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Date:   Wed, 19 Jun 2019 10:26:51 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: add a rw_sem to cover quota flag
 changes
Message-ID: <20190619172651.GB57884@jaegeuk-macbookpro.roam.corp.google.com>
References: <20190530033115.16853-1-jaegeuk@kernel.org>
 <20190530175714.GB28719@jaegeuk-macbookpro.roam.corp.google.com>
 <20190604183619.GA8507@jaegeuk-macbookpro.roam.corp.google.com>
 <2afe0416-fe2d-8ba8-7625-0246aca9eba6@huawei.com>
 <20190614024655.GA18113@jaegeuk-macbookpro.roam.corp.google.com>
 <6f70ae56-45eb-666d-ae55-48eb0cc96f32@huawei.com>
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On 06/18, Chao Yu wrote:
> On 2019/6/14 10:46, Jaegeuk Kim wrote:
> > On 06/11, Chao Yu wrote:
> >> On 2019/6/5 2:36, Jaegeuk Kim wrote:
> >>> Two paths to update quota and f2fs_lock_op:
> >>>
> >>> 1.
> >>>  - lock_op
> >>>  |  - quota_update
> >>>  `- unlock_op
> >>>
> >>> 2.
> >>>  - quota_update
> >>>  - lock_op
> >>>  `- unlock_op
> >>>
> >>> But, we need to make a transaction on quota_update + lock_op in #2 case.
> >>> So, this patch introduces:
> >>> 1. lock_op
> >>> 2. down_write
> >>> 3. check __need_flush
> >>> 4. up_write
> >>> 5. if there is dirty quota entries, flush them
> >>> 6. otherwise, good to go
> >>>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> >>> ---
> >>>
> >>> v3 from v2:
> >>>  - refactor to fix quota corruption issue
> >>>   : it seems that the previous scenario is not real and no deadlock case was
> >>>     encountered.
> >>
> >> - f2fs_dquot_commit
> >>  - down_read(&sbi->quota_sem)
> >> 					- block_operation
> >> 					 - f2fs_lock_all
> >> 					  - need_flush_quota
> >> 					   - down_write(&sbi->quota_sem)
> >>   - f2fs_quota_write
> >>    - f2fs_lock_op
> >>
> >> Why can't this happen?
> >>
> >> Once more question, should we hold quota_sem during checkpoint to avoid further
> >> quota update? f2fs_lock_op can do this job as well?
> > 
> > I couldn't find write_dquot() call to make this happen, and f2fs_lock_op was not
> 
> - f2fs_dquot_commit
>  - dquot_commit
>   ->commit_dqblk (v2_write_dquot)
>    - qtree_write_dquot
>     ->quota_write (f2fs_quota_write)
>      - f2fs_lock_op
> 
> Do you mean there is no such way that calling f2fs_lock_op() from
> f2fs_quota_write()? So that deadlock condition is not existing?

I mean write_dquot->f2fs_dquot_commit and block_operation seems not racing
together.

> 
> Thanks,
> 
> > enough to cover quota updates. Current stress & power-cut tests are running for
> > several days without problem with this patch.
