linux.git/fs/btrfs/zstd.c, branch v6.9

btrfs: zstd: fix and simplify the inline extent decompression (v2)

2024-03-04T15:24:46+00:00

Note: this is a fixed version that was previously reverted as
e01a83e12604 ("Revert "btrfs: zstd: fix and simplify the inline extent
decompression""), with fixed parameters to memzero_page().

[BUG]
If we have a filesystem with 4k sectorsize, and an inlined compressed
extent created like this:

	item 4 key (257 INODE_ITEM 0) itemoff 15863 itemsize 160
		generation 8 transid 8 size 4096 nbytes 4096
		block group 0 mode 100600 links 1 uid 0 gid 0 rdev 0
		sequence 1 flags 0x0(none)
	item 5 key (257 INODE_REF 256) itemoff 15839 itemsize 24
		index 2 namelen 14 name: source_inlined
	item 6 key (257 EXTENT_DATA 0) itemoff 15770 itemsize 69
		generation 8 type 0 (inline)
		inline extent data size 48 ram_bytes 4096 compression 3 (zstd)

Then trying to reflink that extent in an aarch64 system with 64K page
size, the reflink would just fail:

  # xfs_io -f -c "reflink $mnt/source_inlined 0 60k 4k" $mnt/dest
  XFS_IOC_CLONE_RANGE: Input/output error

[CAUSE]
In zstd_decompress(), we didn't treat @start_byte as just a page offset,
but also use it as an indicator on whether we should error out, without
any proper explanation (this is copied from other decompression code).

In reality, for subpage cases, although @start_byte can be non-zero,
we should never switch input/output buffer nor error out, since the whole
input/output buffer should never exceed one sector, thus we should not
need to do any buffer switch.

Thus the current code using @start_byte as a condition to switch
input/output buffer or finish the decompression is completely incorrect.

[FIX]
The fix involves several modification:

- Rename @start_byte to @dest_pgoff to properly express its meaning

- Use @sectorsize other than PAGE_SIZE to properly initialize the
  output buffer size

- Use correct destination offset inside the destination page

- Simplify the main loop
  Since the input/output buffer should never switch, we only need one
  zstd_decompress_stream() call.

- Consider early end as an error

After the fix, even on 64K page sized aarch64, above reflink now
works as expected:

  # xfs_io -f -c "reflink $mnt/source_inlined 0 60k 4k" $mnt/dest
  linked 4096/4096 bytes at offset 61440

And results the correct file layout:

	item 9 key (258 INODE_ITEM 0) itemoff 15542 itemsize 160
		generation 10 transid 10 size 65536 nbytes 4096
		block group 0 mode 100600 links 1 uid 0 gid 0 rdev 0
		sequence 1 flags 0x0(none)
	item 10 key (258 INODE_REF 256) itemoff 15528 itemsize 14
		index 3 namelen 4 name: dest
	item 11 key (258 XATTR_ITEM 3817753667) itemoff 15445 itemsize 83
		location key (0 UNKNOWN.0 0) type XATTR
		transid 10 data_len 37 name_len 16
		name: security.selinux
		data unconfined_u:object_r:unlabeled_t:s0
	item 12 key (258 EXTENT_DATA 61440) itemoff 15392 itemsize 53
		generation 10 type 1 (regular)
		extent data disk byte 13631488 nr 4096
		extent data offset 0 nr 4096 ram 4096
		extent compression 0 (none)

Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: remove unused included headers

2024-03-04T15:24:46+00:00

With help of neovim, LSP and clangd we can identify header files that
are not actually needed to be included in the .c files. This is focused
only on removal (with minor fixups), further cleanups are possible but
will require doing the header files properly with forward declarations,
minimized includes and include-what-you-use care.

Reviewed-by: Josef Bacik 
Signed-off-by: David Sterba

Revert "btrfs: zstd: fix and simplify the inline extent decompression"

2024-01-22T23:39:01+00:00

This reverts commit 1e7f6def8b2370ecefb54b3c8f390ff894b0c51b.

It causes my machine to not even boot, and Klara Modin reports that the
cause is that small zstd-compressed files return garbage when read.

Reported-by: Klara Modin 
Link: https://lore.kernel.org/linux-btrfs/CABq1_vj4GpUeZpVG49OHCo-3sdbe2-2ROcu_xDvUG-6-5zPRXg@mail.gmail.com/
Reported-and-bisected-by: Linus Torvalds 
Acked-by: David Sterba 
Cc: Qu Wenruo 
Signed-off-by: Linus Torvalds

btrfs: zstd: fix and simplify the inline extent decompression

2024-01-18T22:35:35+00:00

[BUG]
If we have a filesystem with 4k sectorsize, and an inlined compressed
extent created like this:

	item 4 key (257 INODE_ITEM 0) itemoff 15863 itemsize 160
		generation 8 transid 8 size 4096 nbytes 4096
		block group 0 mode 100600 links 1 uid 0 gid 0 rdev 0
		sequence 1 flags 0x0(none)
	item 5 key (257 INODE_REF 256) itemoff 15839 itemsize 24
		index 2 namelen 14 name: source_inlined
	item 6 key (257 EXTENT_DATA 0) itemoff 15770 itemsize 69
		generation 8 type 0 (inline)
		inline extent data size 48 ram_bytes 4096 compression 3 (zstd)

Then trying to reflink that extent in an aarch64 system with 64K page
size, the reflink would just fail:

  # xfs_io -f -c "reflink $mnt/source_inlined 0 60k 4k" $mnt/dest
  XFS_IOC_CLONE_RANGE: Input/output error

[CAUSE]
In zstd_decompress(), we didn't treat @start_byte as just a page offset,
but also use it as an indicator on whether we should error out, without
any proper explanation (this is copied from other decompression code).

