linux-kernel - Re: [PATCH RESEND 2/3 v2.6.39-rc7] block: make disk_block_events() properly wait for work cancellation

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Date:	Wed, 18 May 2011 12:04:51 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Jens Axboe <axboe@...nel.dk>, Sitsofe Wheeler <sitsofe@...oo.com>,
	Borislav Petkov <bp@...en8.de>, Meelis Roos <mroos@...ux.ee>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND 2/3 v2.6.39-rc7] block: make disk_block_events()
 properly wait for work cancellation

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
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