Re: [PATCH 1/2] perf/x86/intel: Only check the group flag for X86 leader

[Peter Zijlstra]

On Wed, Apr 23, 2025 at 03:10:14PM -0700, kan.liang@xxxxxxxxxxxxxxx wrote:
> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> 
> A warning in intel_pmu_lbr_counters_reorder() may be triggered by below
> perf command.
> 
> perf record -e "{cpu-clock,cycles/call-graph="lbr"/}" -- sleep 1
> 
> It's because the group is mistakenly treated as a branch counter group.
> 
> The hw.flags of the leader are used to determine whether a group is a
> branch counters group. However, the hw.flags is only available for a
> hardware event. The field to store the flags is a union type. For a
> software event, it's a hrtimer. The corresponding bit may be set if the
> leader is a software event.
> 
> For a branch counter group and other groups that have a group flag
> (e.g., topdown, PEBS counters snapshotting, and ACR), the leader must
> be a X86 event. Check the X86 event before checking the flag.
> 
> There may be an alternative way to fix the issue by moving the hw.flags
> out of the union type. It should work for now. But it's still possible
> that the flags will be used by other types of events later. As long as
> that type of event is used as a leader, a similar issue will be
> triggered. So the alternative way is dropped.
> 
> Reported-by: Luo Gengkun <luogengkun@xxxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/lkml/20250412091423.1839809-1-luogengkun@xxxxxxxxxxxxxxx/
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

Can I get a Fixes tag for this such that I can stick it in urgent?