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@xxxxxxxxxxxxx> AuthorDate: Thu, 04 Jul 2024 19:03:40 +02:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Tested-by: Marco Elver <elver@xxxxxxxxxx> Link: https://lore.kernel.org/r/20240704170424.1466941-7-bigeasy@xxxxxxxxxxxxx --- 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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