USER) {
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| 47 | __this_cpu_write(context_tracking.state, IN_USER);
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| 48 | rcu_user_enter();
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| 49 | }
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| 50 | local_irq_restore(flags);
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| 51 | }
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| 52 |
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| 53 | void user_exit(void)
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| 54 | {
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| 55 | unsigned long flags;
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| 56 |
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| 57 | |
| 58 | * Some contexts may involve an exception occuring in an irq,
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| 59 | * leading to that nesting:
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| 60 | * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
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| 61 | * This would mess up the dyntick_nesting count though. And rcu_irq_*()
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| 62 | * helpers are enough to protect RCU uses inside the exception. So
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| 63 | * just return immediately if we detect we are in an IRQ.
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| 64 |
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| 65 | if (in_interrupt())
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| 66 | return;
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| 67 |
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| 68 | local_irq_save(flags);
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| 69 | if (__this_cpu_read(context_tracking.state) == IN_USER) {
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| 70 | __this_cpu_write(context_tracking.state, IN_KERNEL);
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| 71 | rcu_user_exit();
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| 72 | }
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| 73 | local_irq_restore(flags);
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| 74 | }
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| 75 |
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| 76 | void context_tracking_task_switch(struct task_struct *prev,
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| 77 | struct task_struct *next)
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| 78 | {
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| 79 | if (__this_cpu_read(context_tracking.active)) {
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| 80 | clear_tsk_thread_flag(prev, TIF_NOHZ);
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| 81 | set_tsk_thread_flag(next, TIF_NOHZ);
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| 82 | }
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| 83 | }
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