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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Tue, 12 Mar 2024 19:01:51 +0100
Subject: [PATCH 3/4] perf: Remove perf_swevent_get_recursion_context() from
perf_pending_task().
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.8/older/patches-6.8.2-rt11.tar.xz
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().
Tested-by: Marco Elver <elver@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/20240312180814.3373778-4-bigeasy@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/events/core.c | 12 ------------
1 file changed, 12 deletions(-)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6785,14 +6785,6 @@ static void perf_pending_irq(struct irq_
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 cal
local_dec(&event->ctx->nr_pending);
}
- if (rctx >= 0)
- perf_swevent_put_recursion_context(rctx);
- preempt_enable_notrace();
-
put_event(event);
}
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