linux-kernel - Re: Bug in disk event polling

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Message-ID: <20120210211255.GK19392@google.com>
Date:	Fri, 10 Feb 2012 13:12:55 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Jens Axboe <axboe@...nel.dk>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Linux-pm mailing list <linux-pm@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Bug in disk event polling

Hello, Alan.

On Fri, Feb 10, 2012 at 04:03:51PM -0500, Alan Stern wrote:
> None of those resets above should have occurred.  They are the result
> of trying to recover from the failure of a TEST UNIT READY command.

Thanks for the log.  Yeah, I was just thinking about libata and
wondering why it would break that badly.

> > > I have verified that changing all occurrences of system_nrt_wq in 
> > > block/genhd.c to system_freezable_wq fixes the bug.  However this may 
> > > not be the way you want to solve it; you may prefer to have a freezable 
> > > non-reentrant work queue.
> > 
> > Please feel free to send out a patch to fix the issue. :)
> 
> Is there a real reason for using system_nrt_wq?  Are you okay with just
> switching over to system_freezable_wq?

I think it should be nrt.  It assumes that no one else is running it
concurrently; otherwise, multiple CPUs could jump into
disk->fops->check_events() concurrently which can be pretty ugly.

Thanks.

-- 
tejun
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