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perf: Don't disable preemption in perf_pending_task().

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perf_pending_task() is invoked in task context and disables preemption
because perf_swevent_get_recursion_context() used to access per-CPU
variables. The other reason is to create a RCU read section while
accessing the perf_event.

The recursion counter is no longer a per-CPU accounter so disabling
preemption is no longer required. The RCU section is needed and must be
created explicit.

Replace the preemption-disable section with a explicit RCU-read section.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/r/20240704170424.1466941-7-bigeasy@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2024-07-04 19:03:40 +02:00 committed by Peter Zijlstra
parent 0d40a6d83e
commit 16b9569df9
1 changed files with 5 additions and 6 deletions
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11
kernel/events/core.c
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@ -5208,10 +5208,9 @@ static void perf_pending_task_sync(struct perf_event *event)
}
/*
* All accesses related to the event are within the same
* non-preemptible section in perf_pending_task(). The RCU
* grace period before the event is freed will make sure all
* those accesses are complete by then.
* All accesses related to the event are within the same RCU section in
* perf_pending_task(). The RCU grace period before the event is freed
* will make sure all those accesses are complete by then.
*/
rcuwait_wait_event(&event->pending_work_wait, !event->pending_work, TASK_UNINTERRUPTIBLE);
}
@ -6831,7 +6830,7 @@ static void perf_pending_task(struct callback_head *head)
* critical section as the ->pending_work reset. See comment in
* perf_pending_task_sync().
*/
preempt_disable_notrace();
rcu_read_lock();
/*
* If we 'fail' here, that's OK, it means recursion is already disabled
* and we won't recurse 'further'.
@ -6844,10 +6843,10 @@ static void perf_pending_task(struct callback_head *head)
local_dec(&event->ctx->nr_pending);
rcuwait_wake_up(&event->pending_work_wait);
}
rcu_read_unlock();
if (rctx >= 0)
perf_swevent_put_recursion_context(rctx);
preempt_enable_notrace();
}
#ifdef CONFIG_GUEST_PERF_EVENTS