writeback: reset dirtied_when when switching wbs

When switching a dirty inode to another wb, inode_do_switch_wbs() puts
it at the newest end of the target b_dirty list instead of searching
for its sorted position. This requires updating dirtied_when, which
move_expired_inodes() uses to decide where to stop scanning.

However, the switch updates dirtied_time_when instead. This leaves
b_dirty out of order and can make the scan stop before reaching older
inodes. It also resets the lazytime expiration timestamp, potentially
delaying timestamp writeback.

Update dirtied_when instead, preserving both the constant-time insertion
and the lazytime expiration timestamp. Correct the field name in the
comment and document the distinction between the two inode timestamps.

Fixes: 9a6ebbdbd412 ("writeback: Avoid excessively long inode switching times")
Cc: stable@vger.kernel.org
Signed-off-by: Julian Sun <sunjunchao@bytedance.com>
Link: https://patch.msgid.link/20261016115230.3640770-2-sunjunchao@bytedance.com
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions