[PATCH] block new writers on frozen filesystems

When the lockfs patches went in an important bit got lost, the call in
generic_file_write to put newly incoming writers to sleep when a filesystem
is frozen.  Nathan added back the call in the now separate XFS write patch,
and the patch for the generic code is below:
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/filemap.c

@@ -2078,6 +2078,8 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
 	count = ocount;
 	pos = *ppos;
 
+	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
+
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = mapping->backing_dev_info;
 	written = 0;