Re: [PATCH v3] f2fs: fix to keep isolation of atomic write

[Jaegeuk Kim]

On 04/12, Chao Yu wrote:
> As Yi Chen reported, there is a potential race case described as below:
> 
> Thread A			Thread B
> - f2fs_ioc_start_atomic_write
> 				- mkwrite
> 				 - set_page_dirty
> 				  - f2fs_set_page_private(page, 0)
>  - set_inode_flag(FI_ATOMIC_FILE)
> 				- mkwrite same page
> 				 - set_page_dirty
> 				  - f2fs_register_inmem_page
> 				   - f2fs_set_page_private(ATOMIC_WRITTEN_PAGE)
> 				     failed due to PagePrivate flag has been set
> 				   - list_add_tail
> 				- truncate_inode_pages
> 				 - f2fs_invalidate_page
> 				  - clear page private but w/o remove it from
> 				    inmem_list
> 				 - set page->mapping to NULL
> - f2fs_ioc_commit_atomic_write
>  - __f2fs_commit_inmem_pages
>    - __revoke_inmem_pages
>     - f2fs_put_page panic as page->mapping is NULL
> 
> The root cause is we missed to keep isolation of atomic write in the case
> of start_atomic_write vs mkwrite, let start_atomic_write helds i_mmap_sem
> lock to avoid this issue.

My only concern is performance regression. Could you please verify the numbers?

> 
> Reported-by: Yi Chen <chenyi77@xxxxxxxxxx>
> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> ---
> v3:
> - rebase to last dev branch
> - update commit message because this patch fixes a different racing issue
> of atomic write
>  fs/f2fs/file.c    | 3 +++
>  fs/f2fs/segment.c | 6 ++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index d697c8900fa7..6284b2f4a60b 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -2054,6 +2054,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>  		goto out;
>  
>  	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> +	down_write(&F2FS_I(inode)->i_mmap_sem);
>  
>  	/*
>  	 * Should wait end_io to count F2FS_WB_CP_DATA correctly by
> @@ -2064,6 +2065,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>  			  inode->i_ino, get_dirty_pages(inode));
>  	ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
>  	if (ret) {
> +		up_write(&F2FS_I(inode)->i_mmap_sem);
>  		up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>  		goto out;
>  	}
> @@ -2077,6 +2079,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>  	/* add inode in inmem_list first and set atomic_file */
>  	set_inode_flag(inode, FI_ATOMIC_FILE);
>  	clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> +	up_write(&F2FS_I(inode)->i_mmap_sem);
>  	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>  
>  	f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 0cb1ca88d4aa..78c8342f52fd 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -325,6 +325,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>  	struct f2fs_inode_info *fi = F2FS_I(inode);
>  
>  	do {
> +		down_write(&F2FS_I(inode)->i_mmap_sem);
>  		mutex_lock(&fi->inmem_lock);
>  		if (list_empty(&fi->inmem_pages)) {
>  			fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> @@ -339,11 +340,13 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>  			spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>  
>  			mutex_unlock(&fi->inmem_lock);
> +			up_write(&F2FS_I(inode)->i_mmap_sem);
>  			break;
>  		}
>  		__revoke_inmem_pages(inode, &fi->inmem_pages,
>  						true, false, true);
>  		mutex_unlock(&fi->inmem_lock);
> +		up_write(&F2FS_I(inode)->i_mmap_sem);
>  	} while (1);
>  }
>  
> @@ -468,6 +471,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>  	f2fs_balance_fs(sbi, true);
>  
>  	down_write(&fi->i_gc_rwsem[WRITE]);
> +	down_write(&F2FS_I(inode)->i_mmap_sem);
>  
>  	f2fs_lock_op(sbi);
>  	set_inode_flag(inode, FI_ATOMIC_COMMIT);
> @@ -479,6 +483,8 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>  	clear_inode_flag(inode, FI_ATOMIC_COMMIT);
>  
>  	f2fs_unlock_op(sbi);
> +
> +	up_write(&F2FS_I(inode)->i_mmap_sem);
>  	up_write(&fi->i_gc_rwsem[WRITE]);
>  
>  	return err;
> -- 
> 2.29.2