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

Jaegeuk Kim
2021-04-13T03:27:12Z

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@huawei.com>
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> ---
> 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