From: Sebastian Andrzej Siewior 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 Tested-by: Arnaldo Carvalho de Melo Reported-by: Arnaldo Carvalho de Melo Link: https://lore.kernel.org/r/20240312180814.3373778-4-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior --- 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); }