Re: [PATCH 1/3] powerpc/perf: fix preempt count underflow in fsl_emb_pmu_del

[Shrikanth Hegde <sshegde@linux.ibm.com>]

On 5/18/26 10:38 AM, Aboorva Devarajan wrote:
> fsl_emb_pmu_del() unconditionally calls put_cpu_var(cpu_hw_events) at
> the 'out:' label, but only calls the matching get_cpu_var() after the
> 'i < 0' early-return check. When event->hw.idx is negative the
> function jumps to 'out:' without having taken get_cpu_var(), and the
> trailing put_cpu_var() then issues an unmatched preempt_enable(),
> underflowing preempt_count.
> 
> On a CONFIG_PREEMPT=y kernel preempt_count would underflow and
> eventually present as a 'scheduling while atomic' BUG.
> 
> Move put_cpu_var() to pair with get_cpu_var() so the percpu access is
> correctly bracketed and the 'out:' label only handles perf_pmu_enable.
> 
> Fixes: a11106544f33c ("powerpc/perf: e500 support")
> Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
> ---
>   arch/powerpc/perf/core-fsl-emb.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/perf/core-fsl-emb.c b/arch/powerpc/perf/core-fsl-emb.c
> index 7120ab20cbfec..02b5dd74c187a 100644
> --- a/arch/powerpc/perf/core-fsl-emb.c
> +++ b/arch/powerpc/perf/core-fsl-emb.c
> @@ -366,9 +366,10 @@ static void fsl_emb_pmu_del(struct perf_event *event, int flags)
>   
>   	cpuhw->n_events--;
>   
> +	put_cpu_var(cpu_hw_events);
> +
>    out:
>   	perf_pmu_enable(event->pmu);
> -	put_cpu_var(cpu_hw_events);
>   }
>   
>   static void fsl_emb_pmu_start(struct perf_event *event, int ef_flags)

Thanks for fixing this. Looks good to me.

Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>