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

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Message-Id: <20220421150746.627e0f62363485d65c857010@linux-foundation.org>
Date:   Thu, 21 Apr 2022 15:07:46 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     ryabinin.a.a@...il.com, dvyukov@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] kasan: Prevent cpu_quarantine corruption when CPU
 offline and cache shrink occur at same time

On Thu, 14 Apr 2022 10:59:25 +0800 Zqiang <qiang1.zhang@...el.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?