linux-kernel - Re: [linus:master] [slab] af92793e52: BUG_kmalloc-#(Not_tainted):Freepointer

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Message-ID: <692b6230-db0c-4369-85f0-539aa1c072bb@suse.cz>
Date: Mon, 13 Oct 2025 16:58:28 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: kernel test robot <oliver.sang@...el.com>,
 Alexei Starovoitov <ast@...nel.org>
Cc: oe-lkp@...ts.linux.dev, lkp@...el.com, linux-kernel@...r.kernel.org,
 Harry Yoo <harry.yoo@...cle.com>, kasan-dev@...glegroups.com,
 cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [linus:master] [slab] af92793e52:
 BUG_kmalloc-#(Not_tainted):Freepointer_corrupt

On 10/10/25 10:39, kernel test robot wrote:
> 
> 
> Hello,
> 
> kernel test robot noticed "BUG_kmalloc-#(Not_tainted):Freepointer_corrupt" on:
> 
> commit: af92793e52c3a99b828ed4bdd277fd3e11c18d08 ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> [test failed on      linus/master ec714e371f22f716a04e6ecb2a24988c92b26911]
> [test failed on linux-next/master 0b2f041c47acb45db82b4e847af6e17eb66cd32d]
> [test failed on        fix commit 83d59d81b20c09c256099d1c15d7da21969581bd]
> 
> in testcase: trinity
> version: trinity-i386-abe9de86-1_20230429
> with following parameters:
> 
> 	runtime: 300s
> 	group: group-01
> 	nr_groups: 5
> 
> 
> 
> config: i386-randconfig-012-20251004
> compiler: gcc-14
> test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> 
> (please refer to attached dmesg/kmsg for entire log/backtrace)
> 
> 
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <oliver.sang@...el.com>
> | Closes: https://lore.kernel.org/oe-lkp/202510101652.7921fdc6-lkp@intel.com

Does this fix it?
----8<----
>From 5f467c4e630a7a8e5ba024d31065413bddf22cec Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@...e.cz>
Date: Mon, 13 Oct 2025 16:56:28 +0200
Subject: [PATCH] slab: fix clearing freelist in free_deferred_objects()

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index f9f7f3942074..080d27fe253f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6377,15 +6377,16 @@ static void free_deferred_objects(struct irq_work *work)
 		slab = virt_to_slab(x);
 		s = slab->slab_cache;
 
+
+		/* Point 'x' back to the beginning of allocated object */
+		x -= s->offset;
 		/*
 		 * We used freepointer in 'x' to link 'x' into df->objects.
 		 * Clear it to NULL to avoid false positive detection
 		 * of "Freepointer corruption".
 		 */
-		*(void **)x = NULL;
+		set_freepointer(s, x, NULL);
 
-		/* Point 'x' back to the beginning of allocated object */
-		x -= s->offset;
 		__slab_free(s, slab, x, x, 1, _THIS_IP_);
 	}
 
-- 
2.51.0