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perf/x86/intel: Fix PT PMI handling

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Commit:

  ccbebba4c6 ("perf/x86/intel/pt: Bypass PT vs. LBR exclusivity if the core supports it")

skips the PT/LBR exclusivity check on CPUs where PT and LBRs coexist, but
also inadvertently skips the active_events bump for PT in that case, which
is a bug. If there aren't any hardware events at the same time as PT, the
PMI handler will ignore PT PMIs, as active_events reads zero in that case,
resulting in the "Uhhuh" spurious NMI warning and PT data loss.

Fix this by always increasing active_events for PT events.

Fixes: ccbebba4c6 ("perf/x86/intel/pt: Bypass PT vs. LBR exclusivity if the core supports it")
Reported-by: Vitaly Slobodskoy <vitaly.slobodskoy@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lkml.kernel.org/r/20191210105101.77210-1-alexander.shishkin@linux.intel.com
This commit is contained in:
Alexander Shishkin 2019-12-10 12:51:01 +02:00 committed by Peter Zijlstra
parent ff61541cc6
commit 92ca7da4bd
1 changed files with 7 additions and 2 deletions
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9
arch/x86/events/core.c
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@ -376,7 +376,7 @@ int x86_add_exclusive(unsigned int what)
* LBR and BTS are still mutually exclusive.
*/
if (x86_pmu.lbr_pt_coexist && what == x86_lbr_exclusive_pt)
return 0;
goto out;
if (!atomic_inc_not_zero(&x86_pmu.lbr_exclusive[what])) {
mutex_lock(&pmc_reserve_mutex);
@ -388,6 +388,7 @@ int x86_add_exclusive(unsigned int what)
mutex_unlock(&pmc_reserve_mutex);
}
out:
atomic_inc(&active_events);
return 0;
@ -398,11 +399,15 @@ fail_unlock:
void x86_del_exclusive(unsigned int what)
{
atomic_dec(&active_events);
/*
* See the comment in x86_add_exclusive().
*/
if (x86_pmu.lbr_pt_coexist && what == x86_lbr_exclusive_pt)
return;
atomic_dec(&x86_pmu.lbr_exclusive[what]);
atomic_dec(&active_events);
}
int x86_setup_perfctr(struct perf_event *event)