Re: [PATCH] panic: stop CPUs that lose the panic_redirect_cpu race

[Andrew Morton]

On Tue,  7 Jul 2026 17:22:52 +0000 Bradley Morgan <include@xxxxxxxxx> wrote:

> Loser of the redirect cmpxchg must stop, not fall through to
> panic_try_start().
> 
> This issue was found by sashiko [1].
> 
> [1] https://sashiko.dev/#/patchset/20260705164123.18746-1-include%40grrlz.net
> 
> ...
>
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -400,12 +400,9 @@ static bool panic_try_force_cpu(const char *fmt, va_list args)
>  	if (panic_in_progress())
>  		return false;
>  
> -	/*
> -	 * Only one CPU can do the redirect. Use atomic cmpxchg to ensure
> -	 * we don't race with another CPU also trying to redirect.
> -	 */
> +	/* Only one CPU redirects, the loser stops and lets it finish. */
>  	if (!atomic_try_cmpxchg(&panic_redirect_cpu, &old_cpu, this_cpu))
> -		return false;
> +		return true;
>  
>  	/*
>  	 * Use dynamically allocated buffer if available, otherwise

Sashiko is at it again:
	https://sashiko.dev/#/patchset/20260707172252.4842-1-include@xxxxxxxxx