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From: Yosry Ahmed <yosry@kernel.org>
Date: Thu, 22 Oct 2026 15:19:45 -0700
Message-ID: <CAO9r8zP2cNFQ=CW4LZ0ttXtr3Q2PLs4A=rgMDZoSo=JVNuYpKA@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 8:34=E2=80=AFAM Yosry Ahmed <yosry@kernel.org> wrot=
e:
>
> On Thu, Oct 22, 2026 at 1:14=E2=80=AFAM Herbert Xu <herbert@gondor.apana.=
org.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,=
 or
> > > 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 singl=
e
> > > pages, such as in zswap) as well as lz4, lz4hc, lzo, and lzo-rle retu=
rn
> > > -EINVAL instead of -ENOSPC on destination buffer overflow.
> > >
> > > For users such as zswap, which reduced its per-CPU compression buffer=
 to
> > > a single page in commit 0b1bf60c324a ("mm/zswap: reduce the size of t=
he
> > > compression buffer to a single page"), incompressible pages typically
> > > overflow the PAGE_SIZE destination buffer due to compressor header/to=
ken
> > > overhead. Because these compressors return -EINVAL rather than -ENOSP=
C,
> > > zswap cannot distinguish a destination buffer overflow from a compres=
sor
> > > failure, causing broken debugfs error accounting (reject_compress_fai=
l
> > > 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?

Patch 2 will be re-sent separately, so please feel free to take this
patch as-is. Thanks!