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 <20261021205626.3286270-2-suseendranb@google.com> <atnFygk8xsQ-8Mj5@gondor.apana.org.au>
In-Reply-To: <atnFygk8xsQ-8Mj5@gondor.apana.org.au>
From: Yosry Ahmed <yosry@kernel.org>
Date: Thu, 22 Oct 2026 08:34:43 -0700
Message-ID: <CAO9r8zOtFTuPm_aR8wrzYsxzNGKQ9pUy76g0eNk_HsPmi6YW-A@mail.gmail.com>
Subject: Re: [PATCH 1/2] crypto: return -ENOSPC on compression destination overflow
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Suseendran Bhaskaran <suseendranb@google.com>, Andrew Morton <akpm@linux-foundation.org>, 
	"David S . Miller" <davem@davemloft.net>, Johannes Weiner <hannes@cmpxchg.org>, Nhat Pham <nphamcs@gmail.com>, 
	Chengming Zhou <chengming.zhou@linux.dev>, Nick Terrell <terrelln@fb.com>, 
	David Sterba <dsterba@suse.com>, SJ Park <sj@kernel.org>, Chris Li <chrisl@kernel.org>, 
	Giovanni Cabiddu <giovanni.cabiddu@intel.com>, 
	Suman Kumar Chakraborty <suman.kumar.chakraborty@intel.com>, linux-crypto@vger.kernel.org, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Thu, Oct 22, 2026 at 1:14=E2=80=AFAM Herbert Xu <herbert@gondor.apana.or=
g.au> wrote:
>
> On Wed, Oct 21, 2026 at 08:56:25PM +0000, Suseendran Bhaskaran wrote:
> > In the acomp/scomp compression interface, callers pass a bounded
> > destination buffer and rely on the return code to distinguish a
> > destination buffer overflow (incompressible input) from genuine
> > compressor failures (such as invalid parameters, uninitialized state, o=
r
> > hardware errors).
> >
> > While the multi-segment streaming path in zstd_compress(),
> > crypto/deflate.c, and lib/842/842_compress.c returns -ENOSPC when the
> > destination buffer runs out of space, the single-buffer path
> > zstd_compress_one() (taken when input and output are contiguous single
> > pages, such as in zswap) as well as lz4, lz4hc, lzo, and lzo-rle return
> > -EINVAL instead of -ENOSPC on destination buffer overflow.
> >
> > For users such as zswap, which reduced its per-CPU compression buffer t=
o
> > a single page in commit 0b1bf60c324a ("mm/zswap: reduce the size of the
> > compression buffer to a single page"), incompressible pages typically
> > overflow the PAGE_SIZE destination buffer due to compressor header/toke=
n
> > overhead. Because these compressors return -EINVAL rather than -ENOSPC,
> > zswap cannot distinguish a destination buffer overflow from a compresso=
r
> > failure, causing broken debugfs error accounting (reject_compress_fail
> > vs. reject_compress_poor) or masking real compressor errors.
> >
> > Update zstd_compress_one(), lz4, lz4hc, lzo, and lzo-rle to return
> > -ENOSPC when the compressed output overflows the destination buffer,
> > matching the streaming path in zstd_compress(), deflate, and 842.
> >
> > Fixes: f5ad93ffb541 ("crypto: zstd - convert to acomp")
> > Signed-off-by: Suseendran Bhaskaran <suseendranb@google.com>
> > ---
> >  crypto/lz4.c     | 2 +-
> >  crypto/lz4hc.c   | 2 +-
> >  crypto/lzo-rle.c | 2 +-
> >  crypto/lzo.c     | 2 +-
> >  crypto/zstd.c    | 5 ++++-
> >  5 files changed, 8 insertions(+), 5 deletions(-)
>
> I can take this patch through the cryptodev tree.  Is that OK with
> you Yosry?

Thanks Herbert. I think we should wait to see how patch #2 turns out.
If I understand correctly, as of now patch #2 keys off -ENOSPC to make
a behavioral change in zswap, so the zswap patch would need to land
*after* this patch. Unless you want to fast track this to Linus right
away?