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nfs: always make sure page is up-to-date before extending a write to …

…cover the entire page

We should always make sure the cached page is up-to-date when we're
determining whether we can extend a write to cover the full page -- even
if we've received a write delegation from the server.

Commit c755966 added logic to skip this check if we have a write
delegation, which can lead to data corruption such as the following
scenario if client B receives a write delegation from the NFS server:

Client A:
    # echo 123456789 > /mnt/file

Client B:
    # echo abcdefghi >> /mnt/file
    # cat /mnt/file
    0�D0�abcdefghi

Just because we hold a write delegation doesn't mean that we've read in
the entire page contents.

Cc: <stable@vger.kernel.org> # v3.11+
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
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scottmayhew authored and trondmypd committed Jan 17, 2014
1 parent a9ab5e8 commit 263b4509ec4d47e0da3e753f85a39ea12d1eff24
Showing with 6 additions and 5 deletions.
  1. +6 −5 fs/nfs/write.c
@@ -922,19 +922,20 @@ static bool nfs_write_pageuptodate(struct page *page, struct inode *inode)
* extend the write to cover the entire page in order to avoid fragmentation
* inefficiencies.
*
* If the file is opened for synchronous writes or if we have a write delegation
* from the server then we can just skip the rest of the checks.
* If the file is opened for synchronous writes then we can just skip the rest
* of the checks.
*/
static int nfs_can_extend_write(struct file *file, struct page *page, struct inode *inode)
{
if (file->f_flags & O_DSYNC)
return 0;
if (!nfs_write_pageuptodate(page, inode))
return 0;
if (NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
return 1;
if (nfs_write_pageuptodate(page, inode) && (inode->i_flock == NULL ||
(inode->i_flock->fl_start == 0 &&
if (inode->i_flock == NULL || (inode->i_flock->fl_start == 0 &&
inode->i_flock->fl_end == OFFSET_MAX &&
inode->i_flock->fl_type != F_RDLCK)))
inode->i_flock->fl_type != F_RDLCK))
return 1;
return 0;
}

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