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

------------------

From: Peter Zijlstra <pet...@infradead.org>

commit 8ef9b8455a2a3049efa9e46e8a6402b972a3eb41 upstream.

Alexander hit the WARN_ON_ONCE(!event) on his Skylake while running
the perf fuzzer.

This means the PEBSv3 record included a status bit for an inactive
event, something that _should_ not happen.

Move the code that filters the status bits against our known PEBS
events up a spot to guarantee we only deal with events we know about.

Further add "continue" statements to the WARN_ON_ONCE()s such that
we'll not die nor generate silly events in case we ever do hit them
again.

Reported-by: Alexander Shishkin <alexander.shish...@linux.intel.com>
Tested-by: Alexander Shishkin <alexander.shish...@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
Cc: Jiri Olsa <jo...@redhat.com>
Cc: Kan Liang <kan.li...@intel.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Stephane Eranian <eran...@google.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Vince Weaver <vi...@deater.net>
Fixes: a3d86542de88 ("perf/x86/intel/pebs: Add PEBSv3 decoding")
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 arch/x86/events/intel/ds.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1274,18 +1274,18 @@ static void intel_pmu_drain_pebs_nhm(str
                struct pebs_record_nhm *p = at;
                u64 pebs_status;
 
-               /* PEBS v3 has accurate status bits */
+               pebs_status = p->status & cpuc->pebs_enabled;
+               pebs_status &= (1ULL << x86_pmu.max_pebs_events) - 1;
+
+               /* PEBS v3 has more accurate status bits */
                if (x86_pmu.intel_cap.pebs_format >= 3) {
-                       for_each_set_bit(bit, (unsigned long *)&p->status,
-                                        MAX_PEBS_EVENTS)
+                       for_each_set_bit(bit, (unsigned long *)&pebs_status,
+                                        x86_pmu.max_pebs_events)
                                counts[bit]++;
 
                        continue;
                }
 
-               pebs_status = p->status & cpuc->pebs_enabled;
-               pebs_status &= (1ULL << x86_pmu.max_pebs_events) - 1;
-
                /*
                 * On some CPUs the PEBS status can be zero when PEBS is
                 * racing with clearing of GLOBAL_STATUS.
@@ -1333,8 +1333,11 @@ static void intel_pmu_drain_pebs_nhm(str
                        continue;
 
                event = cpuc->events[bit];
-               WARN_ON_ONCE(!event);
-               WARN_ON_ONCE(!event->attr.precise_ip);
+               if (WARN_ON_ONCE(!event))
+                       continue;
+
+               if (WARN_ON_ONCE(!event->attr.precise_ip))
+                       continue;
 
                /* log dropped samples number */
                if (error[bit])


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