linux-kernel - Re: [GIT] Please pull 2 NFS client fixes

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Date:	Thu, 07 Feb 2008 23:18:03 -0500
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	nfsv4@...ux-nfs.org
Subject: Re: [GIT] Please pull 2 NFS client fixes


On Thu, 2008-02-07 at 18:48 -0800, Andrew Morton wrote:
> On Thu, 07 Feb 2008 20:07:21 -0500 Trond Myklebust <Trond.Myklebust@...app.com> wrote:
> 
> > commit 5d47a35600270e7115061cb1320ee60ae9bcb6b8
> > Author: Trond Myklebust <Trond.Myklebust@...app.com>
> > Date:   Thu Feb 7 17:24:07 2008 -0500
> > 
> >     NFS: Fix a potential file corruption issue when writing
> >     
> >     If the inode is flagged as having an invalid mapping, then we can't rely on
> >     the PageUptodate() flag. Ensure that we don't use the "anti-fragmentation"
> >     write optimisation in nfs_updatepage(), since that will cause NFS to write
> >     out areas of the page that are no longer guaranteed to be up to date.
> >     
> >     A potential corruption could occur in the following scenario:
> >     
> >     client 1			client 2
> >     ===============			===============
> >     				fd=open("f",O_CREAT|O_WRONLY,0644);
> >     				write(fd,"fubar\n",6);	// cache last page
> >     				close(fd);
> >     fd=open("f",O_WRONLY|O_APPEND);
> >     write(fd,"foo\n",4);
> >     close(fd);
> >     
> >     				fd=open("f",O_WRONLY|O_APPEND);
> >     				write(fd,"bar\n",4);
> >     				close(fd);
> >     -----
> >     The bug may lead to the file "f" reading 'fubar\n\0\0\0\nbar\n' because
> >     client 2 does not update the cached page after re-opening the file for
> >     write. Instead it keeps it marked as PageUptodate() until someone calls
> >     invaldate_inode_pages2() (typically by calling read()).
> 
> Is this one worth feeding back into 2.6.24.x?  (for various values of "4"?)

Definitely, and probably back into 2.6.23.x, 2.6.22.x,... too.

Cheers
  Trond
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