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Re: [PATCH] fs: push i_mutex and filemap_write_and_wait down into ->fsyn

To: Josef Bacik <josef@xxxxxxxxxx>
Subject: Re: [PATCH] fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers
From: Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>
Date: Sat, 23 Jul 2011 21:32:25 +0200
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, hch@xxxxxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, jack@xxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
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In-reply-to: <20110723180942.GA1616@xxxxxxxxxxxxxx>
References: <1309370716-12235-1-git-send-email-josef@xxxxxxxxxx> <20110723180942.GA1616@xxxxxxxxxxxxxx>
On 2011.07.23 at 20:09 +0200, Markus Trippelsdorf wrote:
> On 2011.06.29 at 14:05 -0400, Josef Bacik wrote:
> > Btrfs needs to be able to control how filemap_write_and_wait_range() is 
> > called
> > in fsync to make it less of a painful operation, so push down taking 
> > i_mutex and
> > the calling of filemap_write_and_wait() down into the ->fsync() handlers.  
> > Some
> > file systems can drop taking the i_mutex altogether it seems, like ext3 and
> > ocfs2.  For correctness sake I just pushed everything down in all cases to 
> > make
> > sure that we keep the current behavior the same for everybody, and then each
> > individual fs maintainer can make up their mind about what to do from there.
> 
> At least the xfs part of this patch is broken.
> Running the latest git-kernel bogofilter doesn't work anymore on my xfs
> partition. When I run "bogoutil -d wordlist.db" to dump the contents of
> the database, it produces no output at all. 
> 
> Reverting 02c24a82187d (or only the xfs part of that commit) "solves"
> the problem.

Looks like a locking problem (note the stale xfs_rw_ilock):

diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index 7f782af..fbbf657 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -127,6 +127,8 @@ xfs_iozero(
 STATIC int
 xfs_file_fsync(
        struct file             *file,
+       loff_t                  start,
+       loff_t                  end,
        int                     datasync)
 {
        struct inode            *inode = file->f_mapping->host;
@@ -138,6 +140,10 @@ xfs_file_fsync(
 
        trace_xfs_file_fsync(ip);
 
+       error = filemap_write_and_wait_range(inode->i_mapping, start, end);
+       if (error)
+               return error;
+
        if (XFS_FORCED_SHUTDOWN(mp))
                return -XFS_ERROR(EIO);
 
@@ -875,18 +881,11 @@ xfs_file_aio_write(
        /* Handle various SYNC-type writes */
        if ((file->f_flags & O_DSYNC) || IS_SYNC(inode)) {
                loff_t end = pos + ret - 1;
-               int error, error2;
 
                xfs_rw_iunlock(ip, iolock);
-               error = filemap_write_and_wait_range(mapping, pos, end);
+               ret = -xfs_file_fsync(file, pos, end,
+                                     (file->f_flags & __O_SYNC) ? 0 : 1);
                xfs_rw_ilock(ip, iolock);
-
-               error2 = -xfs_file_fsync(file,
-                                        (file->f_flags & __O_SYNC) ? 0 : 1);
-               if (error)
-                       ret = error;
-               else if (error2)
-                       ret = error2;
        }
 
 out_unlock:

-- 
Markus

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