Re: [PATCH v3 6/7] smb/client: fix stale page cache in insert/collapse range

[Paulo Alcantara <pc@manguebit.org>]

Huiwen He <huiwen.he@linux.dev> writes:

> From: Huiwen He <hehuiwen@kylinos.cn>
>
> smb3_insert_range() and smb3_collapse_range() use
> truncate_pagecache_range() to invalidate the affected page cache.
> However, if off or old_eof is not page-aligned, the boundary pages are
> only partially zeroed and remain uptodate. As a result, the client may
> return stale data after a successful insert/collapse range operation.
>
> For example, with 4K pages:
>
>     page 0          page 1          page 2
>     0------4K       4K------8K      8K------12K
>        ^                                ^
>     off=2K                       old_eof=10K
>
> Page 1 is removed from the page cache, while the boundary pages are
> only partially zeroed. After COPYCHUNK moves the data on the server,
> these cached pages may still return stale data.
>
> This can be reproduced on a CIFS mount:
>
>     bash -c '
>             FILE=/mnt/scratch/repro
>
>             # Use a 6 KiB file so EOF is not page-aligned.
>             dd if=/dev/urandom of=/tmp/src bs=1K count=6 status=none
>
>             # Expected: a 4 KiB hole followed by the original data.
>             rm -f /tmp/expected
>             truncate -s 4K /tmp/expected
>             cat /tmp/src >> /tmp/expected
>
>             cp /tmp/src "$FILE"
>
>             # Prime the page cache before moving data on the server.
>             cat "$FILE" > /dev/null
>
>             fallocate --insert-range -o 0 -l 4K "$FILE"
>
>             if cmp -s /tmp/expected "$FILE"; then
>                     echo "readback: OK"
>             else
>                     echo "readback: STALE DATA"
>             fi
>     '
>
> Fix this by writing back dirty data and discarding the page cache from
> the start of the page containing off to EOF before moving data on the
> server.
> ...

Applied.