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Date:   Thu, 3 Sep 2020 10:48:04 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Daeho Jeong <daeho43@gmail.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: change i_compr_blocks of inode to
 atomic value
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References: <20200903030320.330507-1-daeho43@gmail.com>
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On 09/03, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@google.com>
> 
> writepages() can be concurrently invoked for the same file by different
> threads such as a thread fsyncing the file and a kworker kernel thread.
> So, changing i_compr_blocks without protection is racy and we need to
> protect it by changing it with atomic type value. Plus, we don't need
> a 64bit value for i_compr_blocks, so just we will use a atomic value,
> not atomic64.
> 
> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> ---
> Changes in v2:
>  - Change atomic64 to atomic and remove unnecessary part
> ---
>  fs/f2fs/f2fs.h  | 18 ++++++++----------
>  fs/f2fs/file.c  | 22 ++++++++++++----------
>  fs/f2fs/inode.c | 11 +++++++----
>  fs/f2fs/super.c |  1 +
>  4 files changed, 28 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index f60414805e05..f6b8ac10a55c 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -801,7 +801,7 @@ struct f2fs_inode_info {
>  	struct timespec64 i_disk_time[4];/* inode disk times */
>  
>  	/* for file compress */
> -	u64 i_compr_blocks;			/* # of compressed blocks */
> +	atomic_t i_compr_blocks;		/* # of compressed blocks */
>  	unsigned char i_compress_algorithm;	/* algorithm type */
>  	unsigned char i_log_cluster_size;	/* log of cluster size */
>  	unsigned int i_cluster_size;		/* cluster size */
> @@ -3936,12 +3936,9 @@ static inline u64 f2fs_disable_compressed_file(struct inode *inode)
>  
>  	if (!f2fs_compressed_file(inode))
>  		return 0;
> -	if (S_ISREG(inode->i_mode)) {
> -		if (get_dirty_pages(inode))
> -			return 1;
> -		if (fi->i_compr_blocks)
> -			return fi->i_compr_blocks;
> -	}
> +	if (S_ISREG(inode->i_mode) &&
> +		(get_dirty_pages(inode) || atomic_read(&fi->i_compr_blocks)))
> +		return 1;

Please keep the original flow in this patch which says swithing to atomic.
Instead, it'd be better to have another patch which cleans up
f2fs_disable_compressed_file() having "bool" as a return value.

>  
>  	fi->i_flags &= ~F2FS_COMPR_FL;
>  	stat_dec_compr_inode(inode);
> @@ -4057,16 +4054,17 @@ static inline void f2fs_i_compr_blocks_update(struct inode *inode,
>  						u64 blocks, bool add)
>  {
>  	int diff = F2FS_I(inode)->i_cluster_size - blocks;
> +	struct f2fs_inode_info *fi = F2FS_I(inode);
>  
>  	/* don't update i_compr_blocks if saved blocks were released */
> -	if (!add && !F2FS_I(inode)->i_compr_blocks)
> +	if (!add && !atomic_read(&fi->i_compr_blocks))
>  		return;
>  
>  	if (add) {
> -		F2FS_I(inode)->i_compr_blocks += diff;
> +		atomic_add(diff, &fi->i_compr_blocks);
>  		stat_add_compr_blocks(inode, diff);
>  	} else {
> -		F2FS_I(inode)->i_compr_blocks -= diff;
> +		atomic_sub(diff, &fi->i_compr_blocks);
>  		stat_sub_compr_blocks(inode, diff);
>  	}
>  	f2fs_mark_inode_dirty_sync(inode, true);
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index cc7f5670390f..adc4acad488a 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -564,7 +564,7 @@ void f2fs_truncate_data_blocks_range(struct dnode_of_data *dn, int count)
>  	bool compressed_cluster = false;
>  	int cluster_index = 0, valid_blocks = 0;
>  	int cluster_size = F2FS_I(dn->inode)->i_cluster_size;
> -	bool released = !F2FS_I(dn->inode)->i_compr_blocks;
> +	bool released = !atomic_read(&F2FS_I(dn->inode)->i_compr_blocks);
>  
>  	if (IS_INODE(dn->node_page) && f2fs_has_extra_attr(dn->inode))
>  		base = get_extra_isize(dn->inode);
> @@ -3436,7 +3436,7 @@ static int f2fs_get_compress_blocks(struct file *filp, unsigned long arg)
>  	if (!f2fs_compressed_file(inode))
>  		return -EINVAL;
>  
> -	blocks = F2FS_I(inode)->i_compr_blocks;
> +	blocks = atomic_read(&F2FS_I(inode)->i_compr_blocks);
>  	return put_user(blocks, (u64 __user *)arg);
>  }
>  
> @@ -3535,7 +3535,7 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)
>  	if (ret)
>  		goto out;
>  
