Re: [PATCH] kasan: Prevent cpu_quarantine corruption when CPU offline and cache shrink occur at same time

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 14 Apr 2022 10:59:25 +0800 Zqiang <qiang1.zhang@intel.com> wrote:

> The kasan_quarantine_remove_cache() is called in kmem_cache_shrink()/
> destroy(), the kasan_quarantine_remove_cache() call is protected by
> cpuslock in kmem_cache_destroy(), can ensure serialization with
> kasan_cpu_offline(). however the kasan_quarantine_remove_cache() call
> is not protected by cpuslock in kmem_cache_shrink(), when CPU going
> offline and cache shrink occur at same time, the cpu_quarantine may be
> corrupted by interrupt(per_cpu_remove_cache operation). so add
> cpu_quarantine offline flags check in per_cpu_remove_cache().
> 
> ...
>

Could we please have some reviewer input here?

> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -330,6 +330,8 @@ static void per_cpu_remove_cache(void *arg)
>  	struct cpu_shrink_qlist *sq;
>  #endif
>  	q = this_cpu_ptr(&cpu_quarantine);
> +	if (READ_ONCE(q->offline))
> +		return;
>  #ifndef CONFIG_PREEMPT_RT
>  	qlist_move_cache(q, &to_free, cache);
>  	qlist_free_all(&to_free, cache);

It might be helpful to have a little comment which explains why we're
doing this?