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

[Mark Fasheh]

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.
	--Mark

--
Mark Fasheh