Vince reported crash in bts flush code when touching the callchain
data, which was supposed to be initialized as an 'early' callchain,
but intel_pmu_drain_bts_buffer does not do that.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
...
Call Trace:
<IRQ>
intel_pmu_drain_bts_buffer+0x151/0x220
? intel_get_event_constraints+0x219/0x360
? perf_assign_events+0xe2/0x2a0
? select_idle_sibling+0x22/0x3a0
? __update_load_avg_se+0x1ec/0x270
? enqueue_task_fair+0x377/0xdd0
? cpumask_next_and+0x19/0x20
? load_balance+0x134/0x950
? check_preempt_curr+0x7a/0x90
? ttwu_do_wakeup+0x19/0x140
x86_pmu_stop+0x3b/0x90
x86_pmu_del+0x57/0x160
event_sched_out.isra.106+0x81/0x170
group_sched_out.part.108+0x51/0xc0
__perf_event_disable+0x7f/0x160
event_function+0x8c/0xd0
remote_function+0x3c/0x50
flush_smp_call_function_queue+0x35/0xe0
smp_call_function_single_interrupt+0x3a/0xd0
call_function_single_interrupt+0xf/0x20
</IRQ>
It was triggered by fuzzer but can be easily reproduced by:
# perf record -e cpu/branch-instructions/pu -g -c 1
Peter suggested not to allow branch tracing for precise events:
> Now arguably, this is really stupid behaviour. Who in his right mind
> wants callchain output on BTS entries. And even if they do, BTS +
> precise_ip is nonsensical.
>
> So in my mind disallowing precise_ip on BTS would be the simplest fix.
Suggested-by: Peter Zijlstra <pet...@infradead.org>
Fixes: 6cbc304f2f36 ("perf/x86/intel: Fix unwind errors from PEBS entries
(mk-II)")
Reported-by: Vince Weaver <vincent.wea...@maine.edu>
Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
arch/x86/events/intel/core.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 3fd3842571e8..284893373d69 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3102,6 +3102,10 @@ static int intel_pmu_bts_config(struct perf_event *event)
if (!attr->exclude_kernel)
return -EOPNOTSUPP;
+ /* BTS is not allowed for precise events. */
+ if (attr->precise_ip)
+ return -EOPNOTSUPP;
+
/* disallow bts if conflicting events are present */
if (x86_add_exclusive(x86_lbr_exclusive_lbr))
return -EBUSY;
--
2.17.2