> > 
> >>
> >> Thanks,
> >>
> >>>
> >>>  fs/f2fs/checkpoint.c | 41 +++++++++++++++++++----------------------
> >>>  fs/f2fs/f2fs.h       |  1 +
> >>>  fs/f2fs/super.c      | 26 +++++++++++++++++++++-----
> >>>  3 files changed, 41 insertions(+), 27 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >>> index 89825261d474..43f65f0962e5 100644
> >>> --- a/fs/f2fs/checkpoint.c
> >>> +++ b/fs/f2fs/checkpoint.c
> >>> @@ -1131,17 +1131,24 @@ static void __prepare_cp_block(struct f2fs_sb_info *sbi)
> >>>  
> >>>  static bool __need_flush_quota(struct f2fs_sb_info *sbi)
> >>>  {
> >>> +	bool ret = false;
> >>> +
> >>>  	if (!is_journalled_quota(sbi))
> >>>  		return false;
> >>> -	if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH))
> >>> -		return false;
> >>> -	if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR))
> >>> -		return false;
> >>> -	if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_FLUSH))
> >>> -		return true;
> >>> -	if (get_pages(sbi, F2FS_DIRTY_QDATA))
> >>> -		return true;
> >>> -	return false;
> >>> +
> >>> +	down_write(&sbi->quota_sem);
> >>> +	if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH)) {
> >>> +		ret = false;
> >>> +	} else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR)) {
> >>> +		ret = false;
> >>> +	} else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_FLUSH)) {
> >>> +		clear_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
> >>> +		ret = true;
> >>> +	} else if (get_pages(sbi, F2FS_DIRTY_QDATA)) {
> >>> +		ret = true;
> >>> +	}
> >>> +	up_write(&sbi->quota_sem);
> >>> +	return ret;
> >>>  }
> >>>  
> >>>  /*
> >>> @@ -1160,26 +1167,22 @@ static int block_operations(struct f2fs_sb_info *sbi)
> >>>  	blk_start_plug(&plug);
> >>>  
> >>>  retry_flush_quotas:
> >>> +	f2fs_lock_all(sbi);
> >>>  	if (__need_flush_quota(sbi)) {
> >>>  		int locked;
> >>>  
> >>>  		if (++cnt > DEFAULT_RETRY_QUOTA_FLUSH_COUNT) {
> >>>  			set_sbi_flag(sbi, SBI_QUOTA_SKIP_FLUSH);
> >>> -			f2fs_lock_all(sbi);
> >>> +			set_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
> >>>  			goto retry_flush_dents;
> >>>  		}
> >>> -		clear_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
> >>> +		f2fs_unlock_all(sbi);
> >>>  
> >>>  		/* only failed during mount/umount/freeze/quotactl */
> >>>  		locked = down_read_trylock(&sbi->sb->s_umount);
> >>>  		f2fs_quota_sync(sbi->sb, -1);
> >>>  		if (locked)
> >>>  			up_read(&sbi->sb->s_umount);
> >>> -	}
> >>> -
> >>> -	f2fs_lock_all(sbi);
> >>> -	if (__need_flush_quota(sbi)) {
> >>> -		f2fs_unlock_all(sbi);
> >>>  		cond_resched();
> >>>  		goto retry_flush_quotas;
> >>>  	}
> >>> @@ -1201,12 +1204,6 @@ static int block_operations(struct f2fs_sb_info *sbi)
> >>>  	 */
> >>>  	down_write(&sbi->node_change);
> >>>  
> >>> -	if (__need_flush_quota(sbi)) {
> >>> -		up_write(&sbi->node_change);
> >>> -		f2fs_unlock_all(sbi);
> >>> -		goto retry_flush_quotas;
> >>> -	}
> >>> -
> >>>  	if (get_pages(sbi, F2FS_DIRTY_IMETA)) {
> >>>  		up_write(&sbi->node_change);
> >>>  		f2fs_unlock_all(sbi);
> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>> index 9674a85154b2..9bd2bf0f559b 100644
> >>> --- a/fs/f2fs/f2fs.h
> >>> +++ b/fs/f2fs/f2fs.h
> >>> @@ -1253,6 +1253,7 @@ struct f2fs_sb_info {
> >>>  	block_t unusable_block_count;		/* # of blocks saved by last cp */
> >>>  
> >>>  	unsigned int nquota_files;		/* # of quota sysfile */
> >>> +	struct rw_semaphore quota_sem;		/* blocking cp for flags */
