linux-kernel - Re: [PATCH 0/5] locks: move most locks_release_private calls outside of i

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Date:	Tue, 12 Aug 2014 13:53:03 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Jeff Layton <jeff.layton@...marydata.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-nfs@...r.kernel.org, trond.myklebust@...marydata.com
Subject: Re: [PATCH 0/5] locks: move most locks_release_private calls outside
 of i_lock

On Tue, Aug 12, 2014 at 01:43:13PM -0400, Jeff Layton wrote:
> On Tue, 12 Aug 2014 10:48:08 -0400
> Jeff Layton <jlayton@...marydata.com> wrote:
> 
> > In the days of yore, the file locking code was primarily protected by
> > the BKL. That changed in commit 72f98e72551fa (locks: turn lock_flocks
> > into a spinlock), at which point the code was changed to be protected
> > by a conventional spinlock (mostly due to a push to finally eliminate
> > the BKL). Since then, the code has been changed to use the i_lock
> > instead of a global spinlock, but it's still under a spinlock.
> > 
> > With that change, several functions now no longer can block when they
> > originally could. This is a particular problem with the
> > fl_release_private operation. In NFSv4, that operation is used to kick
> > off a RELEASE_LOCKOWNER or FREE_STATEID call, and that requires being
> > able to do an allocation.
> > 
> > This was reported by Josh Stone here:
> > 
> >     https://bugzilla.redhat.com/show_bug.cgi?id=1089092
> > 
> > My initial stab at fixing this involved moving this to a workqueue, but
> > Trond pointed out the above change was technically a regression with the
> > way the spinlocking in the file locking code works, and suggested an
> > alternate approach to fixing it.
> > 
> > This set focuses on moving most of the locks_release_private calls
> > outside of the inode->i_lock. There are still a few that are done
> > under the i_lock in the lease handling code. Cleaning up the use of
> > the i_lock in the lease code is a larger project which we'll have to
> > tackle at some point, but there are some other cleanups that will
> > need to happen first.
> > 
> > Absent any objections, I'll plan to merge these for 3.18.
> > 
> 
> Erm...make that v3.17...
> 
> As Trond points out, the fact that we end up doing sleeping allocations
> under spinlock can allow an unprivileged user to crash a NFSv4 client.
> So I may see about merging these sooner rather than later after they've
> had a little soak time in linux-next.

Looks reasonable to me--ACK on the set.

--b.
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