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Date: Wed, 18 May 2011 13:07:32 +0200
From: Tejun Heo <tj@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>, Sitsofe Wheeler <sitsofe@yahoo.com>,
        Borislav Petkov <bp@alien8.de>, Meelis Roos <mroos@linux.ee>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kay Sievers <kay.sievers@vrfy.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RESEND 2/3 v2.6.39-rc7] block: make disk_block_events()
 properly wait for work cancellation
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On Wed, May 18, 2011 at 12:04:51PM +0200, Tejun Heo wrote:
> Yeap, the problem was unblock/check being allowed to be called without
> sleeping context, which isn't used anymore and was broken due to
> cancellation race.  We can just enclose the whole thing inside per-ev
> mutex and everything should be simple and fine.  I'll post patches
> soon.

Oops, spoke too soon.  Converting to mutex creates a circular
dependency.  disk_block_events() acquires ev->lock and waits for
ev->dwork to finish, but ev->dwork also needs to acquire ev->lock to
update event states.  So, no matter how we twist this, we need two
locks or a lock and a completion.  The mutex approach seems simple
enough, so I suggest leaving it like that.

Thanks.

-- 
tejun