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Date:   Thu, 13 Jun 2019 19:46:55 -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: <20190614024655.GA18113@jaegeuk-macbookpro.roam.corp.google.com>
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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
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);
> >  
> >