[PATCH v2 3/4] perf: Remove perf_swevent_get_recursion_context() from perf_pending_task().

Sebastian Andrzej Siewior
2024-03-12T18:08:21Z

perf_swevent_get_recursion_context() is supposed to avoid recursion.
This requires to remain on the same CPU in order to decrement/ increment
the same counter. This is done by using preempt_disable(). Having
preemption disabled while sending a signal leads to locking problems on
PREEMPT_RT because sighand, a spinlock_t, becomes a sleeping lock.

This callback runs in task context and currently delivers only a signal
to "itself". Any kind of recusrion protection in this context is not
required.

Remove recursion protection in perf_pending_task().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/events/core.c | 12 ------------
1 file changed, 12 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index e9926baaa1587..806514d76d8dc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6785,14 +6785,6 @@ static void perf_pending_irq(struct irq_work *entry)
static void perf_pending_task(struct callback_head *head)
{
struct perf_event *event = container_of(head, struct perf_event, pending_task);
- int rctx;
-
- /*
- * If we 'fail' here, that's OK, it means recursion is already disabled
- * and we won't recurse 'further'.
- */
- preempt_disable_notrace();
- rctx = perf_swevent_get_recursion_context();

if (event->pending_work) {
event->pending_work = 0;
@@ -6800,10 +6792,6 @@ static void perf_pending_task(struct callback_head *head)
local_dec(&event->ctx->nr_pending);
}

- if (rctx >= 0)
- perf_swevent_put_recursion_context(rctx);
- preempt_enable_notrace();
-
put_event(event);
}

--
2.43.0