> >>>  
> >>>  	/* # of pages, see count_type */
> >>>  	atomic_t nr_pages[NR_COUNT_TYPE];
> >>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> >>> index 15d7e30bfc72..5a318399a2fa 100644
> >>> --- a/fs/f2fs/super.c
> >>> +++ b/fs/f2fs/super.c
> >>> @@ -1964,6 +1964,7 @@ int f2fs_quota_sync(struct super_block *sb, int type)
> >>>  	int cnt;
> >>>  	int ret;
> >>>  
> >>> +	down_read(&sbi->quota_sem);
> >>>  	ret = dquot_writeback_dquots(sb, type);
> >>>  	if (ret)
> >>>  		goto out;
> >>> @@ -2001,6 +2002,7 @@ int f2fs_quota_sync(struct super_block *sb, int type)
> >>>  out:
> >>>  	if (ret)
> >>>  		set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
> >>> +	up_read(&sbi->quota_sem);
> >>>  	return ret;
> >>>  }
> >>>  
> >>> @@ -2094,32 +2096,40 @@ static void f2fs_truncate_quota_inode_pages(struct super_block *sb)
> >>>  
> >>>  static int f2fs_dquot_commit(struct dquot *dquot)
> >>>  {
> >>> +	struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
> >>>  	int ret;
> >>>  
> >>> +	down_read(&sbi->quota_sem);
> >>>  	ret = dquot_commit(dquot);
> >>>  	if (ret < 0)
> >>> -		set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
> >>> +		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> >>> +	up_read(&sbi->quota_sem);
> >>>  	return ret;
> >>>  }
> >>>  
> >>>  static int f2fs_dquot_acquire(struct dquot *dquot)
> >>>  {
> >>> +	struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
> >>>  	int ret;
> >>>  
> >>> +	down_read(&sbi->quota_sem);
> >>>  	ret = dquot_acquire(dquot);
> >>>  	if (ret < 0)
> >>> -		set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
> >>> -
> >>> +		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> >>> +	up_read(&sbi->quota_sem);
> >>>  	return ret;
> >>>  }
> >>>  
> >>>  static int f2fs_dquot_release(struct dquot *dquot)
> >>>  {
> >>> +	struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
> >>>  	int ret;
> >>>  
> >>> +	down_read(&sbi->quota_sem);
> >>>  	ret = dquot_release(dquot);
> >>>  	if (ret < 0)
> >>> -		set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
> >>> +		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> >>> +	up_read(&sbi->quota_sem);
> >>>  	return ret;
> >>>  }
> >>>  
> >>> @@ -2129,22 +2139,27 @@ static int f2fs_dquot_mark_dquot_dirty(struct dquot *dquot)
> >>>  	struct f2fs_sb_info *sbi = F2FS_SB(sb);
> >>>  	int ret;
> >>>  
> >>> +	down_read(&sbi->quota_sem);
> >>>  	ret = dquot_mark_dquot_dirty(dquot);
> >>>  
> >>>  	/* if we are using journalled quota */
> >>>  	if (is_journalled_quota(sbi))
> >>>  		set_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
> >>>  
> >>> +	up_read(&sbi->quota_sem);
> >>>  	return ret;
> >>>  }
> >>>  
> >>>  static int f2fs_dquot_commit_info(struct super_block *sb, int type)
> >>>  {
> >>> +	struct f2fs_sb_info *sbi = F2FS_SB(sb);
> >>>  	int ret;
> >>>  
> >>> +	down_read(&sbi->quota_sem);
> >>>  	ret = dquot_commit_info(sb, type);
> >>>  	if (ret < 0)
> >>> -		set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
> >>> +		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> >>> +	up_read(&sbi->quota_sem);
> >>>  	return ret;
> >>>  }
> >>>  
> >>> @@ -3253,6 +3268,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> >>>  	}
> >>>  
> >>>  	init_rwsem(&sbi->cp_rwsem);
> >>> +	init_rwsem(&sbi->quota_sem);
> >>>  	init_waitqueue_head(&sbi->cp_wait);
> >>>  	init_sb_info(sbi);
> >>>  
> >>>
> > .
> >