linux-kernel - Re: [PATCH 1/3] fuse/dev: Fix unbalanced calls to kunmap

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Date:	Mon, 21 Jul 2014 07:18:54 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	lxc-devel@...ts.linuxcontainers.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	"Michael H. Warfield" <mhw@...tsend.com>,
	Seth Forshee <seth.forshee@...onical.com>
Subject: Re: [PATCH 1/3] fuse/dev: Fix unbalanced calls to kunmap_atomic()
 during splice I/O

On Fri, Jul 18, 2014 at 05:21:55PM +0200, Miklos Szeredi wrote:
> On Mon, Jul 14, 2014 at 9:18 PM, Seth Forshee
> <seth.forshee@...onical.com> wrote:
> > fuse_copy_finish() assumes that mapaddr in fuse_copy_state refers
> > to a valid mapping if currbuf is non-NULL, but this isn't always
> > true when moving pages for splice I/O. This results in an
> > unbalanced call to kunmap_atomic() and thus an unbalanced
> > decrement of the preempt count. Avoid this by checking that
> > mapaddr is non-NULL before calling kunmap_atomic().
> 
> I guess this is obsoleted by:
> 
>   c55a01d360af  fuse: avoid scheduling while atomic
> 
> which moves the kmap/kunmap closer to the actual use of the mapping.
> 
> Can you please verify?

Yes, that commit does seem to fix the problem.

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