linux-kernel - Re: [PATCH] writeback: Avoid skipping inode writeback

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Date:   Mon, 9 May 2022 17:37:45 +0800
From:   jing xia <jing.xia.mail@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Jing Xia <jing.xia@...soc.com>, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] writeback: Avoid skipping inode writeback

Thanks, I'll update the patch.

On Thu, May 5, 2022 at 11:40 PM Jan Kara <jack@...e.cz> wrote:
>
> On Thu 05-05-22 21:47:31, 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.
> >
> > Signed-off-by: Jing Xia <jing.xia@...soc.com>
>
> Thanks for report and the fix! The patch looks good so feel free to add:
>
> Reviewed-by: Jan Kara <jack@...e.cz>
>
> Also please add tags:
>
> CC: stable@...r.kernel.org
> Fixes: 0ae45f63d4ef ("vfs: add support for a lazytime mount option")
>
> Thanks.
>                                                                 Honza
>
> > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > index 591fe9cf1659..d7763feaf14a 100644
> > --- a/fs/fs-writeback.c
> > +++ b/fs/fs-writeback.c
> > @@ -1712,6 +1712,9 @@ 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@...e.com>
> SUSE Labs, CR