This patchset first removes redundant checks on the acomp_ctx and its
"req" member in zswap_cpu_comp_dead().

Next, it persists the zswap pool's per-CPU acomp_ctx resources to
last until the pool is destroyed. It then simplifies the per-CPU
acomp_ctx mutex locking in zswap_compress()/zswap_decompress().

Code comments added after allocation and before checking to deallocate
the per-CPU acomp_ctx's members, based on expected crypto API return
values and zswap changes this patchset makes.

Patch 2 is an independent submission of patch 23 from [1], to
facilitate merging.

[1]: https://patchwork.kernel.org/project/linux-mm/list/?series=1046677

Changes since v1:
=================
1) Made the changes to eliminate redundant checks on
   acomp_ctx/acomp_ctx->req in zswap_cpu_comp_dead(), per Yosry.
2) Renamed acomp_ctx_dealloc() to acomp_ctx_free(), per Yosry.
3) Incorporated suggestions from Yosry and Sashiko to reset the
   acomp_ctx's members to NULL after freeing them, to prevent UAF and
   double free issues.
4) Replaced v1's patch 2 with v2's patch 1.


Kanchana P. Sridhar (2):
  mm: zswap: Remove redundant checks in zswap_cpu_comp_dead().
  mm: zswap: Tie per-CPU acomp_ctx lifetime to the pool.

 mm/zswap.c | 182 +++++++++++++++++++++++++----------------------------
 1 file changed, 85 insertions(+), 97 deletions(-)

-- 
2.39.5

On Mon, 16 Mar 2026 18:48:00 -0700 "Kanchana P. Sridhar" <kanchanapsridhar2026@gmail.com> wrote:

> This patchset first removes redundant checks on the acomp_ctx and its
> "req" member in zswap_cpu_comp_dead().
> 
> Next, it persists the zswap pool's per-CPU acomp_ctx resources to
> last until the pool is destroyed. It then simplifies the per-CPU
> acomp_ctx mutex locking in zswap_compress()/zswap_decompress().
> 
> Code comments added after allocation and before checking to deallocate
> the per-CPU acomp_ctx's members, based on expected crypto API return
> values and zswap changes this patchset makes.
> 
> Patch 2 is an independent submission of patch 23 from [1], to
> facilitate merging.

Thanks.

What happened with "mm: zswap: Consistently use IS_ERR_OR_NULL() to
check acomp_ctx resources"?  Still relevant?

https://lkml.kernel.org/r/20260314051632.17931-3-kanchanapsridhar2026@gmail.com

On Tue, Mar 17, 2026 at 12:45 PM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> On Mon, 16 Mar 2026 18:48:00 -0700 "Kanchana P. Sridhar" <kanchanapsridhar2026@gmail.com> wrote:
>
> > This patchset first removes redundant checks on the acomp_ctx and its
> > "req" member in zswap_cpu_comp_dead().
> >
> > Next, it persists the zswap pool's per-CPU acomp_ctx resources to
> > last until the pool is destroyed. It then simplifies the per-CPU
> > acomp_ctx mutex locking in zswap_compress()/zswap_decompress().
> >
> > Code comments added after allocation and before checking to deallocate
> > the per-CPU acomp_ctx's members, based on expected crypto API return
> > values and zswap changes this patchset makes.
> >
> > Patch 2 is an independent submission of patch 23 from [1], to
> > facilitate merging.
>
> Thanks.
>
> What happened with "mm: zswap: Consistently use IS_ERR_OR_NULL() to
> check acomp_ctx resources"?  Still relevant?
>
> https://lkml.kernel.org/r/20260314051632.17931-3-kanchanapsridhar2026@gmail.com

We decided to drop it (and patch 1 here kinda sorta takes its place):
https://lore.kernel.org/all/CACpmpoeo0LhxkoA5Wx6q+9=2scn_az0u=3bar-JgBvTA-ZBkZg@mail.gmail.com/

On Tue, Mar 17, 2026 at 12:48 PM Yosry Ahmed <yosry@kernel.org> wrote:
>
> On Tue, Mar 17, 2026 at 12:45 PM Andrew Morton
> <akpm@linux-foundation.org> wrote:
> >
> > On Mon, 16 Mar 2026 18:48:00 -0700 "Kanchana P. Sridhar" <kanchanapsridhar2026@gmail.com> wrote:
> >
> > > This patchset first removes redundant checks on the acomp_ctx and its
> > > "req" member in zswap_cpu_comp_dead().
> > >
> > > Next, it persists the zswap pool's per-CPU acomp_ctx resources to
> > > last until the pool is destroyed. It then simplifies the per-CPU
> > > acomp_ctx mutex locking in zswap_compress()/zswap_decompress().
> > >
> > > Code comments added after allocation and before checking to deallocate
> > > the per-CPU acomp_ctx's members, based on expected crypto API return
> > > values and zswap changes this patchset makes.
> > >
> > > Patch 2 is an independent submission of patch 23 from [1], to
> > > facilitate merging.
> >
> > Thanks.
> >
> > What happened with "mm: zswap: Consistently use IS_ERR_OR_NULL() to
> > check acomp_ctx resources"?  Still relevant?
> >
> > https://lkml.kernel.org/r/20260314051632.17931-3-kanchanapsridhar2026@gmail.com
>
> We decided to drop it (and patch 1 here kinda sorta takes its place):
> https://lore.kernel.org/all/CACpmpoeo0LhxkoA5Wx6q+9=2scn_az0u=3bar-JgBvTA-ZBkZg@mail.gmail.com/

Thanks for the clarification, Yosry!

Thanks Andrew, for adding the two patches in v2 to mm-new! Thanks also
for obsoleting the "mm: zswap: Consistently use IS_ERR_OR_NULL() to
check acomp_ctx resources" patch - we decided to replace this with the
"[v2,1/2] mm: zswap: Remove redundant checks in
zswap_cpu_comp_dead().", which makes the acomp_ctx consistency checks
changes in the original mainline code, before refactoring that code
into the new acomp_ctx_free() in "[v2,2/2] mm: zswap: Tie per-CPU
acomp_ctx lifetime to the pool."

Best regards,
Kanchana