diff --git a/kernel/events/core.c b/kernel/events/core.c
index 06ae52e..5946460 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -49,8 +49,6 @@
#include <asm/irq_regs.h>
-static struct workqueue_struct *perf_wq;
-
typedef int (*remote_function_f)(void *);
struct remote_function_call {
@@ -126,44 +124,181 @@ static int cpu_function_call(int cpu, remote_function_f func, void *info)
return data.ret;
}
-static void event_function_call(struct perf_event *event,
- int (*active)(void *),
- void (*inactive)(void *),
- void *data)
+static inline struct perf_cpu_context *
+__get_cpu_context(struct perf_event_context *ctx)
+{
+ return this_cpu_ptr(ctx->pmu->pmu_cpu_context);
+}
+
+static void perf_ctx_lock(struct perf_cpu_context *cpuctx,
+ struct perf_event_context *ctx)
{
+ raw_spin_lock(&cpuctx->ctx.lock);
+ if (ctx)
+ raw_spin_lock(&ctx->lock);
+}
+
+static void perf_ctx_unlock(struct perf_cpu_context *cpuctx,
+ struct perf_event_context *ctx)
+{
+ if (ctx)
+ raw_spin_unlock(&ctx->lock);
+ raw_spin_unlock(&cpuctx->ctx.lock);
+}
+
+#define TASK_TOMBSTONE ((void *)-1L)
+
+static bool is_kernel_event(struct perf_event *event)
+{
+ return READ_ONCE(event->owner) == TASK_TOMBSTONE;
+}
+
+/*
+ * On task ctx scheduling...
+ *
+ * When !ctx->nr_events a task context will not be scheduled. This means
+ * we can disable the scheduler hooks (for performance) without leaving
+ * pending task ctx state.
+ *
+ * This however results in two special cases:
+ *
+ * - removing the last event from a task ctx; this is relatively straight
+ * forward and is done in __perf_remove_from_context.
+ *
+ * - adding the first event to a task ctx; this is tricky because we cannot
+ * rely on ctx->is_active and therefore cannot use event_function_call().
+ * See perf_install_in_context().
+ *
+ * This is because we need a ctx->lock serialized variable (ctx->is_active)
+ * to reliably determine if a particular task/context is scheduled in. The
+ * task_curr() use in task_function_call() is racy in that a remote context
+ * switch is not a single atomic operation.
+ *
+ * As is, the situation is 'safe' because we set rq->curr before we do the
+ * actual context switch. This means that task_curr() will fail early, but
+ * we'll continue spinning on ctx->is_active until we've passed
+ * perf_event_task_sched_out().
+ *
+ * Without this ctx->lock serialized variable we could have race where we find
+ * the task (and hence the context) would not be active while in fact they are.
+ *
+ * If ctx->nr_events, then ctx->is_active and cpuctx->task_ctx are set.
+ */
+
+typedef void (*event_f)(struct perf_event *, struct perf_cpu_context *,
+ struct perf_event_context *, void *);
+
+struct event_function_struct {
+ struct perf_event *event;
+ event_f func;
+ void *data;
+};
+
+static int event_function(void *info)
+{
+ struct event_function_struct *efs = info;
+ struct perf_event *event = efs->event;
struct perf_event_context *ctx = event->ctx;
- struct task_struct *task = ctx->task;
+ struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
+ struct perf_event_context *task_ctx = cpuctx->task_ctx;
+ int ret = 0;
+
+ WARN_ON_ONCE(!irqs_disabled());
+
+ perf_ctx_lock(cpuctx, task_ctx);
+ /*
+ * Since we do the IPI call without holding ctx->lock things can have
+ * changed, double check we hit the task we set out to hit.
+ */
+ if (ctx->task) {
+ if (ctx->task != current) {
+ ret = -EAGAIN;
+ goto unlock;
+ }
+
+ /*
+ * We only use event_function_call() on established contexts,
+ * and event_function() is only ever called when active (or
+ * rather, we'll have bailed in task_function_call() or the
+ * above ctx->task != current test), therefore we must have
+ * ctx->is_active here.
+ */
+ WARN_ON_ONCE(!ctx->is_active);
+ /*
+ * And since we have ctx->is_active, cpuctx->task_ctx must
+ * match.
