Eric Lee / linux-smarc-t335x-v3.2

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Commit 4ec8363dfc1451f8c8f86825731fe712798ada02

Authored by Vince Weaver
Committed by Ingo Molnar
1 parent 0f933625e7
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

perf_events: Fix perf buffer watermark setting 

Since 2.6.36 (specifically commit d57e34fdd60b ("perf: Simplify the
ring-buffer logic: make perf_buffer_alloc() do everything needed"),
the perf_buffer_init_code() has been mis-setting the buffer watermark
if perf_event_attr.wakeup_events has a non-zero value.

This is because perf_event_attr.wakeup_events is a union with
perf_event_attr.wakeup_watermark.

This commit re-enables the check for perf_event_attr.watermark being
set before continuing with setting a non-default watermark.

This bug is most noticable when you are trying to use PERF_IOC_REFRESH
with a value larger than one and perf_event_attr.wakeup_events is set to
one.  In this case the buffer watermark will be set to 1 and you will
get extraneous POLL_IN overflows rather than POLL_HUP as expected.

[ avoid using attr.wakeup_events when attr.watermark is set ]

Signed-off-by: Vince Weaver <vweaver1@eecs.utk.edu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1106011506390.5384@cl320.eecs.utk.edu
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Showing 2 changed files with 13 additions and 9 deletions Side-by-side Diff

kernel/events/core.c
Diff comments   View file @ 4ec8363
... ... @@ -3569,8 +3569,10 @@
3569 3569 if (vma->vm_flags & VM_WRITE)
3570 3570 flags |= RING_BUFFER_WRITABLE;
3571 3571  
3572   - rb = rb_alloc(nr_pages, event->attr.wakeup_watermark,
3573   - event->cpu, flags);
  3572 + rb = rb_alloc(nr_pages,
  3573 + event->attr.watermark ? event->attr.wakeup_watermark : 0,
  3574 + event->cpu, flags);
  3575 +
3574 3576 if (!rb) {
3575 3577 ret = -ENOMEM;
3576 3578 goto unlock;
kernel/events/ring_buffer.c
Diff comments   View file @ 4ec8363
... ... @@ -199,13 +199,15 @@
199 199 struct perf_event *event = handle->event;
200 200 struct ring_buffer *rb = handle->rb;
201 201  
202   - int wakeup_events = event->attr.wakeup_events;
  202 + if (handle->sample && !event->attr.watermark) {
  203 + int wakeup_events = event->attr.wakeup_events;
203 204  
204   - if (handle->sample && wakeup_events) {
205   - int events = local_inc_return(&rb->events);
206   - if (events >= wakeup_events) {
207   - local_sub(wakeup_events, &rb->events);
208   - local_inc(&rb->wakeup);
  205 + if (wakeup_events) {
  206 + int events = local_inc_return(&rb->events);
  207 + if (events >= wakeup_events) {
  208 + local_sub(wakeup_events, &rb->events);
  209 + local_inc(&rb->wakeup);
  210 + }
209 211 }
210 212 }
211 213