[XFS] Fix race in xfs_write() between direct and buffered I/O with DMAPI

The iolock is dropped and re-acquired around the call to XFS_SEND_NAMESP().
While the iolock is released the file can become cached.  We then
'goto retry' and - if we are doing direct I/O - mapping->nrpages may now be
non zero but need_i_mutex will be zero and we will hit the WARN_ON().

Since we have dropped the I/O lock then the file size may have also changed
so what we need to do here is 'goto start' like we do for the XFS_SEND_DATA()
DMAPI event.

We also need to update the filesize before releasing the iolock so that
needs to be done before the XFS_SEND_NAMESP event.  If we drop the iolock
before setting the filesize we could race with a truncate.

Reviewed-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

1 files changed, 12 insertions, 15 deletions

diff --git a/fs/xfs/linux-2.6/xfs_lrw.c b/fs/xfs/linux-2.6/xfs_lrw.c
index 92ce34b3787a..7e90daa0d1d1 100644
--- a/fs/xfs/linux-2.6/xfs_lrw.c
+++ b/fs/xfs/linux-2.6/xfs_lrw.c
@@ -707,7 +707,6 @@ start:
                 }
         }
 
-retry:
         /* We can write back this queue in page reclaim */
         current->backing_dev_info = mapping->backing_dev_info;
 
@@ -763,6 +762,17 @@ retry:
         if (ret == -EIOCBQUEUED && !(ioflags & IO_ISAIO))
                 ret = wait_on_sync_kiocb(iocb);
 
+        isize = i_size_read(inode);
+        if (unlikely(ret < 0 && ret != -EFAULT && *offset > isize))
+                *offset = isize;
+
+        if (*offset > xip->i_size) {
+                xfs_ilock(xip, XFS_ILOCK_EXCL);
+                if (*offset > xip->i_size)
+                        xip->i_size = *offset;
+                xfs_iunlock(xip, XFS_ILOCK_EXCL);
+        }
+
         if (ret == -ENOSPC &&
             DM_EVENT_ENABLED(xip, DM_EVENT_NOSPACE) && !(ioflags & IO_INVIS)) {
                 xfs_iunlock(xip, iolock);
@@ -776,20 +786,7 @@ retry:
                 xfs_ilock(xip, iolock);
                 if (error)
                         goto out_unlock_internal;
-                pos = xip->i_size;
-                ret = 0;
-                goto retry;
-        }
-
-        isize = i_size_read(inode);
-        if (unlikely(ret < 0 && ret != -EFAULT && *offset > isize))
-                *offset = isize;
-
-        if (*offset > xip->i_size) {
-                xfs_ilock(xip, XFS_ILOCK_EXCL);
-                if (*offset > xip->i_size)
-                        xip->i_size = *offset;
-                xfs_iunlock(xip, XFS_ILOCK_EXCL);
+                goto start;
         }
 
         error = -ret;