There are presently redundant checks on the per-CPU acomp_ctx and it's
"req" member in zswap_cpu_comp_dead(): redundant because they are
inconsistent with zswap_pool_create() handling of failure in allocating
the acomp_ctx, and with the expected NULL return value from the
acomp_request_alloc() API when it fails to allocate an acomp_req.

Fix these by converting to them to be NULL checks.

Add comments in zswap_cpu_comp_prepare() clarifying the expected return
values of the crypto_alloc_acomp_node() and acomp_request_alloc() API.

Suggested-by: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Kanchana P. Sridhar <kanchanapsridhar2026@gmail.com>
---
 mm/zswap.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index bdd24430f6ff..8ac38f1d0469 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -749,6 +749,10 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
 		goto fail;
 	}
 
+	/*
+	 * In case of an error, crypto_alloc_acomp_node() returns an
+	 * error pointer, never NULL.
+	 */
 	acomp = crypto_alloc_acomp_node(pool->tfm_name, 0, 0, cpu_to_node(cpu));
 	if (IS_ERR(acomp)) {
 		pr_err("could not alloc crypto acomp %s : %pe\n",
@@ -757,6 +761,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
 		goto fail;
 	}
 
+	/* acomp_request_alloc() returns NULL in case of an error. */
 	req = acomp_request_alloc(acomp);
 	if (!req) {
 		pr_err("could not alloc crypto acomp_request %s\n",
@@ -802,7 +807,7 @@ static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node)
 	struct crypto_acomp *acomp;
 	u8 *buffer;
 
-	if (IS_ERR_OR_NULL(acomp_ctx))
+	if (!acomp_ctx)
 		return 0;
 
 	mutex_lock(&acomp_ctx->mutex);
@@ -817,8 +822,11 @@ static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node)
 	/*
 	 * Do the actual freeing after releasing the mutex to avoid subtle
 	 * locking dependencies causing deadlocks.
+	 *
+	 * If there was an error in allocating @acomp_ctx->req, it
+	 * would be set to NULL.
 	 */
-	if (!IS_ERR_OR_NULL(req))
+	if (req)
 		acomp_request_free(req);
 	if (!IS_ERR_OR_NULL(acomp))
 		crypto_free_acomp(acomp);
-- 
2.39.5

On Mon, Mar 16, 2026 at 6:48 PM Kanchana P. Sridhar
<kanchanapsridhar2026@gmail.com> wrote:
>
> There are presently redundant checks on the per-CPU acomp_ctx and it's
> "req" member in zswap_cpu_comp_dead(): redundant because they are
> inconsistent with zswap_pool_create() handling of failure in allocating
> the acomp_ctx, and with the expected NULL return value from the
> acomp_request_alloc() API when it fails to allocate an acomp_req.
>
> Fix these by converting to them to be NULL checks.
>
> Add comments in zswap_cpu_comp_prepare() clarifying the expected return
> values of the crypto_alloc_acomp_node() and acomp_request_alloc() API.
>
> Suggested-by: Yosry Ahmed <yosry@kernel.org>
> Signed-off-by: Kanchana P. Sridhar <kanchanapsridhar2026@gmail.com>

Acked-by: Yosry Ahmed <yosry@kernel.org>

On Tue, Mar 17, 2026 at 12:19 PM Yosry Ahmed <yosry@kernel.org> wrote:
>
> On Mon, Mar 16, 2026 at 6:48 PM Kanchana P. Sridhar
> <kanchanapsridhar2026@gmail.com> wrote:
> >
> > There are presently redundant checks on the per-CPU acomp_ctx and it's
> > "req" member in zswap_cpu_comp_dead(): redundant because they are
> > inconsistent with zswap_pool_create() handling of failure in allocating
> > the acomp_ctx, and with the expected NULL return value from the
> > acomp_request_alloc() API when it fails to allocate an acomp_req.
> >
> > Fix these by converting to them to be NULL checks.
> >
> > Add comments in zswap_cpu_comp_prepare() clarifying the expected return
> > values of the crypto_alloc_acomp_node() and acomp_request_alloc() API.
> >
> > Suggested-by: Yosry Ahmed <yosry@kernel.org>
> > Signed-off-by: Kanchana P. Sridhar <kanchanapsridhar2026@gmail.com>
>
> Acked-by: Yosry Ahmed <yosry@kernel.org>

Thanks Yosry!