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Date: Wed, 18 May 2011 12:04:51 +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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Hello,

On Wed, May 18, 2011 at 02:46:30AM -0700, Linus Torvalds wrote:
> Quite frankly. right now I think I need to just release 2.6.39, and
> then for 2.6.40 merge the trivial
> 
>   mutex_lock(&ev->mutex);
>   if (!ev->block++)
>     cancel_delayed_work_sync(&ev->dwork);
>   mutex_unlock(&ev->mutex);
> 
> with a cc: stable for backporting.

This isn't super-critical and releasing without the fix but later
backporting via -stable definitely is an option.

> So we can't be in some atomic context inside some other spinlock
> anyway, afaik. And there can be no lock order issues, since this
> would always be a new inner lock.

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.

Thanks.

-- 
tejun