linux-kernel - Re: 2.6.21-rc suspend regression: sysfs deadlock

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Date:	Tue, 13 Mar 2007 16:09:57 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Hugh Dickins <hugh@...itas.com>
cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Oliver Neukum <oneukum@...e.de>,
	Maneesh Soni <maneesh@...ibm.com>, <gregkh@...e.de>,
	Richard Purdie <rpurdie@...ys.net>,
	James Bottomley <James.Bottomley@...elEye.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21-rc suspend regression: sysfs deadlock

On Tue, 13 Mar 2007, Hugh Dickins wrote:

> On Tue, 13 Mar 2007, Alan Stern wrote:
> > 
> > The consensus is that we would be better off keeping Oliver's original 
> > patch without your silly change, and instead fixing the particular method 
> > call that deadlocked.  Can you please try out the patch below with 
> > everything else as it was before?  It should solve your problem.
> 
> Yep, it works fine with your patch in and my silly reverted, thanks.
> But (I was about to say, even before seeing Cornelia's reply, honest!)
> I think you do need to check (audit the source? or is some runtime
> check possible?) for other such "suicidal" sysfs files, which
> seemed to (sysfs-ignorant) me to pose the real problem.

A runtime check wouldn't detect anything until someone tried to use the 
file -- at which point the process would deadlock anyway.

On the other hand, a quick survey of the kernel source shows that
DEVICE_ATTR is used over 1500 times.  Auditing all of them is not a job
for the faint-of-heart!

Alan Stern

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