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authorLinus Torvalds <torvalds@linux-foundation.org>2022-07-17 08:34:02 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-07-17 08:34:02 -0700
commit2b18593e4b9f5781a7683fca256036515bd9b946 (patch)
tree8d43f623e20a248cef69995cf5c62b58fead671c
parent59c80f053d50467758c8284348b463fa820b1b1f (diff)
parent68e3c69803dada336893640110cb87221bb01dcf (diff)
Merge tag 'perf_urgent_for_v5.19_rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull perf fix from Borislav Petkov: - A single data race fix on the perf event cleanup path to avoid endless loops due to insufficient locking * tag 'perf_urgent_for_v5.19_rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: perf/core: Fix data race between perf_event_set_output() and perf_mmap_close()
-rw-r--r--kernel/events/core.c45
1 files changed, 31 insertions, 14 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 80782cddb1da..d2b354991bf5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6253,10 +6253,10 @@ again:
if (!atomic_inc_not_zero(&event->rb->mmap_count)) {
/*
- * Raced against perf_mmap_close() through
- * perf_event_set_output(). Try again, hope for better
- * luck.
+ * Raced against perf_mmap_close(); remove the
+ * event and try again.
*/
+ ring_buffer_attach(event, NULL);
mutex_unlock(&event->mmap_mutex);
goto again;
}
@@ -11825,14 +11825,25 @@ err_size:
goto out;
}
+static void mutex_lock_double(struct mutex *a, struct mutex *b)
+{
+ if (b < a)
+ swap(a, b);
+
+ mutex_lock(a);
+ mutex_lock_nested(b, SINGLE_DEPTH_NESTING);
+}
+
static int
perf_event_set_output(struct perf_event *event, struct perf_event *output_event)
{
struct perf_buffer *rb = NULL;
int ret = -EINVAL;
- if (!output_event)
+ if (!output_event) {
+ mutex_lock(&event->mmap_mutex);
goto set;
+ }
/* don't allow circular references */
if (event == output_event)
@@ -11870,8 +11881,15 @@ perf_event_set_output(struct perf_event *event, struct perf_event *output_event)
event->pmu != output_event->pmu)
goto out;
+ /*
+ * Hold both mmap_mutex to serialize against perf_mmap_close(). Since
+ * output_event is already on rb->event_list, and the list iteration
+ * restarts after every removal, it is guaranteed this new event is
+ * observed *OR* if output_event is already removed, it's guaranteed we
+ * observe !rb->mmap_count.
+ */
+ mutex_lock_double(&event->mmap_mutex, &output_event->mmap_mutex);
set:
- mutex_lock(&event->mmap_mutex);
/* Can't redirect output if we've got an active mmap() */
if (atomic_read(&event->mmap_count))
goto unlock;
@@ -11881,6 +11899,12 @@ set:
rb = ring_buffer_get(output_event);
if (!rb)
goto unlock;
+
+ /* did we race against perf_mmap_close() */
+ if (!atomic_read(&rb->mmap_count)) {
+ ring_buffer_put(rb);
+ goto unlock;
+ }
}
ring_buffer_attach(event, rb);
@@ -11888,20 +11912,13 @@ set:
ret = 0;
unlock:
mutex_unlock(&event->mmap_mutex);
+ if (output_event)
+ mutex_unlock(&output_event->mmap_mutex);
out:
return ret;
}
-static void mutex_lock_double(struct mutex *a, struct mutex *b)
-{
- if (b < a)
- swap(a, b);
-
- mutex_lock(a);
- mutex_lock_nested(b, SINGLE_DEPTH_NESTING);
-}
-
static int perf_event_set_clock(struct perf_event *event, clockid_t clk_id)
{
bool nmi_safe = false;