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Re: [Xen-devel] [PATCH] Fix blkback/blktap sysfs read bug.

To: Joe Jin <joe.jin@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Fix blkback/blktap sysfs read bug.
From: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Date: Thu, 21 Jan 2010 10:01:44 -0800
Cc: "greg.marsden@xxxxxxxxxx" <greg.marsden@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "deepak.patel@xxxxxxxxxx" <deepak.patel@xxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
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On Thu, 2010-01-21 at 02:49 -0500, Joe Jin wrote:

> > The reason is in sysfs_deactivate(), which will sync callers against any
> > remaining thread in .show()
> > - show() hangs on the lock
> > - the lock holder in sysfs_remove_group(), 
> >   waiting for show() to complete.
> > 
> > Pardon me -- I'm not entirely sure where/how these patches are currently
> > submitted and merged. I suppose yours are only for linux-2.6.18.hg, not
> > e.g. pvops? Then sorry for any confusion.
> > 
> Daniel, 
> Thanks a lot of your comments, it really help for me, yes my patch based 
> linux-2.6.18.hg branch. As Jan have pointed out in previous email, it should 
> be sysfs's issue, looked like later kernel sysfs have fixed the issue?

Yes. Later sysfs won't need the locking. Ordering sysfs removal before
backend release will be sufficient.


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