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perf/x86/intel/pt: Fix sampling synchronization

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pt_event_snapshot_aux() uses pt->handle_nmi to determine if tracing
needs to be stopped, however tracing can still be going because
pt->handle_nmi is set to zero before tracing is stopped in pt_event_stop,
whereas pt_event_snapshot_aux() requires that tracing must be stopped in
order to copy a sample of trace from the buffer.

Instead call pt_config_stop() always, which anyway checks config for
RTIT_CTL_TRACEEN and does nothing if it is already clear.

Note pt_event_snapshot_aux() can continue to use pt->handle_nmi to
determine if the trace needs to be restarted afterwards.

Fixes: 25e8920b30 ("perf/x86/intel/pt: Add sampling support")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20240715160712.127117-2-adrian.hunter@intel.com
This commit is contained in:
Adrian Hunter 2024-07-15 19:07:00 +03:00 committed by Peter Zijlstra
parent b1d0e15c87
commit d92792a4b2
1 changed files with 7 additions and 8 deletions
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15
arch/x86/events/intel/pt.c
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@ -1606,6 +1606,7 @@ static void pt_event_stop(struct perf_event *event, int mode)
* see comment in intel_pt_interrupt().
*/
WRITE_ONCE(pt->handle_nmi, 0);
barrier();
pt_config_stop(event);
@ -1657,11 +1658,10 @@ static long pt_event_snapshot_aux(struct perf_event *event,
return 0;
/*
* Here, handle_nmi tells us if the tracing is on
* There is no PT interrupt in this mode, so stop the trace and it will
* remain stopped while the buffer is copied.
*/
if (READ_ONCE(pt->handle_nmi))
pt_config_stop(event);
pt_config_stop(event);
pt_read_offset(buf);
pt_update_head(pt);
@ -1673,11 +1673,10 @@ static long pt_event_snapshot_aux(struct perf_event *event,
ret = perf_output_copy_aux(&pt->handle, handle, from, to);
/*
* If the tracing was on when we turned up, restart it.
* Compiler barrier not needed as we couldn't have been
* preempted by anything that touches pt->handle_nmi.
* Here, handle_nmi tells us if the tracing was on.
* If the tracing was on, restart it.
*/
if (pt->handle_nmi)
if (READ_ONCE(pt->handle_nmi))
pt_config_start(event);
return ret;