linux-kernel - Re: [PATCH V1] elevator: Fix a race about elevator switching.

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Date:	Wed, 3 Jul 2013 13:25:44 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	majianpeng <majianpeng@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V1] elevator: Fix a race about elevator switching.

On Mon, Jul 01 2013, majianpeng wrote:
> Thare's a race between elevator switching and normal io operation.
>     Because the allocation of struct elevator_queue and struct elevator_data
>     don't in a atomic operation.So there are have chance to use NULL
>     ->elevator_data.
>     For example:
>         Thread A:                               Thread B
>         blk_queu_bio                            elevator_switch
>         spin_lock_irq(q->queue_block)           elevator_alloc
>         elv_merge                               elevator_init_fn
>     
>     Because call elevator_alloc, it can't hold queue_lock and the
>     ->elevator_data is NULL.So at the same time, threadA call elv_merge and
>     nedd some info of elevator_data.So the crash happened.
>     
>     Move the elevator_alloc into func elevator_init_fn, it make the
>     operations in a atomic operation.
>     
>     Using the follow method can easy reproduce this bug
>     1:dd if=/dev/sdb of=/dev/null
>     2:while true;do echo noop > scheduler;echo deadline > scheduler;done
>     
>     The test method also use this method.

Applied, thanks.

-- 
Jens Axboe

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