linux-kernel - Re: [f2fs-dev] [PATCH 1/2] f2fs: fix to add missing sb_{start, end}

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Date: Mon, 10 Jun 2024 08:10:41 -0700
From: Daeho Jeong <daeho43@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: jaegeuk@...nel.org, Daeho Jeong <daehojeong@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: fix to add missing sb_{start,
 end}_intwrite() for ckpt thread

On Sat, Jun 8, 2024 at 5:36 AM Chao Yu <chao@...nel.org> wrote:
>
> On 2024/6/6 17:52, Chao Yu wrote:
> > After commit 261eeb9c1585 ("f2fs: introduce checkpoint_merge mount
> > option"), checkpoint can be triggered in background thread, it missed
> > to cover f2fs inner checkpoint operation w/ sb_{start,end}_intwrite(),
> > fix it.
>
> It needs to use sb_start_intwrite_trylock(), otherwise, it will cause
> deadlock as below:
>
> - freeze_super
>   - sb_wait_write(SB_FREEZE_WRITE)
>   - sb_wait_write(SB_FREEZE_PAGEFAULT)
>   - sb_wait_write(SB_FREEZE_FS)
>                                         - sync
>                                          - iterate_supers
>                                           - super_lock_shared
>                                            - down_read(&sb->s_umount)
>                                            - sync_fs_one_sb
>                                             - f2fs_sync_fs
>                                              - f2fs_issue_checkpoint
>                                               - wait_for_completion
>                                                                         - issue_checkpoint_thread
>                                                                          - sb_start_intwrite(sbi->sb);
>
> - thaw_super
>   - super_lock_excl
>    - down_write(&sb->s_umount)
>
> Thanks,
>
> >
> > Fixes: 261eeb9c1585 ("f2fs: introduce checkpoint_merge mount option")
> > Cc: Daeho Jeong <daehojeong@...gle.com>
> > Signed-off-by: Chao Yu <chao@...nel.org>
> > ---
> >   fs/f2fs/checkpoint.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index 55d444bec5c0..66eaad591b60 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -1828,8 +1828,11 @@ static int issue_checkpoint_thread(void *data)
> >       if (kthread_should_stop())
> >               return 0;
> >
> > -     if (!llist_empty(&cprc->issue_list))
> > +     if (!llist_empty(&cprc->issue_list)) {
> > +             sb_start_intwrite(sbi->sb);
> >               __checkpoint_and_complete_reqs(sbi);
> > +             sb_end_intwrite(sbi->sb);
> > +     }
> >
> >       wait_event_interruptible(*q,
> >               kthread_should_stop() || !llist_empty(&cprc->issue_list));
>
>

Reviewed-by: Daeho Jeong <daehojeong@...gle.com>

Thanks.



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