Re: [linus:master] [slab] af92793e52: BUG_kmalloc-#(Not_tainted):Freepointer_corrupt

[Oliver Sang <oliver.sang@intel.com>]

hi, Vlastimil Babka,

On Mon, Oct 13, 2025 at 04:58:28PM +0200, Vlastimil Babka wrote:
> 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@intel.com>
> > | Closes: https://lore.kernel.org/oe-lkp/202510101652.7921fdc6-lkp@intel.com
> 
> Does this fix it?

yes, this fixed the issue we reported. thanks

Tested-by: kernel test robot <oliver.sang@intel.com>

> ----8<----
> From 5f467c4e630a7a8e5ba024d31065413bddf22cec Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.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@suse.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
> 
>