Re: 回覆: 回覆: [PATCH] f2fs: avoid the deadlock case when stopping discard thread

[Jaegeuk Kim]

On 04/03, Light Hsieh (謝明燈) wrote:
> Our log shows that thaw_super_locked() find that sb is readonly, so sb_freeze_unlock() is not invoked.
> 
> static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
> {
>       ...
>       if (sb_rdonly(sb)) {
>             sb->s_writers.freeze_holders &= ~who;
>             sb->s_writers.frozen = SB_UNFROZEN;
>             wake_up_var(&sb->s_writers.frozen);
>             goto out;
>       }
>                ...
>       sb_freeze_unlock(sb, SB_FREEZE_FS);
> out:
>       deactivate_locked_super(sb);
>       return 0;
> }

Thank you. Could you please take a look at this patch?

https://lore.kernel.org/linux-f2fs-devel/20240404195254.556896-1-jaegeuk@xxxxxxxxxx/T/#u

> 
> 寄件者: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> 寄件日期: 2024年3月27日 上午 12:52
> 收件者: Light Hsieh (謝明燈) <Light.Hsieh@xxxxxxxxxxxx>
> 副本: Hillf Danton <hdanton@xxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx <linux-kernel@xxxxxxxxxxxxxxx>; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx <linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx>
> 主旨: Re: 回覆: [PATCH] f2fs: avoid the deadlock case when stopping discard thread
>  
> 
> External email : Please do not click links or open attachments until you have verified the sender or the content.
> On 03/22, Jaegeuk Kim wrote:
> > On 03/22, Light Hsieh (謝明燈) wrote:
> > > I don't see my added log in sb_free_unlock() which will invoke percpu_up_write to release the write semaphore.
> > 
> > May I ask more details whether thaw_super() was called or not?
> 
> Ping?
> 
> > 
> > > 
> > > 
> > > ________________________________
> > > 寄件者: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > > 寄件日期: 2024年3月22日 上午 08:29
> > > 收件者: Hillf Danton <hdanton@xxxxxxxx>
> > > 副本: linux-kernel@xxxxxxxxxxxxxxx <linux-kernel@xxxxxxxxxxxxxxx>; Light Hsieh (謝明燈) <Light.Hsieh@xxxxxxxxxxxx>; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx <linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx>
> > > 主旨: Re: [PATCH] f2fs: avoid the deadlock case when stopping discard thread
> > > 
> > > 
> > > External email : Please do not click links or open attachments until you have verified the sender or the content.
> > > 
> > > On 03/22, Hillf Danton wrote:
> > > > On Tue, 19 Mar 2024 17:14:42 -0700 Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > > > > f2fs_ioc_shutdown(F2FS_GOING_DOWN_NOSYNC)  issue_discard_thread
> > > > >  - mnt_want_write_file()
> > > > >    - sb_start_write(SB_FREEZE_WRITE)
> > > >  __sb_start_write()
> > > >    percpu_down_read()
> > > > >                                              - sb_start_intwrite(SB_FREEZE_FS);
> > > >    __sb_start_write()
> > > >      percpu_down_read()
> > > >
> > > > Given lock acquirers for read on both sides, wtf deadlock are you fixing?
> > > 
> > > Damn. I couldn't think _write uses _read sem.
> > > 
> > > >
> > > > >  - f2fs_stop_checkpoint(sbi, false,            : waiting
> > > > >     STOP_CP_REASON_SHUTDOWN);
> > > > >  - f2fs_stop_discard_thread(sbi);
> > > > >    - kthread_stop()
> > > > >      : waiting
> > > > >
> > > > >  - mnt_drop_write_file(filp);
> > > >
> > > > More important, feel free to add in spin.
> > > 
> > > I posted this patch before Light reported.
> > > 
> > > And, in the report, I didn't get this:
> > > 
> > > f2fs_ioc_shutdown() --> freeze_bdev() --> freeze_super() --> sb_wait_write(sb, SB_FREEZE_FS) --> ... ->percpu_down_write().
> > > 
> > > because f2fs_ioc_shutdown() calls f2fs_stop_discard_thread() after thaw_bdev()
> > > like this order.
> > > 
> > >  -> freeze_bdev()
> > >  -> thaw_bdev()
> > >  -> f2fs_stop_discard_thread()
> > > 
> > > Am I missing something?
> > > 
> > > >
> > > > Reported-by: "Light Hsieh (謝明燈)" <Light.Hsieh@xxxxxxxxxxxx>
> > >