RE: [PATCH v1 1/2] mm: zswap: Per-CPU acomp_ctx resources exist from pool creation to deletion.

["Sridhar, Kanchana P" <kanchana.p.sridhar@intel.com>]

> -----Original Message-----
> From: Al Viro <viro@ftp.linux.org.uk> On Behalf Of Al Viro
> Sent: Monday, July 7, 2025 3:06 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> hannes@cmpxchg.org; yosry.ahmed@linux.dev; nphamcs@gmail.com;
> chengming.zhou@linux.dev; usamaarif642@gmail.com;
> ryan.roberts@arm.com; 21cnbao@gmail.com;
> ying.huang@linux.alibaba.com; akpm@linux-foundation.org;
> senozhatsky@chromium.org; Feghali, Wajdi K <wajdi.k.feghali@intel.com>;
> Gopal, Vinodh <vinodh.gopal@intel.com>
> Subject: Re: [PATCH v1 1/2] mm: zswap: Per-CPU acomp_ctx resources exist
> from pool creation to deletion.
> 
> On Mon, Jul 07, 2025 at 01:13:14PM -0700, Kanchana P Sridhar wrote:
> 
> > +static void acomp_ctx_dealloc(struct crypto_acomp_ctx *acomp_ctx)
> > +{
> > +	if (IS_ERR_OR_NULL(acomp_ctx))
> 
> Ugh.
> 
> > +		return;
> > +
> > +	if (!IS_ERR_OR_NULL(acomp_ctx->req))
> 
> Ugh.
> 
> > +		acomp_request_free(acomp_ctx->req);
> > +
> > +	if (!IS_ERR_OR_NULL(acomp_ctx->acomp))
> 
> Ugh.
> 
> > +		crypto_free_acomp(acomp_ctx->acomp);
> > +
> > +	kfree(acomp_ctx->buffer);
> 
> Just what are those IS_ERR_OR_NULL about?  Is it IS_ERR() or is it NULL?
> Either has valid uses, but mixing them is not something you do without a
> good reason; there are valid calling conventions that allow all three of
> "address of an object", NULL and ERR_PTR(-E...), but that's not something
> you do just in case - there should be an explanation of what's going on.

I hope my reply to Nhat clarifies and provides some more context.
In summary, the IS_ERR_OR_NULL() is preserving existing mainline code in
zswap_cpu_comp_dead() in the new acomp_ctx_dealloc(). There is no
teardown callback, i.e., zswap_cpu_comp_dead() with this patch series.

Thanks,
Kanchana