[PATCH v2 1/5] writeback: Fix missed lazytime flush

[Jan Kara <jack@suse.cz>]

move_expired_inodes() moves to b_io list inodes which were dirtied at
current_time - dirtytime_expire_interval or before.
__writeback_single_inode() however calls sync_lazytime() only if the
inode was dirtied strictly before current_time -
dirtytime_expire_interval. It can thus happen that inode with dirty
timestamps gets queued to b_io list, then fails the check in
__writeback_single_inode() and as a result is just placed back to
b_dirty_time list with a refreshed timestamp and so timestamps aren't
written when they should have been.

This is a very difficult race to hit in practice but changes to how
dirty time expiry is handled on last iput() will make this much easier
to hit.

Fixes: 5fcd57505c00 ("writeback: Drop I_DIRTY_TIME_EXPIRE")
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/fs-writeback.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e744f9f9d43f..bb4546d147dc 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1807,8 +1807,8 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	 */
 	if ((inode_state_read_once(inode) & I_DIRTY_TIME) &&
 	    (wbc->sync_mode == WB_SYNC_ALL ||
-	     time_after(jiffies, inode->dirtied_time_when +
-			dirtytime_expire_interval * HZ)))
+	     time_after_eq(jiffies, inode->dirtied_time_when +
+			   dirtytime_expire_interval * HZ)))
 		sync_lazytime(inode);
 
 	/*
-- 
2.51.0