Re: [PATCH AUTOSEL 6.12 09/19] btrfs: zlib: make the compression path to handle sector size < page size

[Sasha Levin]

On Mon, Nov 25, 2024 at 04:20:59PM +0100, David Sterba wrote:
> On Sun, Nov 24, 2024 at 07:38:44AM -0500, Sasha Levin wrote:
> > From: Qu Wenruo <wqu@xxxxxxxx>
> >
> > [ Upstream commit f6ebedb09bb276256e084196e2322562dc4aac10 ]
> >
> > Inside zlib_compress_folios(), each time we switch the input page cache,
> > the @start is increased by PAGE_SIZE.
> >
> > But for the incoming compression support for sector size < page size
> > (previously we support compression only when the range is fully page
> > aligned), this is not going to handle the following case:
> >
> >     0          32K         64K          96K
> >     |          |///////////||///////////|
> >
> > @start has the initial value 32K, indicating the start filepos of the
> > to-be-compressed range.
> >
> > And when grabbing the first page as input, we always call "start +=
> > PAGE_SIZE;".
> >
> > But since @start is starting at 32K, it will be increased by 64K,
> > resulting it to be 96K for the next range, causing incorrect input range
> > and corruption for the future subpage compression.
> >
> > Fix it by only increase @start by the input size.
> >
> > Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> > Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
>
> Please drop this patch from stable, it's preparatory work and has
> otherwise no effect.

Will do, thanks!

--
Thanks,
Sasha