linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix deadlock between quota writes and checkpoint

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Message-ID: <20200804035439.GA903802@google.com>
Date:   Mon, 3 Aug 2020 20:54:39 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix deadlock between quota writes and
 checkpoint

On 08/04, Chao Yu wrote:
> On 2020/7/29 15:02, Jaegeuk Kim wrote:
> > f2fs_write_data_pages(quota_mapping)
> >   __f2fs_write_data_pages             f2fs_write_checkpoint
> >    * blk_start_plug(&plug);
> >    * add bio in write_io[DATA]
> >                                        - block_operations
> >                                        - skip syncing quota by
> >                                                  >DEFAULT_RETRY_QUOTA_FLUSH_COUNT
> >                                        - down_write(&sbi->node_write);
> 
> f2fs_flush_merged_writes() will be called after block_operations(), why this doesn't
> help?

Well, I think bio can be added after f2fs_flush_merged_writes() as well.

> 
> >    - f2fs_write_single_data_page
> >      - f2fs_do_write_data_page
> >        - f2fs_outplace_write_data
> >          - do_write_page
> >             - f2fs_allocate_data_block
> >              - down_write(node_write)
> >                                        - f2fs_wait_on_all_pages(F2FS_WB_CP_DATA);
> > 
> > Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> >   fs/f2fs/checkpoint.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index 8c782d3f324f0..99c8061da55b9 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -1269,6 +1269,8 @@ void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type)
> >   		if (type == F2FS_DIRTY_META)
> >   			f2fs_sync_meta_pages(sbi, META, LONG_MAX,
> >   							FS_CP_META_IO);
> > +		else if (type == F2FS_WB_CP_DATA)
> > +			f2fs_submit_merged_write(sbi, DATA);
> >   		io_schedule_timeout(DEFAULT_IO_TIMEOUT);
> >   	}
> >   	finish_wait(&sbi->cp_wait, &wait);
> >