Commit df90f6cd authored by Vlastimil Babka's avatar Vlastimil Babka
Browse files

slab: fix clearing freelist in free_deferred_objects() 



defer_free() links pending objects using the slab's freelist offset
which is fine as they are not free yet. free_deferred_objects() then
clears this pointer to avoid confusing the debugging consistency checks
that may be enabled for the cache.

However, with CONFIG_SLAB_FREELIST_HARDENED, even the NULL pointer needs
to be encoded appropriately using set_freepointer(), otherwise it's
decoded as something else and triggers the consistency checks, as found
by the kernel test robot.

Use set_freepointer() to prevent the issue.

Fixes: af92793e ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
Reported-and-tested-by: default avatarkernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202510101652.7921fdc6-lkp@intel.com


Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Reviewed-by: default avatarHarry Yoo <harry.yoo@oracle.com>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
parent 3a866087

mm/slub.c

+4 −3
Original line number Diff line number Diff line
@@ -6443,15 +6443,16 @@ 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_);

	}