linux-kernel - Re: [PATCH] fat: Fix non-atomic NFS i

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Date:	Fri, 29 Jun 2012 13:19:34 -0500
From:	"Steven J. Magnani" <steve@...idescorp.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fat: Fix non-atomic NFS i_pos read

On Sat, 2012-06-30 at 03:06 +0900, OGAWA Hirofumi wrote: 
> "Steven J. Magnani" <steve@...idescorp.com> writes:
> 
> > fat_encode_fh() can fetch an invalid i_pos value on systems
> > where 64-bit accesses are not atomic. Make it use the same
> > accessor as the rest of the FAT code.
> >
> > Signed-off-by: Steven J. Magnani <steve@...idescorp.com>
> > ---
> > diff -uprN linux-3.5-rc4/fs/fat/inode.c new/fs/fat/inode.c
> > --- linux-3.5-rc4/fs/fat/inode.c	2012-06-29 11:20:12.781348652 -0500
> > +++ new/fs/fat/inode.c	2012-06-29 11:25:29.484713183 -0500
> > @@ -738,22 +738,22 @@ static int
> >  fat_encode_fh(struct inode *inode, __u32 *fh, int *lenp, struct inode *parent)
> >  {
> >  	int len = *lenp;
> > -	u32 ipos_h, ipos_m, ipos_l;
> > +	struct super_block *sb = inode->i_sb;
> > +	struct msdos_sb_info *sbi = MSDOS_SB(sb);
> 
> sb seems to be unused. So, we can just
> 
> 	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
> 
> true? Otherwise, ack.
OK, I'll repost with that change.

> 
> Acked-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
> 
> Just curious, this happened on the real system? I recently heard about
> NFS issue.
Not that I'm aware of. Can you point me to any discussion of the NFS
issue? I've spent a lot of time recently studying the FAT NFS
implementation and come to the conclusion that it is extremely
vulnerable to inode eviction.  More to follow...

Regards,
Steve


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