linux-kernel - Re: [PATCH] blk-mq: bitmap tag: fix potential unwakeable sleep in bt

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Message-ID: <53CCCC76.7060506@kernel.dk>
Date:	Mon, 21 Jul 2014 10:16:54 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Alexander Gordeev <agordeev@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-mq: bitmap tag: fix potential unwakeable sleep in
 bt_get()

On 2014-07-21 10:10, Alexander Gordeev wrote:
> There is a race between __bt_get_word() and bt_clear_tag(). Since
> access to the tags bitmap is not serialized __bt_get_word() might
> miss a tag which is about to or being returned by bt_clear_tag().
> As result, the process requesting the tag might end up schedulled
> out forever.
>
> To avoid this corner case call io_schedule_timeout() instead of
> io_schedule(). The timeout should be long enough to not falsely
> wake up waiters often, so take the requests queue's "rq_timeout"
> for that.

What is this patch against?


-- 
Jens Axboe

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