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Subject: Re: [f2fs-dev] [PATCH] f2fs: change i_compr_blocks of inode to atomic
 value
To:     Daeho Jeong <daeho43@gmail.com>, <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>, <kernel-team@android.com>
CC:     Daeho Jeong <daehojeong@google.com>
References: <20200902062910.4061083-1-daeho43@gmail.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <822bd3b7-4354-1c61-07c4-6a57b3616ea8@huawei.com>
Date:   Thu, 3 Sep 2020 09:08:05 +0800
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On 2020/9/2 14:29, 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.
> 
> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> ---
>   fs/f2fs/f2fs.h  | 15 +++++++++------
>   fs/f2fs/file.c  | 18 ++++++++++--------
>   fs/f2fs/inode.c | 11 +++++++----
>   fs/f2fs/super.c |  1 +
>   4 files changed, 27 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index f60414805e05..633957e14944 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 */
> +	atomic64_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 */
> @@ -3933,14 +3933,16 @@ static inline void set_compress_context(struct inode *inode)
>   static inline u64 f2fs_disable_compressed_file(struct inode *inode)
>   {
>   	struct f2fs_inode_info *fi = F2FS_I(inode);
> +	u64 i_compr_blocks;
>   
>   	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;
Caller doesn't care how many compr_blocks this inode has saved, so we can just
return 1 here.

> +		i_compr_blocks = atomic64_read(&fi->i_compr_blocks);
> +		if (i_compr_blocks)
> +			return i_compr_blocks;
>   	}
>   
>   	fi->i_flags &= ~F2FS_COMPR_FL;
> @@ -4057,16 +4059,17 @@ 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 && !atomic64_read(&fi->i_compr_blocks))
>   		return;
>   
>   	if (add) {
> -		F2FS_I(inode)->i_compr_blocks += diff;
> +		atomic64_add(diff, &fi->i_compr_blocks);
>   		stat_add_compr_blocks(inode, diff);
>   	} else {
> -		F2FS_I(inode)->i_compr_blocks -= diff;
> +		atomic64_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..4e4e369b97e5 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 = !atomic64_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 = atomic64_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 (!atomic64_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 &&
> +			atomic64_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, "
>   			"run fsck to fix.",
>   			__func__, inode->i_ino, inode->i_blocks,
>   			released_blocks,
> -			F2FS_I(inode)->i_compr_blocks);
> +			atomic64_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 (atomic64_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 &&
> +			atomic64_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, "
>   			"run fsck to fix.",
>   			__func__, inode->i_ino, inode->i_blocks,
>   			reserved_blocks,
> -			F2FS_I(inode)->i_compr_blocks);
> +			atomic64_read(&F2FS_I(inode)->i_compr_blocks));
>   	}
>   
>   	return ret;
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index 66969ae852b9..e86857af9699 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);
> +			atomic64_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, atomic64_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(atomic64_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,
> +			atomic64_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..65613500e1ab 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);
> +	atomic64_set(&fi->i_compr_blocks, 0);
>   	init_rwsem(&fi->i_sem);
>   	spin_lock_init(&fi->i_size_lock);
>   	INIT_LIST_HEAD(&fi->dirty_list);
>