On Sun, Dec 13, 2020 at 08:27:13AM -0500, Jeff Layton wrote:
> Peek at the upper layer's errseq_t at mount time for volatile mounts,
> and record it in the per-sb info. In sync_fs, check for an error since
> the recorded point and set it in the overlayfs superblock if there was
> one.
>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/overlayfs/ovl_entry.h | 1 +
> fs/overlayfs/super.c | 14 +++++++++++---
> 2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 1b5a2094df8e..fcfcc3951973 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -79,6 +79,7 @@ struct ovl_fs {
> atomic_long_t last_ino;
> /* Whiteout dentry cache */
> struct dentry *whiteout;
> + errseq_t err_mark;
> };
>
> static inline struct vfsmount *ovl_upper_mnt(struct ovl_fs *ofs)
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 290983bcfbb3..2985d2752970 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -264,8 +264,13 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
> if (!ovl_upper_mnt(ofs))
> return 0;
>
> - if (!ovl_should_sync(ofs))
> - return 0;
> + if (!ovl_should_sync(ofs)) {
> + /* Propagate errors from upper to overlayfs */
> + ret = errseq_check(&upper_sb->s_wb_err, ofs->err_mark);
> + errseq_set(&sb->s_wb_err, ret);
> + return ret;
> + }
> +
> /*
> * Not called for sync(2) call or an emergency sync (SB_I_SKIP_SYNC).
> * All the super blocks will be iterated, including upper_sb.
> @@ -1945,8 +1950,11 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
>
> sb->s_stack_depth = ovl_upper_mnt(ofs)->mnt_sb->s_stack_depth;
> sb->s_time_gran = ovl_upper_mnt(ofs)->mnt_sb->s_time_gran;
> -
> }
> +
> + if (ofs->config.ovl_volatile)
> + ofs->err_mark = errseq_peek(&ovl_upper_mnt(ofs)->mnt_sb->s_wb_err);
> +
> oe = ovl_get_lowerstack(sb, splitlower, numlower, ofs, layers);
> err = PTR_ERR(oe);
> if (IS_ERR(oe))
> --
> 2.29.2
>
I've tested this with the following scenarios, seems to work:
Test:
1. Mount ext2 on /mnt/loop, and cause a writeback error
2. Verify syncfs on /mnt/loop shows error
3. Mount volatile filesystem
4. Create file on volatile filesystem, and verify that I can syncfs it without error
---
Fork:
5a. Create a file on overlayfs, and generate a writeback error
6a. Syncfs overlayfs.
7a. Create a new file on overlayfs, and syncfs, and verify it returns error
---
5b. Create a file on loop back, and generate a writeback error
6b. Sync said file
7b. Verify syncfs on loop returns error once, and then success on next attempts
8b. Verify all syncfs on overlayfs now fail
---
5c. Create file on overlayfs, and generate a writeback error
6c. Sync overlayfs, and verify all syncs are failures
7c. Verify syncfs on loop fails once.
