[PATCH 2/5] 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@...>

---
 fs/xfs/xfs_file.c |   23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

Index: xfs/fs/xfs/xfs_file.c
===================================================================
--- xfs.orig/fs/xfs/xfs_file.c 2012-03-26 21:22:01.495953714 +0200
+++ xfs/fs/xfs/xfs_file.c 2012-03-26 21:24:07.955268625 +0200
@@ -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);
-
 }
 
 /*

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