[PATCH] perf: Fix AUX output stopping

[PATCH] perf: Fix AUX output stopping

[Alexander Shishkin]

Commit

  8a58ddae2379 ("perf/core: Fix exclusive events' grouping")

allows CAP_EXCLUSIVE events to be grouped with other events. Since all
of those also happen to be AUX events (which is not the case the other
way around, because arch/s390), this changes the rules for stopping the
output: the AUX event may not be on its PMU's context any more, if it's
grouped with a HW event, in which case it will be on that HW event's
context instead. If that's the case, munmap() of the AUX buffer can't
find and stop the AUX event, potentially leaving the last reference with
the atomic context, which will then end up freeing the AUX buffer. This
will then trip warnings:

> WARNING: CPU: 2 PID: 318 at kernel/events/core.c:5615 perf_mmap_close+0x839/0x850
> Modules linked in:
> CPU: 2 PID: 318 Comm: exclusive-group Tainted: G W 5.4.0-rc3-00070-g39b656ee9f2c #846
> RIP: 0010:perf_mmap_close+0x839/0x850

Fix this by using the context's PMU context when looking for events
to stop, instead of the event's PMU context.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: stable@vger.kernel.org
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5bbaabdad068..77793ef0d8bc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6965,7 +6965,7 @@ static void __perf_event_output_stop(struct perf_event *event, void *data)
 static int __perf_pmu_output_stop(void *info)
 {
 	struct perf_event *event = info;
-	struct pmu *pmu = event->pmu;
+	struct pmu *pmu = event->ctx->pmu;
 	struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
 	struct remote_output ro = {
 		.rb	= event->rb,
-- 
2.23.0

[tip: perf/urgent] perf/aux: Fix AUX output stopping

[tip-bot2 for Alexander Shishkin]

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     f3a519e4add93b7b31a6616f0b09635ff2e6a159
Gitweb:        https://git.kernel.org/tip/f3a519e4add93b7b31a6616f0b09635ff2e6a159
Author:        Alexander Shishkin <alexander.shishkin@linux.intel.com>
AuthorDate:    Tue, 22 Oct 2019 10:39:40 +03:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 22 Oct 2019 14:39:37 +02:00

perf/aux: Fix AUX output stopping

Commit:

  8a58ddae2379 ("perf/core: Fix exclusive events' grouping")

allows CAP_EXCLUSIVE events to be grouped with other events. Since all
of those also happen to be AUX events (which is not the case the other
way around, because arch/s390), this changes the rules for stopping the
output: the AUX event may not be on its PMU's context any more, if it's
grouped with a HW event, in which case it will be on that HW event's
context instead. If that's the case, munmap() of the AUX buffer can't
find and stop the AUX event, potentially leaving the last reference with
the atomic context, which will then end up freeing the AUX buffer. This
will then trip warnings:

Fix this by using the context's PMU context when looking for events
to stop, instead of the event's PMU context.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20191022073940.61814-1-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index f5d7950..bb3748d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6949,7 +6949,7 @@ static void __perf_event_output_stop(struct perf_event *event, void *data)
 static int __perf_pmu_output_stop(void *info)
 {
 	struct perf_event *event = info;
-	struct pmu *pmu = event->pmu;
+	struct pmu *pmu = event->ctx->pmu;
 	struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
 	struct remote_output ro = {
 		.rb	= event->rb,