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Subject: Re: [f2fs-dev] [PATCH v3] f2fs: add a rw_sem to cover quota flag
 changes
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
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>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <6f70ae56-45eb-666d-ae55-48eb0cc96f32@huawei.com>
Date:   Tue, 18 Jun 2019 14:52:52 +0800
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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?

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);
>>>  
>>>
> .
>