Patch "GFS2: Take inode off order_write list when setting jdata flag" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

GFS2: Take inode off order_write list when setting jdata flag

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
gfs2-take-inode-off-order_write-list-when-setting-jdata-flag.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Bob Peterson <[email protected]>
Date: Wed, 20 Sep 2017 08:30:04 -0500
Subject: GFS2: Take inode off order_write list when setting jdata flag

From: Bob Peterson <[email protected]>

[ Upstream commit cc555b09d8c3817aeebda43a14ab67049a5653f7 ]

This patch fixes a deadlock caused when the jdata flag is set for inodes that are already on the ordered write list. Since it is on the ordered write list, log_flush calls gfs2_ordered_write which calls filemap_fdatawrite. But since the inode had the jdata flag set, that calls gfs2_jdata_writepages, which tries to start a new transaction. A new transaction cannot be started because it tries to acquire the log_flush rwsem which is already locked by the log flush operation.

The bottom line is: We cannot switch an inode from ordered to jdata until we eliminate any ordered data pages (via log flush) or any log_flush operation afterward will create the circular dependency above. So we need to flush the log before setting the diskflags to switch the file mode, then we need to remove the inode from the ordered writes list.

Before this patch, the log flush was done for jdata->ordered, but that's wrong. If we're going from jdata to ordered, we don't need to call gfs2_log_flush because the call to filemap_fdatawrite will do it for us:

filemap_fdatawrite() -> __filemap_fdatawrite_range()

      __filemap_fdatawrite_range() -> do_writepages()
         do_writepages() -> gfs2_jdata_writepages()
            gfs2_jdata_writepages() -> gfs2_log_flush()

This patch modifies function do_gfs2_set_flags so that if a file has its jdata flag set, and it's already on the ordered write list, the log will be flushed and it will be removed from the list before setting the flag.

---
 fs/gfs2/file.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

@@ -256,7 +256,7 @@ static int do_gfs2_set_flags(struct file
 			goto out;
 	}
 	if ((flags ^ new_flags) & GFS2_DIF_JDATA) {
-		if (flags & GFS2_DIF_JDATA)
+		if (new_flags & GFS2_DIF_JDATA)
 			gfs2_log_flush(sdp, ip->i_gl, NORMAL_FLUSH);
 		error = filemap_fdatawrite(inode->i_mapping);
 		if (error)

@@ -264,6 +264,8 @@ static int do_gfs2_set_flags(struct file
 		error = filemap_fdatawait(inode->i_mapping);
 		if (error)
 			goto out;
+		if (new_flags & GFS2_DIF_JDATA)
+			gfs2_ordered_del_inode(ip);
 	}
 	error = gfs2_trans_begin(sdp, RES_DINODE, 0);
 	if (error)

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/gfs2-take-inode-off-order_write-list-when-setting-jdata-flag.patch