+ */
+ WARN_ON_ONCE(task_ctx != ctx);
+ } else {
+ WARN_ON_ONCE(&cpuctx->ctx != ctx);
+ }
+
+ efs->func(event, cpuctx, ctx, efs->data);
+unlock:
+ perf_ctx_unlock(cpuctx, task_ctx);
+
+ return ret;
+}
+
+static void event_function_local(struct perf_event *event, event_f func, void *data)
+{
+ struct event_function_struct efs = {
+ .event = event,
+ .func = func,
+ .data = data,
+ };
+
+ int ret = event_function(&efs);
+ WARN_ON_ONCE(ret);
+}
+
+static void event_function_call(struct perf_event *event, event_f func, void *data)
+{
+ struct perf_event_context *ctx = event->ctx;
+ struct task_struct *task = READ_ONCE(ctx->task); /* verified in event_function */
+ struct event_function_struct efs = {
+ .event = event,
+ .func = func,
+ .data = data,
+ };
+
+ if (!event->parent) {
+ /*
+ * If this is a !child event, we must hold ctx::mutex to
+ * stabilize the the event->ctx relation. See
+ * perf_event_ctx_lock().
+ */
+ lockdep_assert_held(&ctx->mutex);
+ }
if (!task) {
- cpu_function_call(event->cpu, active, data);
+ cpu_function_call(event->cpu, event_function, &efs);
return;
}
again:
- if (!task_function_call(task, active, data))
+ if (task == TASK_TOMBSTONE)
+ return;
+
+ if (!task_function_call(task, event_function, &efs))
return;
raw_spin_lock_irq(&ctx->lock);
- if (ctx->is_active) {
- /*
- * Reload the task pointer, it might have been changed by
- * a concurrent perf_event_context_sched_out().
- */
- task = ctx->task;
- raw_spin_unlock_irq(&ctx->lock);
- goto again;
+ /*
+ * Reload the task pointer, it might have been changed by
+ * a concurrent perf_event_context_sched_out().
+ */
+ task = ctx->task;
+ if (task != TASK_TOMBSTONE) {
+ if (ctx->is_active) {
+ raw_spin_unlock_irq(&ctx->lock);
+ goto again;
+ }
+ func(event, NULL, ctx, data);
}
- inactive(data);
raw_spin_unlock_irq(&ctx->lock);
}
-#define EVENT_OWNER_KERNEL ((void *) -1)
-
-static bool is_kernel_event(struct perf_event *event)
-{
- return event->owner == EVENT_OWNER_KERNEL;
-}
-
#define PERF_FLAG_ALL (PERF_FLAG_FD_NO_GROUP |\
PERF_FLAG_FD_OUTPUT |\
PERF_FLAG_PID_CGROUP |\
@@ -368,28 +503,6 @@ static inline u64 perf_event_clock(struct perf_event *event)
return event->clock();
}
-static inline struct perf_cpu_context *
-__get_cpu_context(struct perf_event_context *ctx)
-{
- return this_cpu_ptr(ctx->pmu->pmu_cpu_context);
-}
-
-static void perf_ctx_lock(struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx)
-{
- raw_spin_lock(&cpuctx->ctx.lock);
- if (ctx)
- raw_spin_lock(&ctx->lock);
-}
-
-static void perf_ctx_unlock(struct perf_cpu_context *cpuctx,
- struct perf_event_context *ctx)
-{
- if (ctx)
- raw_spin_unlock(&ctx->lock);
- raw_spin_unlock(&cpuctx->ctx.lock);
-}
-
#ifdef CONFIG_CGROUP_PERF
static inline bool
@@ -579,13 +692,7 @@ static inline void perf_cgroup_sched_out(struct task_struct *task,
* we are holding the rcu lock
*/
cgrp1 = perf_cgroup_from_task(task, NULL);
-
- /*
- * next is NULL when called from perf_event_enable_on_exec()
- * that will systematically cause a cgroup_switch()
- */
- if (next)
- cgrp2 = perf_cgroup_from_task(next, NULL);
+ cgrp2 = perf_cgroup_from_task(next, NULL);
/*
* only schedule out current cgroup events if we know
@@ -611,8 +718,6 @@ static inline void perf_cgroup_sched_in(struct task_struct *prev,
* we are holding the rcu lock
*/
cgrp1 = perf_cgroup_from_task(task, NULL);
-
- /* prev can never be NULL */
