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authorMark Rutland <mark.rutland@arm.com>2023-12-15 11:24:50 +0000
committerPeter Zijlstra <peterz@infradead.org>2023-12-15 12:33:23 +0100
commit7e2c1e4b34f07d9aa8937fab88359d4a0fce468e (patch)
tree3fe66c682b97c9107d8e20883053231ad922a0d9
parenta39b6ac3781d46ba18193c9dbb2110f31e9bffe9 (diff)
perf: Fix perf_event_validate_size() lockdep splat
When lockdep is enabled, the for_each_sibling_event(sibling, event) macro checks that event->ctx->mutex is held. When creating a new group leader event, we call perf_event_validate_size() on a partially initialized event where event->ctx is NULL, and so when for_each_sibling_event() attempts to check event->ctx->mutex, we get a splat, as reported by Lucas De Marchi: WARNING: CPU: 8 PID: 1471 at kernel/events/core.c:1950 __do_sys_perf_event_open+0xf37/0x1080 This only happens for a new event which is its own group_leader, and in this case there cannot be any sibling events. Thus it's safe to skip the check for siblings, which avoids having to make invasive and ugly changes to for_each_sibling_event(). Avoid the splat by bailing out early when the new event is its own group_leader. Fixes: 382c27f4ed28f803 ("perf: Fix perf_event_validate_size()") Closes: https://lore.kernel.org/lkml/20231214000620.3081018-1-lucas.demarchi@intel.com/ Closes: https://lore.kernel.org/lkml/ZXpm6gQ%2Fd59jGsuW@xpf.sh.intel.com/ Reported-by: Lucas De Marchi <lucas.demarchi@intel.com> Reported-by: Pengfei Xu <pengfei.xu@intel.com> Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20231215112450.3972309-1-mark.rutland@arm.com
-rw-r--r--kernel/events/core.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index c9d123e13b57..9efd0d7775e7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1947,6 +1947,16 @@ static bool perf_event_validate_size(struct perf_event *event)
group_leader->nr_siblings + 1) > 16*1024)
return false;
+ /*
+ * When creating a new group leader, group_leader->ctx is initialized
+ * after the size has been validated, but we cannot safely use
+ * for_each_sibling_event() until group_leader->ctx is set. A new group
+ * leader cannot have any siblings yet, so we can safely skip checking
+ * the non-existent siblings.
+ */
+ if (event == group_leader)
+ return true;
+
for_each_sibling_event(sibling, group_leader) {
if (__perf_event_read_size(sibling->attr.read_format,
group_leader->nr_siblings + 1) > 16*1024)