+ mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: zswap: fix crypto_free_acomp deadlock in zswap_cpu_comp_dead
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Herbert Xu <herbert@gondor.apana.org.au>
Subject: mm: zswap: fix crypto_free_acomp deadlock in zswap_cpu_comp_dead
Date: Tue, 25 Feb 2025 16:53:58 +0800

Call crypto_free_acomp outside of the mutex in zswap_cpu_comp_dead() as
otherwise this could deadlock as the allocation path may lead back into
zswap while holding the same lock.  Zap the pointers to acomp and buffer
after freeing.

Also move the NULL check on acomp_ctx so that it takes place before
the mutex dereference.

Link: https://lkml.kernel.org/r/Z72FJnbA39zWh4zS@gondor.apana.org.au
Fixes: 12dcb0ef5406 ("mm: zswap: properly synchronize freeing resources during CPU hotunplug")
Reported-by: syzbot+1a517ccfcbc6a7ab0f82@syzkaller.appspotmail.com
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Cc: David S. Miller <davem@davemloft.net>
Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/zswap.c |   21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

--- a/mm/zswap.c~mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead
+++ a/mm/zswap.c
@@ -881,18 +881,23 @@ static int zswap_cpu_comp_dead(unsigned
 {
 	struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
 	struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
+	struct crypto_acomp *acomp = NULL;
+
+	if (IS_ERR_OR_NULL(acomp_ctx))
+		return 0;
 
 	mutex_lock(&acomp_ctx->mutex);
-	if (!IS_ERR_OR_NULL(acomp_ctx)) {
-		if (!IS_ERR_OR_NULL(acomp_ctx->req))
-			acomp_request_free(acomp_ctx->req);
-		acomp_ctx->req = NULL;
-		if (!IS_ERR_OR_NULL(acomp_ctx->acomp))
-			crypto_free_acomp(acomp_ctx->acomp);
-		kfree(acomp_ctx->buffer);
-	}
+	if (!IS_ERR_OR_NULL(acomp_ctx->req))
+		acomp_request_free(acomp_ctx->req);
+	acomp_ctx->req = NULL;
+	acomp = acomp_ctx->acomp;
+	acomp_ctx->acomp = NULL;
+	kfree(acomp_ctx->buffer);
+	acomp_ctx->buffer = NULL;
 	mutex_unlock(&acomp_ctx->mutex);
 
+	crypto_free_acomp(acomp);
+
 	return 0;
 }
 
_

Patches currently in -mm which might be from herbert@gondor.apana.org.au are

mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch