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Commit 263b4509 authored by Scott Mayhew's avatar Scott Mayhew Committed by Trond Myklebust
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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 c7559663 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: default avatarScott Mayhew <smayhew@redhat.com>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
parent a9ab5e84

fs/nfs/write.c

+6 −5
Original line number Diff line number Diff line
@@ -922,19 +922,20 @@ out: 
 * 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;

}