linux-kernel - Re: [PATCH v2] blkmq: Fix NULL pointer deref when all reserved tags in use

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Message-ID: <550A051F.3000106@kernel.dk>
Date:	Wed, 18 Mar 2015 17:07:11 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Sam Bradshaw <sbradshaw@...ron.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] blkmq: Fix NULL pointer deref when all reserved tags
 in use

On 03/18/2015 05:07 PM, Sam Bradshaw wrote:
> When allocating from the reserved tags pool, bt_get() is called with
> a NULL hctx.  If all tags are in use, the hw queue is kicked to push
> out any pending IO, potentially freeing tags, and tag allocation is
> retried.  The problem is that blk_mq_run_hw_queue() doesn't check for
> a NULL hctx.  So we avoid it with a simple NULL hctx test.
>
> This issue was introduced by:
> b32232073e80: blk-mq: fix hang in bt_get()
>
> Tested by hammering mtip32xx with concurrent smartctl/hdparm.
>
> Signed-off-by: Sam Bradshaw <sbradshaw@...ron.com>
> Signed-off-by: Selvan Mani <smani@...ron.com>

Thanks Sam, added to the current series.

-- 
Jens Axboe

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