[PATCH V2] writeback: Avoid skipping inode writeback

[PATCH V2] writeback: Avoid skipping inode writeback

[Jing Xia]

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>
---
 fs/fs-writeback.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 591fe9cf1659..1fae0196292a 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1712,6 +1712,10 @@ static int writeback_single_inode(struct inode *inode,
 	 */
 	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);
 out:
-- 
2.17.1

Re: [PATCH V2] writeback: Avoid skipping inode writeback

[Jan Kara]

On Tue 10-05-22 10:35:14, Jing Xia wrote:
> 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>

Thanks. I've queued the patch to my tree and will push it to Linus tomorrow
or so.

								Honza

> ---
>  fs/fs-writeback.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 591fe9cf1659..1fae0196292a 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -1712,6 +1712,10 @@ static int writeback_single_inode(struct inode *inode,
>  	 */
>  	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);
>  out:
> -- 
> 2.17.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR