From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <axboe@kernel.dk>
Subject: Re: [BUG] Deadlock in blk_mq_register_disk error path
To: Jinpu Wang <jinpu.wang@profitbricks.com>, linux-block@vger.kernel.org
References: <CAMGffEmw8ako59nAkDfpHWH06xAngkKR0YYpxF24LwZMjA9P2g@mail.gmail.com>
From: Jens Axboe <axboe@kernel.dk>
Message-ID: <16bc5b4f-e217-969e-4f26-5f4b04705dcc@kernel.dk>
Date: Tue, 2 Aug 2016 10:21:22 -0700
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On 08/02/2016 06:58 AM, Jinpu Wang wrote:
> Hi Jens,
>
> I found in blk_mq_register_disk, we blk_mq_disable_hotplug which in
> turn mutex_lock(&all_q_mutex);
>   queue_for_each_hw_ctx(q, hctx, i) {
>                 ret = blk_mq_register_hctx(hctx);
>                 if (ret)
>                         break; /// if about error out, we will call
> unregister below
>         }
>
>         if (ret)
>                 blk_mq_unregister_disk(disk);
>
> In blk_mq_unregister_disk, we will try to disable_hotplug again, which
> leads to dead lock.
>
> Did I miss anything?

Nope, your analysis looks correct. This should fix it:

http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=6316338a94b2319abe9d3790eb9cdc56ef81ac1a


-- 
Jens Axboe