Re: [f2fs-dev] [PATCH] f2fs: add a rw_sem to cover quota flag changes

[Chao Yu <chao@kernel.org>]

On 2019-5-30 11:31, Jaegeuk Kim wrote:
> thread 1:                        thread 2:
> writeback                        checkpoint
> set QUOTA_NEED_FLUSH
>                                  clear QUOTA_NEED_FLUSH
> f2fs_dquot_commit
> dquot_commit
> clear_dquot_dirty
>                                  f2fs_quota_sync
>                                  dquot_writeback_dquots
> 				 nothing to commit
> commit_dqblk
> quota_write
> f2fs_quota_write
> waiting for f2fs_lock_op()
> 				 pass __need_flush_quota
>                                  (no F2FS_DIRTY_QDATA)

At a glance, will it cause deadlock:

- 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

Thanks,

> 
> -> up-to-date quota is not written
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>  fs/f2fs/checkpoint.c | 26 ++++++++++++++++----------
>  fs/f2fs/f2fs.h       |  1 +
>  fs/f2fs/super.c      | 27 ++++++++++++++++++++++-----
>  3 files changed, 39 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 89825261d474..cf3b15c963d2 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1131,17 +1131,23 @@ static void __prepare_cp_block(struct f2fs_sb_info *sbi)
>  
>  static bool __need_flush_quota(struct f2fs_sb_info *sbi)
>  {
> +	bool ret = false;
> +
> +	down_write(&sbi->quota_sem);
>  	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;
> +		ret = false;
> +	else 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))
> +		ret = true;
> +	else if (get_pages(sbi, F2FS_DIRTY_QDATA))
> +		ret = true;
> +	else
> +		ret = false;
> +	up_write(&sbi->quota_sem);
> +	return ret;
>  }
>  
>  /*
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 9b3d9977cd1e..692c0922f5b2 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1250,6 +1250,7 @@ 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 912e2619d581..5ddf5e97ee60 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1944,7 +1944,10 @@ 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);
> +	up_read(&sbi->quota_sem);
> +
>  	if (ret)
>  		goto out;
>  
> @@ -2074,32 +2077,40 @@ 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;
>  }
>  
> @@ -2109,22 +2120,27 @@ 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;
>  }
>  
> @@ -3233,6 +3249,7 @@ 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);
>  
>