[PATCH] [Unstable] ext4: properly check for dirty state in ext4_inode_datasync_dirty()

[Andrea Righi]

ext4_inode_datasync_dirty() needs to return 'true' if the inode is
dirty, 'false' otherwise, but the logic seems to be incorrectly changed
by commit aa75f4d3daae ("ext4: main fast-commit commit path").

This introduces a problem with swap files that are always failing to be
activated, showing this error in dmesg:

 [   34.406479] swapon: file is not committed

Simple test case to reproduce the problem:

  # fallocate -l 8G swapfile
  # chmod 0600 swapfile
  # mkswap swapfile
  # swapon swapfile

Fix the logic to return the proper state of the inode.

Link: https://lore.kernel.org/lkml/20201024131333.GA32124@xps-13-7390
Fixes: aa75f4d3daae ("ext4: main fast-commit commit path")
Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
Signed-off-by: Harshad Shirwadkar <harshadshirwadkar at gmail.com>
(cherry picked from commit a316082fa331d086dd8dea9d1e10c7fac3cbbad6 https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git)
Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
---
 fs/ext4/inode.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 03c2253005f0..520a0209451e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3307,10 +3307,12 @@ static bool ext4_inode_datasync_dirty(struct inode *inode)
 
 	if (journal) {
 		if (jbd2_transaction_committed(journal,
-					EXT4_I(inode)->i_datasync_tid))
-			return true;
-		return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) >=
-			EXT4_I(inode)->i_fc_committed_subtid;
+			EXT4_I(inode)->i_datasync_tid))
+			return false;
+		if (test_opt2(inode->i_sb, JOURNAL_FAST_COMMIT))
+			return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) <
+				EXT4_I(inode)->i_fc_committed_subtid;
+		return true;
 	}
 
 	/* Any metadata buffers to write? */
-- 
2.27.0