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SubjectRe: [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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