Re: [PATCH v2] fstests: btrfs: verify the read behavior of compressed inline extent

Anand Jain
2024-01-30T03:27:17Z

On 1/28/24 04:44, 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>

Reviewed-by: Anand Jain <anand.jain@oracle.com>