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

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Message-ID: <5509F34C.3010404@kernel.dk>
Date:	Wed, 18 Mar 2015 15:51:08 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Sam Bradshaw <sbradshaw@...ron.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blkmq: Fix NULL pointer deref when all reserved tags
 in use

On 03/18/2015 03:06 PM, Sam Bradshaw wrote:
>
>> Good catch! But why not put the hctx == NULL check in as a conditional
>> in bt_get() before running the queue? I can't imagine other cases where
>> calling blk_mq_run_hw_queue() with hctx == NULL would be a valid
>> scenario.
>
> The change was meant to be broad in scope.  A runtime NULL deref is a
> rather unfortunate way to determine that there are other invalid scenarios.

Normally those kinds of issues would trigger quickly and it'd be 
obvious. Granted, this was an error handling case for the special case 
of reserved tags, so it persisted longer than it should have... But in 
general, I would not be too worried.

> But given that both approaches fix the immediate problem, I'd be happy
> to change the patch as you suggest.

Thanks!

-- 
Jens Axboe

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