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Message-ID: <20240322065208.60456-4-bigeasy@linutronix.de>
Date: Fri, 22 Mar 2024 07:48:23 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: Adrian Hunter <adrian.hunter@...el.com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Ingo Molnar <mingo@...hat.com>,
Jiri Olsa <jolsa@...nel.org>,
Marco Elver <elver@...gle.com>,
Mark Rutland <mark.rutland@....com>,
Namhyung Kim <namhyung@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH v3 3/4] perf: Remove perf_swevent_get_recursion_context() from perf_pending_task().
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@...gle.com>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
kernel/events/core.c | 12 ------------
1 file changed, 12 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index e0b2da8de485f..5400f7ed2f98b 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
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