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perf: Simplify perf_event_free_task() wait

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Simplify the code by moving the duplicated wakeup condition into
put_ctx().

Notably, wait_var_event() is in perf_event_free_task() and will have
set ctx->task = TASK_TOMBSTONE.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lkml.kernel.org/r/20250307193723.044499344@infradead.org
This commit is contained in:
Peter Zijlstra 2025-01-17 15:27:07 +01:00
parent 0a00a43b8c
commit 59f3aa4a3e
1 changed files with 3 additions and 22 deletions
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25
kernel/events/core.c
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@ -1270,6 +1270,9 @@ static void put_ctx(struct perf_event_context *ctx)
if (ctx->task && ctx->task != TASK_TOMBSTONE)
put_task_struct(ctx->task);
call_rcu(&ctx->rcu_head, free_ctx);
} else if (ctx->task == TASK_TOMBSTONE) {
smp_mb(); /* pairs with wait_var_event() */
wake_up_var(&ctx->refcount);
}
}
@ -5729,8 +5732,6 @@ int perf_event_release_kernel(struct perf_event *event)
again:
mutex_lock(&event->child_mutex);
list_for_each_entry(child, &event->child_list, child_list) {
void *var = NULL;
/*
* Cannot change, child events are not migrated, see the
* comment with perf_event_ctx_lock_nested().
@ -5765,40 +5766,20 @@ int perf_event_release_kernel(struct perf_event *event)
if (tmp == child) {
perf_remove_from_context(child, DETACH_GROUP | DETACH_CHILD);
list_add(&child->child_list, &free_list);
} else {
var = &ctx->refcount;
}
mutex_unlock(&event->child_mutex);
mutex_unlock(&ctx->mutex);
put_ctx(ctx);
if (var) {
/*
* If perf_event_free_task() has deleted all events from the
* ctx while the child_mutex got released above, make sure to
* notify about the preceding put_ctx().
*/
smp_mb(); /* pairs with wait_var_event() */
wake_up_var(var);
}
goto again;
}
mutex_unlock(&event->child_mutex);
list_for_each_entry_safe(child, tmp, &free_list, child_list) {
void *var = &child->ctx->refcount;
list_del(&child->child_list);
/* Last reference unless ->pending_task work is pending */
put_event(child);
/*
* Wake any perf_event_free_task() waiting for this event to be
* freed.
*/
smp_mb(); /* pairs with wait_var_event() */
wake_up_var(var);
}
no_ctx: