lkml.org 
[lkml]   [2023]   [Dec]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip: perf/urgent] perf: Fix perf_event_validate_size() lockdep splat
The following commit has been merged into the perf/urgent branch of tip:

Commit-ID: 7e2c1e4b34f07d9aa8937fab88359d4a0fce468e
Gitweb: https://git.kernel.org/tip/7e2c1e4b34f07d9aa8937fab88359d4a0fce468e
Author: Mark Rutland <mark.rutland@arm.com>
AuthorDate: Fri, 15 Dec 2023 11:24:50
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 15 Dec 2023 12:33:23 +01:00

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
---
kernel/events/core.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index c9d123e..9efd0d7 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)
\
 
 \ /
  Last update: 2023-12-15 12:44    [W:0.049 / U:1.596 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site