linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: don't set RO when shutting down f2fs

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Date: Tue, 9 Apr 2024 16:21:58 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
	Light Hsieh (謝明燈) <Light.Hsieh@...iatek.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: don't set RO when shutting down f2fs

On 04/09, Chao Yu wrote:
> On 2024/4/5 3:52, Jaegeuk Kim wrote:
> > Shutdown does not check the error of thaw_super due to readonly, which
> > causes a deadlock like below.
> > 
> > f2fs_ioc_shutdown(F2FS_GOING_DOWN_FULLSYNC)        issue_discard_thread
> >   - bdev_freeze
> >    - freeze_super
> >   - f2fs_stop_checkpoint()
> >    - f2fs_handle_critical_error                     - sb_start_write
> >      - set RO                                         - waiting
> >   - bdev_thaw
> >    - thaw_super_locked
> >      - return -EINVAL, if sb_rdonly()
> >   - f2fs_stop_discard_thread
> >    -> wait for kthread_stop(discard_thread);
> > 
> > Reported-by: "Light Hsieh (謝明燈)" <Light.Hsieh@...iatek.com>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> >   fs/f2fs/super.c | 11 +++++++++--
> >   1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index df9765b41dac..ba6288e870c5 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -4135,9 +4135,16 @@ void f2fs_handle_critical_error(struct f2fs_sb_info *sbi, unsigned char reason,
> >   	if (shutdown)
> >   		set_sbi_flag(sbi, SBI_IS_SHUTDOWN);
> > -	/* continue filesystem operators if errors=continue */
> > -	if (continue_fs || f2fs_readonly(sb))
> > +	/*
> > +	 * Continue filesystem operators if errors=continue. Should not set
> > +	 * RO by shutdown, since RO bypasses thaw_super which can hang the
> > +	 * system.
> > +	 */
> > +	if (continue_fs || f2fs_readonly(sb) ||
> > +				reason == STOP_CP_REASON_SHUTDOWN) {
> > +		f2fs_warn(sbi, "Stopped filesystem due to readon: %d", reason);
> >   		return;
> 
> Do we need to set RO after bdev_thaw() in f2fs_do_shutdown()?

IIRC, shutdown doesn't need to set RO as we stopped the checkpoint.
I'm more concerned on any side effect caused by this RO change.

> 
> Thanks,
> 
> > +	}
> >   	f2fs_warn(sbi, "Remounting filesystem read-only");
> >   	/*