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: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202510101652.7921fdc6-lkp@intel.com Acked-by: Alexei Starovoitov Signed-off-by: Vlastimil Babka --- will be added to slab/for-next-fixes and sent later this week --- mm/slub.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index b1f15598fbfd..64c17afc375b 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -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_); } --- base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787 change-id: 20251014-fix-freelist-29915edcc2f4 Best regards, -- Vlastimil Babka