diff options
| author | Peter Zijlstra | 2022-10-04 12:20:39 +0200 |
|---|---|---|
| committer | Peter Zijlstra | 2022-10-04 13:32:09 +0200 |
| commit | 82aad7ff7ac25c8cf09d491ae23b9823f1901486 (patch) | |
| tree | 91133f2c55e578b0c8398f2e3b4c7964c1746c7a /kernel/events | |
| parent | 7be51cc1c68dfa180ef84e71bcb4204237bb5620 (diff) | |
perf/hw_breakpoint: Annotate tsk->perf_event_mutex vs ctx->mutex
Perf fuzzer gifted a lockdep splat:
perf_event_init_context()
mutex_lock(parent_ctx->mutex); (B)
inherit_task_group()
inherit_group()
inherit_event()
perf_event_alloc()
perf_try_init_event() := hw_breakpoint_event_init()
register_perf_hw_breakpoint()
mutex_lock(child->perf_event_mutex); (A)
Which is against the normal (documented) order. Now, this is a false
positive in that child is not published yet, but also inherited events
never end up on ->perf_event_list.
Annotate this one away.
Fixes: 0912037fec11 ("perf/hw_breakpoint: Reduce contention with large number of tasks")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Diffstat (limited to 'kernel/events')
| -rw-r--r-- | kernel/events/hw_breakpoint.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c index 7ef0e98d31e2..c3797701339c 100644 --- a/kernel/events/hw_breakpoint.c +++ b/kernel/events/hw_breakpoint.c @@ -117,7 +117,17 @@ static struct mutex *bp_constraints_lock(struct perf_event *bp) struct mutex *tsk_mtx = get_task_bps_mutex(bp); if (tsk_mtx) { - mutex_lock(tsk_mtx); + /* + * Fully analogous to the perf_try_init_event() nesting + * argument in the comment near perf_event_ctx_lock_nested(); + * this child->perf_event_mutex cannot ever deadlock against + * the parent->perf_event_mutex usage from + * perf_event_task_{en,dis}able(). + * + * Specifically, inherited events will never occur on + * ->perf_event_list. + */ + mutex_lock_nested(tsk_mtx, SINGLE_DEPTH_NESTING); percpu_down_read(&bp_cpuinfo_sem); } else { percpu_down_write(&bp_cpuinfo_sem); |