On Mon 05-10-20 01:14:54, Josh Triplett wrote:
> Ran into an ext4 regression when testing upgrades to 5.9-rc kernels:
>
> Commit e7bfb5c9bb3d ("ext4: handle add_system_zone() failure in
> ext4_setup_system_zone()") breaks mounting of read-only ext4 filesystems
> with intentionally overlapping bitmap blocks.
>
> On an always-read-only filesystem explicitly marked with
> EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS, prior to that commit, it's safe to
> point all the block and inode bitmaps to a single block of all 1s,
> because a read-only filesystem will never allocate or free any blocks or
> inodes.
>
> However, after that commit, the block validity check rejects such
> filesystems with -EUCLEAN and "failed to initialize system zone (-117)".
> This causes systems that previously worked correctly to fail when
> upgrading to v5.9-rc2 or later.
>
> This was obviously a bugfix, and I'm not suggesting that it should be
> reverted; it looks like this effectively worked by accident before,
> because the block_validity check wasn't fully functional. However, this
> does break real systems, and I'd like to get some kind of regression fix
> in before 5.9 final if possible. I think it would suffice to make
> block_validity default to false if and only if
> EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS is set.
>
> Does that seem like a reasonable fix?
>
> Here's a quick sketch of a patch, which I've tested and confirmed to
> work:
>
> ----- 8< -----
> Subject: [PATCH] Fix ext4 regression in v5.9-rc2 on ro fs with overlapped bitmaps
>
> Commit e7bfb5c9bb3d ("ext4: handle add_system_zone() failure in
> ext4_setup_system_zone()") breaks mounting of read-only ext4 filesystems
> with intentionally overlapping bitmap blocks.
>
> On an always-read-only filesystem explicitly marked with
> EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS, prior to that commit, it's safe to
> point all the block and inode bitmaps to a single block of all 1s,
> because a read-only filesystem will never allocate or free any blocks or
> inodes.
>
> However, after that commit, the block validity check rejects such
> filesystems with -EUCLEAN and "failed to initialize system zone (-117)".
> This causes systems that previously worked correctly to fail when
> upgrading to v5.9-rc2 or later.
>
> Fix this by defaulting block_validity to off when
> EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS is set.
>
> Signed-off-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> Fixes: e7bfb5c9bb3d ("ext4: handle add_system_zone() failure in ext4_setup_system_zone()")
The patch looks fine to me. Thanks for fixing this and for educating me
about the feature :) You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/ext4/ext4.h | 2 ++
> fs/ext4/super.c | 3 ++-
> 2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 523e00d7b392..7874028fa864 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1834,6 +1834,7 @@ static inline bool ext4_verity_in_progress(struct inode *inode)
> #define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM 0x0400
> #define EXT4_FEATURE_RO_COMPAT_READONLY 0x1000
> #define EXT4_FEATURE_RO_COMPAT_PROJECT 0x2000
> +#define EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS 0x4000
> #define EXT4_FEATURE_RO_COMPAT_VERITY 0x8000
>
> #define EXT4_FEATURE_INCOMPAT_COMPRESSION 0x0001
> @@ -1930,6 +1931,7 @@ EXT4_FEATURE_RO_COMPAT_FUNCS(bigalloc, BIGALLOC)
> EXT4_FEATURE_RO_COMPAT_FUNCS(metadata_csum, METADATA_CSUM)
> EXT4_FEATURE_RO_COMPAT_FUNCS(readonly, READONLY)
> EXT4_FEATURE_RO_COMPAT_FUNCS(project, PROJECT)
> +EXT4_FEATURE_RO_COMPAT_FUNCS(shared_blocks, SHARED_BLOCKS)
> EXT4_FEATURE_RO_COMPAT_FUNCS(verity, VERITY)
>
> EXT4_FEATURE_INCOMPAT_FUNCS(compression, COMPRESSION)
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index ea425b49b345..f57a7e966e44 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3954,7 +3954,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> else
> set_opt(sb, ERRORS_RO);
> /* block_validity enabled by default; disable with noblock_validity */
> - set_opt(sb, BLOCK_VALIDITY);
> + if (!ext4_has_feature_shared_blocks(sb))
> + set_opt(sb, BLOCK_VALIDITY);
> if (def_mount_opts & EXT4_DEFM_DISCARD)
> set_opt(sb, DISCARD);
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