> -	if (!F2FS_I(inode)->i_compr_blocks)
> +	if (!atomic_read(&F2FS_I(inode)->i_compr_blocks))
>  		goto out;
>  
>  	F2FS_I(inode)->i_flags |= F2FS_IMMUTABLE_FL;
> @@ -3588,14 +3588,15 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)
>  
>  	if (ret >= 0) {
>  		ret = put_user(released_blocks, (u64 __user *)arg);
> -	} else if (released_blocks && F2FS_I(inode)->i_compr_blocks) {
> +	} else if (released_blocks &&
> +			atomic_read(&F2FS_I(inode)->i_compr_blocks)) {
>  		set_sbi_flag(sbi, SBI_NEED_FSCK);
>  		f2fs_warn(sbi, "%s: partial blocks were released i_ino=%lx "
> -			"iblocks=%llu, released=%u, compr_blocks=%llu, "
> +			"iblocks=%llu, released=%u, compr_blocks=%u, "
>  			"run fsck to fix.",
>  			__func__, inode->i_ino, inode->i_blocks,
>  			released_blocks,
> -			F2FS_I(inode)->i_compr_blocks);
> +			atomic_read(&F2FS_I(inode)->i_compr_blocks));
>  	}
>  
>  	return ret;
> @@ -3683,7 +3684,7 @@ static int f2fs_reserve_compress_blocks(struct file *filp, unsigned long arg)
>  	if (ret)
>  		return ret;
>  
> -	if (F2FS_I(inode)->i_compr_blocks)
> +	if (atomic_read(&F2FS_I(inode)->i_compr_blocks))
>  		goto out;
>  
>  	f2fs_balance_fs(F2FS_I_SB(inode), true);
> @@ -3747,14 +3748,15 @@ static int f2fs_reserve_compress_blocks(struct file *filp, unsigned long arg)
>  
>  	if (ret >= 0) {
>  		ret = put_user(reserved_blocks, (u64 __user *)arg);
> -	} else if (reserved_blocks && F2FS_I(inode)->i_compr_blocks) {
> +	} else if (reserved_blocks &&
> +			atomic_read(&F2FS_I(inode)->i_compr_blocks)) {
>  		set_sbi_flag(sbi, SBI_NEED_FSCK);
>  		f2fs_warn(sbi, "%s: partial blocks were released i_ino=%lx "
> -			"iblocks=%llu, reserved=%u, compr_blocks=%llu, "
> +			"iblocks=%llu, reserved=%u, compr_blocks=%u, "
>  			"run fsck to fix.",
>  			__func__, inode->i_ino, inode->i_blocks,
>  			reserved_blocks,
> -			F2FS_I(inode)->i_compr_blocks);
> +			atomic_read(&F2FS_I(inode)->i_compr_blocks));
>  	}
>  
>  	return ret;
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index 66969ae852b9..2ed935c13aed 100644
> --- a/fs/f2fs/inode.c
> +++ b/fs/f2fs/inode.c
> @@ -442,7 +442,8 @@ static int do_read_inode(struct inode *inode)
>  					(fi->i_flags & F2FS_COMPR_FL)) {
>  		if (F2FS_FITS_IN_INODE(ri, fi->i_extra_isize,
>  					i_log_cluster_size)) {
> -			fi->i_compr_blocks = le64_to_cpu(ri->i_compr_blocks);
> +			atomic_set(&fi->i_compr_blocks,
> +					le64_to_cpu(ri->i_compr_blocks));
>  			fi->i_compress_algorithm = ri->i_compress_algorithm;
>  			fi->i_log_cluster_size = ri->i_log_cluster_size;
>  			fi->i_cluster_size = 1 << fi->i_log_cluster_size;
> @@ -460,7 +461,7 @@ static int do_read_inode(struct inode *inode)
>  	stat_inc_inline_inode(inode);
>  	stat_inc_inline_dir(inode);
>  	stat_inc_compr_inode(inode);
> -	stat_add_compr_blocks(inode, F2FS_I(inode)->i_compr_blocks);
> +	stat_add_compr_blocks(inode, atomic_read(&fi->i_compr_blocks));
>  
>  	return 0;
>  }
> @@ -619,7 +620,8 @@ void f2fs_update_inode(struct inode *inode, struct page *node_page)
>  			F2FS_FITS_IN_INODE(ri, F2FS_I(inode)->i_extra_isize,
>  							i_log_cluster_size)) {
>  			ri->i_compr_blocks =
> -				cpu_to_le64(F2FS_I(inode)->i_compr_blocks);
> +				cpu_to_le64(atomic_read(
> +					&F2FS_I(inode)->i_compr_blocks));
>  			ri->i_compress_algorithm =
>  				F2FS_I(inode)->i_compress_algorithm;
>  			ri->i_log_cluster_size =
> @@ -768,7 +770,8 @@ void f2fs_evict_inode(struct inode *inode)
>  	stat_dec_inline_dir(inode);
>  	stat_dec_inline_inode(inode);
>  	stat_dec_compr_inode(inode);
> -	stat_sub_compr_blocks(inode, F2FS_I(inode)->i_compr_blocks);
> +	stat_sub_compr_blocks(inode,
> +			atomic_read(&F2FS_I(inode)->i_compr_blocks));
>  
>  	if (likely(!f2fs_cp_error(sbi) &&
>  				!is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 83bf9a02f83f..813aa207824c 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1011,6 +1011,7 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
>  
>  	/* Initialize f2fs-specific inode info */
>  	atomic_set(&fi->dirty_pages, 0);
> +	atomic_set(&fi->i_compr_blocks, 0);
>  	init_rwsem(&fi->i_sem);
>  	spin_lock_init(&fi->i_size_lock);
>  	INIT_LIST_HEAD(&fi->dirty_list);
> -- 
> 2.28.0.526.ge36021eeef-goog
> 
> 
> 
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