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Date:   Thu, 12 Sep 2019 13:04:29 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Yu Zhao <yuzhao@google.com>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/4] mm: avoid slub allocation while holding list_lock
Message-ID: <20190912100429.fk5er66aostbtvyi@box>
References: <20190912004401.jdemtajrspetk3fh@box>
 <20190912023111.219636-1-yuzhao@google.com>
 <20190912023111.219636-3-yuzhao@google.com>
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On Wed, Sep 11, 2019 at 08:31:10PM -0600, Yu Zhao wrote:
> If we are already under list_lock, don't call kmalloc(). Otherwise we
> will run into deadlock because kmalloc() also tries to grab the same
> lock.
> 
> Fixing the problem by using a static bitmap instead.
> 
>   WARNING: possible recursive locking detected
>   --------------------------------------------
>   mount-encrypted/4921 is trying to acquire lock:
>   (&(&n->list_lock)->rlock){-.-.}, at: ___slab_alloc+0x104/0x437
> 
>   but task is already holding lock:
>   (&(&n->list_lock)->rlock){-.-.}, at: __kmem_cache_shutdown+0x81/0x3cb
> 
>   other info that might help us debug this:
>    Possible unsafe locking scenario:
> 
>          CPU0
>          ----
>     lock(&(&n->list_lock)->rlock);
>     lock(&(&n->list_lock)->rlock);
> 
>    *** DEADLOCK ***
> 
> Signed-off-by: Yu Zhao <yuzhao@google.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov