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[PATCH 069/102] xfs: reduce ilock hold times in xfs_file_aio_write_check

To: xfs@xxxxxxxxxxx
Subject: [PATCH 069/102] xfs: reduce ilock hold times in xfs_file_aio_write_checks
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 23 Aug 2012 15:02:27 +1000
In-reply-to: <1345698180-13612-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1345698180-13612-1-git-send-email-david@xxxxxxxxxxxxx>
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>

Upstream commit: 467f78992a0743e0e71729e4faa20b67b0f25289

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@xxxxxx>
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>
Signed-off-by: Ben Myers <bpm@xxxxxxx>
---
 fs/xfs/linux-2.6/xfs_file.c |   23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index 1dbd1d8..d0239cf 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -589,35 +589,31 @@ 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
@@ -634,7 +630,6 @@ restart:
         * people from modifying setuid and setgid binaries.
         */
        return file_remove_suid(file);
-
 }
 
 /*
-- 
1.7.10

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