Don't hold lock_super() while running ->sync_fs().

It can deadlock, because:

a) ext3_sync_fs() has to wait until a transaction has finished.

b) a transaction cannot finish when someone else holds lock_super().
    Because lock_super() is used in the block allocator.




 Documentation/filesystems/Locking |    2 ++
 fs/buffer.c                       |    2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

--- linux-2.4.20-ext3merge/Documentation/filesystems/Locking.=K0030=.orig	2002-12-16 17:09:44.000000000 +0000
+++ linux-2.4.20-ext3merge/Documentation/filesystems/Locking	2002-12-16 17:09:44.000000000 +0000
@@ -93,6 +93,7 @@
 	void (*delete_inode) (struct inode *);
 	void (*put_super) (struct super_block *);
 	void (*write_super) (struct super_block *);
+	int (*sync_fs) (struct super_block *);
 	int (*statfs) (struct super_block *, struct statfs *);
 	int (*remount_fs) (struct super_block *, int *, char *);
 	void (*clear_inode) (struct inode *);
@@ -108,6 +109,7 @@
 clear_inode:	no	
 put_super:	yes	yes	maybe		(see below)
 write_super:	yes	yes	maybe		(see below)
+write_super:	yes	no	maybe		(see below)
 statfs:		yes	no	no
 remount_fs:	yes	yes	maybe		(see below)
 umount_begin:	yes	no	maybe		(see below)
--- linux-2.4.20-ext3merge/fs/buffer.c.=K0030=.orig	2002-12-16 17:09:44.000000000 +0000
+++ linux-2.4.20-ext3merge/fs/buffer.c	2002-12-16 17:09:44.000000000 +0000
@@ -328,9 +328,9 @@
 	lock_super(sb);
 	if (sb->s_dirt && sb->s_op && sb->s_op->write_super)
 		sb->s_op->write_super(sb);
+	unlock_super(sb);
 	if (sb->s_op && sb->s_op->sync_fs)
 		sb->s_op->sync_fs(sb);
-	unlock_super(sb);
 	unlock_kernel();
 
 	return sync_buffers(dev, 1);