Commit 92ca7da4 authored Dec 10, 2019 by Alexander Shishkin Committed by Peter Zijlstra Dec 17, 2019

perf/x86/intel: Fix PT PMI handling

Commit:

ccbebba4 ("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: ccbebba4 ("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

parent ff61541c

arch/x86/events/core.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -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)