Re: [PATCH v2] libperf: Handle an evsel without an fd array in enable/disable

[sashiko-bot@kernel.org]

> A group led by a tool PMU event is opened with the members' group_fd set
> to the leader's file descriptor.  For a tool event that descriptor comes
> from open("/proc/stat"), not from perf_event_open(), so a member the
> kernel refuses is marked unsupported; perf stat then releases the fd
> array of that member while the evsel stays in the group.
> 
> Enabling the group goes through evsel__enable_cpu(), which enables the
> members of a mixed PMU group from userspace because the kernel does not
> do it along with the leader.  The member has no fd array left, so
> perf_evsel__run_ioctl() reads its loop bound through xyarray__max_y()
> and dereferences a NULL pointer:
> 
>   $ perf stat -a -e '{user_time,cycles}' -- sleep 0.05
>   Segmentation fault
> 
> [ ... ]
> Fixes: 0b18bced5444 ("perf tool_pmu: Make tool PMU events respect enable/disable")
> Link: https://lore.kernel.org/avQIOtt7Y67oXQem@z2
> Suggested-by: Namhyung Kim <namhyung@kernel.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: TAKANO Mitsuhiro <takano32@gmail.com>

Sashiko has reviewed this patch and found no issues.

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