xfs: reduce ilock hold times in xfs_file_aio_write_checks

We do not need the ilock for generic_write_checks and the i_size_read,
which are protected by i_mutex and/or iolock, so reduce the ilock
critical section to just the call to xfs_zero_eof.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 9 insertions, 14 deletions

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 54a67dd9ac0..3537c8d0af4 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -593,35 +593,31 @@ xfs_file_aio_write_checks(
         struct xfs_inode        *ip = XFS_I(inode);
         int                     error = 0;
 
-        xfs_rw_ilock(ip, XFS_ILOCK_EXCL);
 restart:
         error = generic_write_checks(file, pos, count, S_ISBLK(inode->i_mode));
-        if (error) {
-                xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
+        if (error)
                 return error;
-        }
 
         /*
          * If the offset is beyond the size of the file, we need to zero any
          * blocks that fall between the existing EOF and the start of this
          * write.  If zeroing is needed and we are currently holding the
-         * iolock shared, we need to update it to exclusive which involves
-         * dropping all locks and relocking to maintain correct locking order.
-         * If we do this, restart the function to ensure all checks and values
-         * are still valid.
+         * iolock shared, we need to update it to exclusive which implies
+         * having to redo all checks before.
          */
         if (*pos > i_size_read(inode)) {
                 if (*iolock == XFS_IOLOCK_SHARED) {
-                        xfs_rw_iunlock(ip, XFS_ILOCK_EXCL | *iolock);
+                        xfs_rw_iunlock(ip, *iolock);
                         *iolock = XFS_IOLOCK_EXCL;
-                        xfs_rw_ilock(ip, XFS_ILOCK_EXCL | *iolock);
+                        xfs_rw_ilock(ip, *iolock);
                         goto restart;
                 }
+                xfs_rw_ilock(ip, XFS_ILOCK_EXCL);
                 error = -xfs_zero_eof(ip, *pos, i_size_read(inode));
+                xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
+                if (error)
+                        return error;
         }
-        xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
-        if (error)
-                return error;
 
         /*
          * Updating the timestamps will grab the ilock again from
@@ -638,7 +634,6 @@ restart:
          * people from modifying setuid and setgid binaries.
          */
         return file_remove_suid(file);
-
 }
 
 /*