Message-ID: <20200716011047.GA2540332@google.com>
Date:   Wed, 15 Jul 2020 18:10:47 -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
Subject: Re: [f2fs-dev] [PATCH] f2fs: don't skip writeback of quota data

On 07/16, Chao Yu wrote:
> On 2020/7/16 3:10, Jaegeuk Kim wrote:
> > On 07/14, Chao Yu wrote:
> >> On 2020/7/14 1:59, Jaegeuk Kim wrote:
> >>> On 07/10, Chao Yu wrote:
> >>>> On 2020/7/10 11:50, Jaegeuk Kim wrote:
> >>>>> On 07/10, Chao Yu wrote:
> >>>>>> On 2020/7/10 11:26, Jaegeuk Kim wrote:
> >>>>>>> On 07/10, Chao Yu wrote:
> >>>>>>>> On 2020/7/10 3:05, Jaegeuk Kim wrote:
> >>>>>>>>> On 07/09, Chao Yu wrote:
> >>>>>>>>>> On 2020/7/9 13:30, Jaegeuk Kim wrote:
> >>>>>>>>>>> It doesn't need to bypass flushing quota data in background.
> >>>>>>>>>>
> >>>>>>>>>> The condition is used to flush quota data in batch to avoid random
> >>>>>>>>>> small-sized udpate, did you hit any problem here?
> >>>>>>>>>
> >>>>>>>>> I suspect this causes fault injection test being stuck by waiting for inode
> >>>>>>>>> writeback completion. With this patch, it has been running w/o any issue so far.
> >>>>>>>>> I keep an eye on this.
> >>>>>>>>
> >>>>>>>> Hmmm.. so that this patch may not fix the root cause, and it may hiding the
> >>>>>>>> issue deeper.
> >>>>>>>>
> >>>>>>>> How about just keeping this patch in our private branch to let fault injection
> >>>>>>>> test not be stuck? until we find the root cause in upstream codes.
> >>>>>>>
> >>>>>>> Well, I don't think this hides something. When the issue happens, I saw inodes
> >>>>>>> being stuck due to writeback while only quota has some dirty data. At that time,
> >>>>>>> there was no dirty data page from other inodes.
> >>>>>>
> >>>>>> Okay,
> >>>>>>
> >>>>>>>
> >>>>>>> More specifically, I suspect __writeback_inodes_sb_nr() gives WB_SYNC_NONE and
> >>>>>>> waits for wb_wait_for_completion().
> >>>>>>
> >>>>>> Did you record any callstack after the issue happened?
> >>>>>
> >>>>> I found this.
> >>>>>
> >>>>> [213389.297642]  __schedule+0x2dd/0x780^M
> >>>>> [213389.299224]  schedule+0x55/0xc0^M
> >>>>> [213389.300745]  wb_wait_for_completion+0x56/0x90^M
> >>>>> [213389.302469]  ? wait_woken+0x80/0x80^M
> >>>>> [213389.303997]  __writeback_inodes_sb_nr+0xa8/0xd0^M
> >>>>> [213389.305760]  writeback_inodes_sb+0x4b/0x60^M
> >>>>> [213389.307439]  sync_filesystem+0x2e/0xa0^M
> >>>>> [213389.308999]  generic_shutdown_super+0x27/0x110^M
> >>>>> [213389.310738]  kill_block_super+0x27/0x50^M
> >>>>> [213389.312327]  kill_f2fs_super+0x76/0xe0 [f2fs]^M
> >>>>> [213389.314014]  deactivate_locked_super+0x3b/0x80^M
> >>>>> [213389.315692]  deactivate_super+0x3e/0x50^M
> >>>>> [213389.317226]  cleanup_mnt+0x109/0x160^M
> >>>>> [213389.318718]  __cleanup_mnt+0x12/0x20^M
> >>>>> [213389.320177]  task_work_run+0x70/0xb0^M
> >>>>> [213389.321609]  exit_to_usermode_loop+0x131/0x160^M
> >>>>> [213389.323306]  do_syscall_64+0x170/0x1b0^M
> >>>>> [213389.324762]  entry_SYSCALL_64_after_hwframe+0x44/0xa9^M
> >>>>> [213389.326477] RIP: 0033:0x7fc4b5e6a35b^M
> >>>>
> >>>> Does this only happen during umount? If so, will below change help?
> >>>>
> >>>> 	if ((S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode)) &&
> >>>> +			!is_sbi_flag_set(sbi, SBI_IS_CLOSE) &&
> >>>> 			wbc->sync_mode == WB_SYNC_NONE &&
> >>>> 			get_dirty_pages(inode) < nr_pages_to_skip(sbi, DATA) &&
> >>>> 			f2fs_available_free_memory(sbi, DIRTY_DENTS))
> >>>> 		goto skip_write;
> >>>
> >>> Hmm, this doesn't work. The writeback was called before put_super?
> >>
> >> Oops, still be confused about this issue. :(
> > 
> > Huam, I hit the problem with the patch.
> > I need to return back and think in other way. :(
> 
> Still quota data was left? what about dentry?

Huh, at this time, only node and meta pages were left as dirty.

> 
> Thanks,
> 
> > 
> >>
> >> Thanks,
> >>
> >>> I'll try the original patch one more time.
> >>>
> >>>>
> >>>>>
> >>>>>>
> >>>>>> Still I'm confused that why directory's data written could be skipped, but
> >>>>>> quota's data couldn't, what's the difference?
> >>>>>
> >>>>> I suspect different blocking timing from cp_error between quota and dentry.
> >>>>> e.g., we block dir operations right after cp_error, while quota can make
> >>>>
> >>>> No guarantee that there is no dirty dentry being created after
> >>>> cp_error, right?
> >>>>
> >>>> e.g.
> >>>>
> >>>> Thread A				Thread B
> >>>> - f2fs_create
> >>>> - bypass f2fs_cp_error
> >>>> 					- set cp_error
> >>>> - create dirty dentry
> >>>>
> >>>> BTW, do you know what __writeback_inodes_sb_nr is waiting for?
> >>>>
> >>>>> dirty pages in more fine granularity.
> >>>>>
> >>>>>>
> >>>>>>>
> >>>>>>>>
> >>>>>>>> Thanks,
> >>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Thanks,
> >>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> Thanks,
> >>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> >>>>>>>>>>> ---
> >>>>>>>>>>>  fs/f2fs/data.c | 2 +-
> >>>>>>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>>>>>>>
> >>>>>>>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >>>>>>>>>>> index 44645f4f914b6..72e8b50e588c1 100644
> >>>>>>>>>>> --- a/fs/f2fs/data.c
> >>>>>>>>>>> +++ b/fs/f2fs/data.c
> >>>>>>>>>>> @@ -3148,7 +3148,7 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
> >>>>>>>>>>>  	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
> >>>>>>>>>>>  		goto skip_write;
> >>>>>>>>>>>  
> >>>>>>>>>>> -	if ((S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode)) &&
> >>>>>>>>>>> +	if (S_ISDIR(inode->i_mode) &&
> >>>>>>>>>>>  			wbc->sync_mode == WB_SYNC_NONE &&
> >>>>>>>>>>>  			get_dirty_pages(inode) < nr_pages_to_skip(sbi, DATA) &&
> >>>>>>>>>>>  			f2fs_available_free_memory(sbi, DIRTY_DENTS))
> >>>>>>>>>>>
> >>>>>>>>> .
> >>>>>>>>>
> >>>>>>> .
> >>>>>>>
> >>>>> .
> >>>>>
> >>> .
> >>>
> > .
> > 

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