Re: [PATCH] fstests: btrfs: verify the read behavior of compressed inline extent

[David Disseldorp <ddiss@suse.de>]

On Tue, 23 Jan 2024 14:19:08 +1030, Qu Wenruo wrote:

> [BUG]
> There is a report about reading a zstd compressed inline file extent
> would lead to either a VM_BUG_ON() crash, or lead to incorrect file
> content.
> 
> [CAUSE]
> The root cause is a incorrect memcpy_to_page() call, which uses
> incorrect page offset, and can lead to either the VM_BUG_ON() as we may
> write beyond the page boundary, or writes into the incorrect offset of
> the page.
> 
> [TEST CASE]
> The test case would:
> 
> - Mount with the specified compress algorithm
> - Create a 4K file
> - Verify the 4K file is all inlined and compressed
> - Verify the content of the initial write
> - Cycle mount to drop all the page cache
> - Verify the content of the file again
> - Unmount and fsck the fs
> 
> This workload would be applied to all supported compression algorithms.
> And it can catch the problem correctly by triggering VM_BUG_ON(), as our
> workload would result decompressed extent size to be 4K, and would
> trigger the VM_BUG_ON() 100%.
> And with the revert or the new fix, the test case can pass safely.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  tests/btrfs/310     | 81 +++++++++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/310.out |  2 ++
>  2 files changed, 83 insertions(+)
>  create mode 100755 tests/btrfs/310
>  create mode 100644 tests/btrfs/310.out
> 
> diff --git a/tests/btrfs/310 b/tests/btrfs/310
> new file mode 100755
> index 00000000..b514a8bc
> --- /dev/null
> +++ b/tests/btrfs/310
> @@ -0,0 +1,81 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2024 SUSE Linux Products GmbH. All Rights Reserved.
> +#
> +# FS QA Test 310
> +#
> +# Make sure reading on an compressed inline extent is behaving correctly
> +#
> +. ./common/preamble
> +_begin_fstest auto quick compress
> +
> +# Import common functions.
> +# . ./common/filter
> +
> +# real QA test starts here
> +
> +# Modify as appropriate.
> +_supported_fs btrfs
> +_require_scratch
> +
> +# This test require inlined compressed extents creation, and all the writes
> +# are designed for 4K sector size.
> +_require_btrfs_inline_extents_creation
> +_require_btrfs_support_sectorsize 4096

Hopefully coverage can be expanded in future to cover some other sector
sizes. This looks fine for now:

Reviewed-by: David Disseldorp <ddiss@suse.de>