cgrp2 = perf_cgroup_from_task(prev, NULL);
/*
@@ -917,7 +1022,7 @@ static void put_ctx(struct perf_event_context *ctx)
if (atomic_dec_and_test(&ctx->refcount)) {
if (ctx->parent_ctx)
put_ctx(ctx->parent_ctx);
- if (ctx->task)
+ if (ctx->task && ctx->task != TASK_TOMBSTONE)
put_task_struct(ctx->task);
call_rcu(&ctx->rcu_head, free_ctx);
}
@@ -934,9 +1039,8 @@ static void put_ctx(struct perf_event_context *ctx)
* perf_event_context::mutex nests and those are:
*
* - perf_event_exit_task_context() [ child , 0 ]
- * __perf_event_exit_task()
- * sync_child_event()
- * put_event() [ parent, 1 ]
+ * perf_event_exit_event()
+ * put_event() [ parent, 1 ]
*
* - perf_event_init_context() [ parent, 0 ]
* inherit_task_group()
@@ -979,8 +1083,8 @@ static void put_ctx(struct perf_event_context *ctx)
* Lock order:
* task_struct::perf_event_mutex
* perf_event_context::mutex
- * perf_event_context::lock
* perf_event::child_mutex;
+ * perf_event_context::lock
* perf_event::mmap_mutex
* mmap_sem
*/
@@ -1078,6 +1182,7 @@ static u64 primary_event_id(struct perf_event *event)
/*
* Get the perf_event_context for a task and lock it.
+ *
* This has to cope with with the fact that until it is locked,
* the context could get moved to another task.
*/
@@ -1118,9 +1223,12 @@ retry:
goto retry;
}
- if (!atomic_inc_not_zero(&ctx->refcount)) {
+ if (ctx->task == TASK_TOMBSTONE ||
+ !atomic_inc_not_zero(&ctx->refcount)) {
raw_spin_unlock(&ctx->lock);
ctx = NULL;
+ } else {
+ WARN_ON_ONCE(ctx->task != task);
}
}
rcu_read_unlock();
@@ -1246,6 +1354,8 @@ ctx_group_list(struct perf_event *event, struct perf_event_context *ctx)
static void
list_add_event(struct perf_event *event, struct perf_event_context *ctx)
{
+ lockdep_assert_held(&ctx->lock);
+
WARN_ON_ONCE(event->attach_state & PERF_ATTACH_CONTEXT);
event->attach_state |= PERF_ATTACH_CONTEXT;
@@ -1448,11 +1558,14 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
if (is_cgroup_event(event)) {
ctx->nr_cgroups--;
+ /*
+ * Because cgroup events are always per-cpu events, this will
+ * always be called from the right CPU.
+ */
cpuctx = __get_cpu_context(ctx);
/*
- * if there are no more cgroup events
- * then cler cgrp to avoid stale pointer
- * in update_cgrp_time_from_cpuctx()
+ * If there are no more cgroup events then clear cgrp to avoid
+ * stale pointer in update_cgrp_time_from_cpuctx().
*/
if (!ctx->nr_cgroups)
cpuctx->cgrp = NULL;
@@ -1530,45 +1643,11 @@ out:
perf_event__header_size(tmp);
}
-/*
- * User event without the task.
- */
static bool is_orphaned_event(struct perf_event *event)
{
- return event && !is_kernel_event(event) && !event->owner;
+ return event->state == PERF_EVENT_STATE_EXIT;
}
-/*
- * Event has a parent but parent's task finished and it's
- * alive only because of children holding refference.
- */
-static bool is_orphaned_child(struct perf_event *event)
-{
- return is_orphaned_event(event->parent);
-}
-
-static void orphans_remove_work(struct work_struct *work);
-
-static void schedule_orphans_remove(struct perf_event_context *ctx)
-{
- if (!ctx->task || ctx->orphans_remove_sched || !perf_wq)
- return;
-
- if (queue_delayed_work(perf_wq, &ctx->orphans_remove, 1)) {
- get_ctx(ctx);
- ctx->orphans_remove_sched = true;
- }
-}
-
-static int __init perf_workqueue_init(void)
-{
- perf_wq = create_singlethread_workqueue("perf");
- WARN(!perf_wq, "failed to create perf workqueue\n");
- return perf_wq ? 0 : -1;
-}
-