[PATCH 4.2.y-ckt 22/53] perf/core: Disable the event on a truncated AUX record

From: Kamal Mostafa
Date: Tue May 24 2016 - 13:57:51 EST

4.2.8-ckt11 -stable review patch. If anyone has any objections, please let me know.


From: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>

commit 9f448cd3cbcec8995935e60b27802ae56aac8cc0 upstream.

When the PMU driver reports a truncated AUX record, it effectively means
that there is no more usable room in the event's AUX buffer (even though
there may still be some room, so that perf_aux_output_begin() doesn't take
action). At this point the consumer still has to be woken up and the event
has to be disabled, otherwise the event will just keep spinning between
perf_aux_output_begin() and perf_aux_output_end() until its context gets

Again, for cpu-wide events this means never, so once in this condition,
they will be forever losing data.

Fix this by disabling the event and waking up the consumer in case of a
truncated AUX record.

Reported-by: Markus Metzger <markus.t.metzger@xxxxxxxxx>
Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: vince@xxxxxxxxxx
Link: http://lkml.kernel.org/r/1462886313-13660-3-git-send-email-alexander.shishkin@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
kernel/events/ring_buffer.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index c8aa3f7..6676592 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -347,6 +347,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
bool truncated)
struct ring_buffer *rb = handle->rb;
+ bool wakeup = truncated;
unsigned long aux_head;
u64 flags = 0;

@@ -375,9 +376,16 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);

if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
- perf_output_wakeup(handle);
+ wakeup = true;
local_add(rb->aux_watermark, &rb->aux_wakeup);
+ if (wakeup) {
+ if (truncated)
+ handle->event->pending_disable = 1;
+ perf_output_wakeup(handle);
+ }
handle->event = NULL;

local_set(&rb->aux_nest, 0);