[PATCH 5.15 089/102] writeback: Avoid skipping inode writeback

Greg Kroah-Hartman
2022-05-16T20:19:18Z

From: Jing Xia <jing.xia@unisoc.com>

commit 846a3351ddfe4a86eede4bb26a205c3f38ef84d3 upstream.

We have run into an issue that a task gets stuck in
balance_dirty_pages_ratelimited() when perform I/O stress testing.
The reason we observed is that an I_DIRTY_PAGES inode with lots
of dirty pages is in b_dirty_time list and standard background
writeback cannot writeback the inode.
After studing the relevant code, the following scenario may lead
to the issue:

task1 task2
----- -----
fuse_flush
write_inode_now //in b_dirty_time
writeback_single_inode
__writeback_single_inode
fuse_write_end
filemap_dirty_folio
__xa_set_mark:PAGECACHE_TAG_DIRTY
lock inode->i_lock
if mapping tagged PAGECACHE_TAG_DIRTY
inode->i_state |= I_DIRTY_PAGES
unlock inode->i_lock
__mark_inode_dirty:I_DIRTY_PAGES
lock inode->i_lock
-was dirty,inode stays in
-b_dirty_time
unlock inode->i_lock

if(!(inode->i_state & I_DIRTY_All))
-not true,so nothing done

This patch moves the dirty inode to b_dirty list when the inode
currently is not queued in b_io or b_more_io list at the end of
writeback_single_inode.

Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
CC: stable@vger.kernel.org
Fixes: 0ae45f63d4ef ("vfs: add support for a lazytime mount option")
Signed-off-by: Jing Xia <jing.xia@unisoc.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220510023514.27399-1-jing.xia@unisoc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/fs-writeback.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1739,6 +1739,10 @@ static int writeback_single_inode(struct
*/
if (!(inode->i_state & I_DIRTY_ALL))
inode_cgwb_move_to_attached(inode, wb);
+ else if (!(inode->i_state & I_SYNC_QUEUED) &&
+ (inode->i_state & I_DIRTY))
+ redirty_tail_locked(inode, wb);
+
spin_unlock(&wb->list_lock);
inode_sync_complete(inode);