Re: [PATCH] perf/x86: Don't WARN when the ext_regs_buf allocation fails

[sashiko-bot@kernel.org]

> reserve_ext_regs_buffers() wraps the per-CPU ext_regs_buf allocation in
> WARN_ON_ONCE(). The allocator already prints a warning with a stack dump
> when a GFP_KERNEL allocation fails, so the WARN only repeats it, which
> Documentation/process/coding-style.rst asks not to do. The failure is
> also handled: the buffers are freed again, the event is still created,
> and events that ask for SIMD or extended register sampling are rejected
> with -ENOMEM in x86_pmu_hw_config() and event_simd_regs_validate().
> 
> syzkaller hit this with fault injection on next-20261002. The trigger
> is a plain hardware cycles event opened while no other x86 PMU event
> exists, with the allocation failed:
> 
>   !per_cpu(ext_regs_buf, cpu)
>   WARNING: arch/x86/events/core.c:441 at reserve_ext_regs_buffers arch/x86/events/core.c:441 [inline]
>   WARNING: arch/x86/events/core.c:441 at x86_reserve_hardware+0x6ff/0x880 arch/x86/events/core.c:458
> [ ... ]
> warning.
> 
> Fixes: b84c96283684 ("perf/x86: Enable XMM register sampling for non-PEBS events")
> Assisted-by: Claude:claude-opus-5-5 syzkaller
> Signed-off-by: vineash <vineash30640@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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