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Commit 557f7ad0 authored by Mark Rutland's avatar Mark Rutland Committed by Greg Kroah-Hartman
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perf: Fix perf_event_validate_size() lockdep splat

commit 7e2c1e4b upstream.

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: 382c27f4 ("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: default avatarLucas De Marchi <lucas.demarchi@intel.com>
Reported-by: default avatarPengfei Xu <pengfei.xu@intel.com>
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20231215112450.3972309-1-mark.rutland@arm.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a684235d
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