In reality, for subpage cases, although @start_byte can be non-zero,
we should never switch input/output buffer nor error out, since the whole
input/output buffer should never exceed one sector, thus we should not
need to do any buffer switch.

Thus the current code using @start_byte as a condition to switch
input/output buffer or finish the decompression is completely incorrect.

[FIX]
The fix involves several modification:

- Rename @start_byte to @dest_pgoff to properly express its meaning

- Use @sectorsize other than PAGE_SIZE to properly initialize the
  output buffer size

- Use correct destination offset inside the destination page

- Simplify the main loop
  Since the input/output buffer should never switch, we only need one
  zstd_decompress_stream() call.

- Consider early end as an error

After the fix, even on 64K page sized aarch64, above reflink now
works as expected:

  # xfs_io -f -c "reflink $mnt/source_inlined 0 60k 4k" $mnt/dest
  linked 4096/4096 bytes at offset 61440

And results the correct file layout:

	item 9 key (258 INODE_ITEM 0) itemoff 15542 itemsize 160
		generation 10 transid 10 size 65536 nbytes 4096
		block group 0 mode 100600 links 1 uid 0 gid 0 rdev 0
		sequence 1 flags 0x0(none)
	item 10 key (258 INODE_REF 256) itemoff 15528 itemsize 14
		index 3 namelen 4 name: dest
	item 11 key (258 XATTR_ITEM 3817753667) itemoff 15445 itemsize 83
		location key (0 UNKNOWN.0 0) type XATTR
		transid 10 data_len 37 name_len 16
		name: security.selinux
		data unconfined_u:object_r:unlabeled_t:s0
	item 12 key (258 EXTENT_DATA 61440) itemoff 15392 itemsize 53
		generation 10 type 1 (regular)
		extent data disk byte 13631488 nr 4096
		extent data offset 0 nr 4096 ram 4096
		extent compression 0 (none)

Signed-off-by: Qu Wenruo 
Reviewed-by: David Sterba 
Signed-off-by: David Sterba

btrfs: use page alloc/free wrappers for compression pages

2023-12-15T19:27:01+00:00

This is a preparation for managing compression pages in a cache-like
manner, instead of asking the allocator each time. The common allocation
and free wrappers are introduced and are functionally equivalent to the
current code.

The freeing helpers need to be carefully placed where the last reference
is dropped.  This is either after directly allocating (error handling)
or when there are no other users of the pages (after copying the contents).

It's safe to not use the helper and use put_page() that will handle the
reference count. Not using the helper means there's lower number of
pages that could be reused without passing them back to allocator.

Reviewed-by: Josef Bacik 
Signed-off-by: David Sterba

btrfs: reformat remaining kdoc style comments

2023-10-12T14:44:04+00:00

Function name in the comment does not bring much value to code not
exposed as API and we don't stick to the kdoc format anymore. Update
formatting of parameter descriptions.

Reviewed-by: Qu Wenruo 
Signed-off-by: David Sterba

btrfs: disable allocation warnings for compression workspaces

2023-06-19T11:59:34+00:00

The workspaces for compression are typically much larger than a page and
for high zstd levels in the range of megabytes. There's a fallback to
vmalloc but this can still fail (see the report).

Some of the workspaces are preallocated at module load time so we have a
safe fallback, otherwise when a new workspace is needed it's allocated
but if this fails then the process waits. Which means the warning is
only causing noise and we can use the GFP flag to disable it.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=217466
Signed-off-by: David Sterba

btrfs: move zero filling of compressed read bios into common code

2023-04-17T16:01:17+00:00

All algorithms have to fill the remainder of the orig_bio with zeroes,
so do it in common code.

Reviewed-by: Anand Jain 
Reviewed-by: Johannes Thumshirn 
Reviewed-by: Qu Wenruo 
Signed-off-by: Christoph Hellwig 
Signed-off-by: David Sterba

btrfs: constify input buffer parameter in compression code

2022-12-05T17:00:55+00:00

The input buffers passed down to compression must never be changed,
switch type to u8 as it's a raw byte buffer and use const.

Reviewed-by: Anand Jain 
Signed-off-by: David Sterba

btrfs: update function comments

2022-12-05T17:00:45+00:00

Update, reformat or reword function comments. This also removes the kdoc
marker so we don't get reports when the function name is missing.

Changes made:

- remove kdoc markers
- reformat the brief description to be a proper sentence
- reword to imperative voice
- align parameter list
- fix typos

Signed-off-by: David Sterba