[Cluster-devel] [GFS2 PATCH] gfs2: Remove sb_start_write from gfs2_statfs_sync

[Bob Peterson <rpeterso@redhat.com>]

Hi,

Before this patch, function gfs2_statfs_sync called sb_start_write. This is a
violation of the basic vfs rules that state that sb_start_write should always
be taken before s_umount. See this document:

https://www.kernel.org/doc/htmldocs/filesystems/API-sb-start-write.html

"Since freeze protection behaves as a lock, users have to preserve
ordering of freeze protection and other filesystem locks. Generally,
freeze protection should be the outermost lock. In particular, we have:

sb_start_write -> i_mutex (write path, truncate, directory ops, ...) ->
s_umount (freeze_super, thaw_super)"

deactivate_super
   down_write(&s->s_umount); <------------------------------------ s_umount
   deactivate_locked_super
      gfs2_kill_sb
         kill_block_super
            generic_shutdown_super
               gfs2_put_super
                  gfs2_make_fs_ro
                     gfs2_statfs_sync(sdp->sd_vfs, 0);
                        sb_start_write <--------------------- sb_start_write

As far as I can tell, gfs2_statfs_sync doesn't need to call sb_start_write
any more than any other write to the file system, which are policed by glocks.
None of the other functions in gfs2 lock sb_start_write so it only affects
how vfs calls gfs2.

This patch simply removes the call to sb_start_write.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
---
 fs/gfs2/super.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index b3d951ab8068..2f56acc41c04 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -353,7 +353,6 @@ int gfs2_statfs_sync(struct super_block *sb, int type)
 	struct buffer_head *m_bh, *l_bh;
 	int error;
 
-	sb_start_write(sb);
 	error = gfs2_glock_nq_init(m_ip->i_gl, LM_ST_EXCLUSIVE, GL_NOCACHE,
 				   &gh);
 	if (error)
@@ -392,7 +391,6 @@ int gfs2_statfs_sync(struct super_block *sb, int type)
 out_unlock:
 	gfs2_glock_dq_uninit(&gh);
 out:
-	sb_end_write(sb);
 	return error;
 }