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Message-ID: <172052531756.2215.11237686920365836246.tip-bot2@tip-bot2>
Date: Tue, 09 Jul 2024 11:41:57 -0000
From: "tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Marco Elver <elver@...gle.com>, x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
[tip: perf/core] perf: Don't disable preemption in perf_pending_task().
The following commit has been merged into the perf/core branch of tip:
Commit-ID: 16b9569df9d2ab07eeee075cb7895e9d3e08e8f0
Gitweb: https://git.kernel.org/tip/16b9569df9d2ab07eeee075cb7895e9d3e08e8f0
Author: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate: Thu, 04 Jul 2024 19:03:40 +02:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 09 Jul 2024 13:26:36 +02:00
perf: Don't disable preemption in perf_pending_task().
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@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Marco Elver <elver@...gle.com>
Link: https://lore.kernel.org/r/20240704170424.1466941-7-bigeasy@linutronix.de
---
kernel/events/core.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index b523225..96e03d6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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
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