[Ocfs2-devel] [PATCH] ocfs2: llseek requires to ocfs2 inode lock for the file in SEEK_END

[Joel Becker]

On Tue, Jul 02, 2013 at 12:58:26PM -0700, Mark Fasheh wrote:
> On Mon, Jul 01, 2013 at 09:38:31AM +0800, Jensen wrote:
> > On 2013/6/29 21:37, Joel Becker wrote:
> > 
> > > On Thu, Jun 20, 2013 at 04:23:59PM +0800, shencanquan wrote:
> > >> llseek requires ocfs2 inode lock for updating the file size in SEEK_END.
> > >> because the file size maybe update on another node.
> > >> if it not . after call llseek in SEEK_END. the position is old.
> > >>
> > >> this bug can be reproduce the following scenario:
> > >> at first ,we dd a test fileA,the file size is 10k.
> > >> on NodeA:
> > >> ---------
> > >> 1) open the test fileA, lseek the end of file. and print the position.
> > >> 2) close the test fileA
> > >>
> > >> on NodeB:
> > >> 1) open the test fileA, append the 5k data to test FileA.
> > >> 2) lseek the end of file. and print the position.
> > >> 3) close file.
> > >>
> > >> at first we run the test program1 on NodeA , the result is 10k.
> > >> and then run the test program2 on NodeB,  the result is 15k.
> > >> at last, we run the test program1 on NodeA again, the result is 10k.
> > >>
> > >> after apply this patch.  the three step result is 15k.
> > >>
> > >> Signed-off-by: jensen <shencanquan at huawei.com>
> > >> ---
> > >>  fs/ocfs2/file.c |    9 +++++++++
> > >>  1 file changed, 9 insertions(+)
> > >>
> > >> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> > >> index ff54014..3afd24c 100644
> > >> --- a/fs/ocfs2/file.c
> > >> +++ b/fs/ocfs2/file.c
> > >> @@ -2626,7 +2626,16 @@ static loff_t ocfs2_file_llseek(struct file *file, loff_t offset, int whence)
> > >>  	case SEEK_SET:
> > >>  		break;
> > >>  	case SEEK_END:
> > >> +		/* SEEK_END requires the OCFS2 inode lock for the file
> > >> +		 * because it references the file's size.
> > >> +		 */
> > >> +		ret = ocfs2_inode_lock(inode, NULL, 0);
> > >> +		if (ret < 0) {
> > >> +			mlog_errno(ret);
> > >> +			goto out;
> > >> +		}
> > >>  		offset += inode->i_size;
> > >> +		ocfs2_inode_unlock(inode, 0);
> > > 
> > > Why wouldn't ocfs2_rw_lock() work?  Just because we dont get the LVB
> > > from it?
> > > 
> > 
> > 
> > Yes. we want to update the inode size from lvb.
> > 
> > I also think the file size maybe protected by inode lock. not rw lock.
> 
> Correct, if you want to get the most up to date i_size you'll have to be
> holding the meta (inode) lock.

Ok, then:

Acked-by: Joel Becker <jlbec at evilplan.org>

> 	--Mark
> 
> --
> Mark Fasheh
> 
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