The patch titled Subject: codetag: debug: handle existing CODETAG_EMPTY in mark_objexts_empty for slabobj_ext has been added to the -mm mm-hotfixes-unstable branch. Its filename is codetag-debug-handle-existing-codetag_empty-in-mark_objexts_empty-for-slabobj_ext.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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: Hao Ge gehao@kylinos.cn Subject: codetag: debug: handle existing CODETAG_EMPTY in mark_objexts_empty for slabobj_ext Date: Wed, 29 Oct 2025 09:43:17 +0800

When alloc_slab_obj_exts() fails and then later succeeds in allocating a slab extension vector, it calls handle_failed_objexts_alloc() to mark all objects in the vector as empty. As a result all objects in this slab (slabA) will have their extensions set to CODETAG_EMPTY.

Later on if this slabA is used to allocate a slabobj_ext vector for another slab (slabB), we end up with the slabB->obj_exts pointing to a slabobj_ext vector that itself has a non-NULL slabobj_ext equal to CODETAG_EMPTY. When slabB gets freed, free_slab_obj_exts() is called to free slabB->obj_exts vector.

free_slab_obj_exts() calls mark_objexts_empty(slabB->obj_exts) which will generate a warning because it expects slabobj_ext vectors to have a NULL obj_ext, not CODETAG_EMPTY.

Modify mark_objexts_empty() to skip the warning and setting the obj_ext value if it's already set to CODETAG_EMPTY.

To quickly detect this WARN, I modified the code from:WARN_ON(slab_exts[offs].ref.ct) to WARN_ON(slab_exts[offs].ref.ct == 1);

We then obtained this message:

[21630.898561] ------------[ cut here ]------------ [21630.898596] kernel BUG at mm/slub.c:2050! [21630.898611] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP [21630.900372] Modules linked in: squashfs isofs vfio_iommu_type1 vhost_vsock vfio vhost_net vmw_vsock_virtio_transport_common vhost tap vhost_iotlb iommufd vsock binfmt_misc nfsv3 nfs_acl nfs lockd grace netfs tls rds dns_resolver tun brd overlay ntfs3 exfat btrfs blake2b_generic xor xor_neon raid6_pq loop sctp ip6_udp_tunnel udp_tunnel nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables rfkill ip_set sunrpc vfat fat joydev sg sch_fq_codel nfnetlink virtio_gpu sr_mod cdrom drm_client_lib virtio_dma_buf drm_shmem_helper drm_kms_helper drm ghash_ce backlight virtio_net virtio_blk virtio_scsi net_failover virtio_console failover virtio_mmio dm_mirror dm_region_hash dm_log dm_multipath dm_mod fuse i2c_dev virtio_pci virtio_pci_legacy_dev virtio_pci_modern_dev virtio virtio_ring autofs4 aes_neon_bs aes_ce_blk [last unloaded: hwpoison_inject] [21630.909177] CPU: 3 UID: 0 PID: 3787 Comm: kylin-process-m Kdump: loaded Tainted: G�������������� W�������������������� 6.18.0-rc1+ #74 PREEMPT(voluntary) [21630.910495] Tainted: [W]=WARN [21630.910867] Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022 [21630.911625] pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [21630.912392] pc : __free_slab+0x228/0x250 [21630.912868] lr : __free_slab+0x18c/0x250[21630.913334] sp : ffff8000a02f73e0 [21630.913830] x29: ffff8000a02f73e0 x28: fffffdffc43fc800 x27: ffff0000c0011c40 [21630.914677] x26: ffff0000c000cac0 x25: ffff00010fe5e5f0 x24: ffff000102199b40 [21630.915469] x23: 0000000000000003 x22: 0000000000000003 x21: ffff0000c0011c40 [21630.916259] x20: fffffdffc4086600 x19: fffffdffc43fc800 x18: 0000000000000000 [21630.917048] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 [21630.917837] x14: 0000000000000000 x13: 0000000000000000 x12: ffff70001405ee66 [21630.918640] x11: 1ffff0001405ee65 x10: ffff70001405ee65 x9 : ffff800080a295dc [21630.919442] x8 : ffff8000a02f7330 x7 : 0000000000000000 x6 : 0000000000003000 [21630.920232] x5 : 0000000024924925 x4 : 0000000000000001 x3 : 0000000000000007 [21630.921021] x2 : 0000000000001b40 x1 : 000000000000001f x0 : 0000000000000001 [21630.921810] Call trace: [21630.922130]�� __free_slab+0x228/0x250 (P) [21630.922669]�� free_slab+0x38/0x118 [21630.923079]�� free_to_partial_list+0x1d4/0x340 [21630.923591]�� __slab_free+0x24c/0x348 [21630.924024]�� ___cache_free+0xf0/0x110 [21630.924468]�� qlist_free_all+0x78/0x130 [21630.924922]�� kasan_quarantine_reduce+0x114/0x148 [21630.925525]�� __kasan_slab_alloc+0x7c/0xb0 [21630.926006]�� kmem_cache_alloc_noprof+0x164/0x5c8 [21630.926699]�� __alloc_object+0x44/0x1f8 [21630.927153]�� __create_object+0x34/0xc8 [21630.927604]�� kmemleak_alloc+0xb8/0xd8 [21630.928052]�� kmem_cache_alloc_noprof+0x368/0x5c8 [21630.928606]�� getname_flags.part.0+0xa4/0x610 [21630.929112]�� getname_flags+0x80/0xd8 [21630.929557]�� vfs_fstatat+0xc8/0xe0 [21630.929975]�� __do_sys_newfstatat+0xa0/0x100 [21630.930469]�� __arm64_sys_newfstatat+0x90/0xd8 [21630.931046]�� invoke_syscall+0xd4/0x258 [21630.931685]�� el0_svc_common.constprop.0+0xb4/0x240 [21630.932467]�� do_el0_svc+0x48/0x68 [21630.932972]�� el0_svc+0x40/0xe0 [21630.933472]�� el0t_64_sync_handler+0xa0/0xe8 [21630.934151]�� el0t_64_sync+0x1ac/0x1b0 [21630.934923] Code: aa1803e0 97ffef2b a9446bf9 17ffff9c (d4210000) [21630.936461] SMP: stopping secondary CPUs [21630.939550] Starting crashdump kernel... [21630.940108] Bye!

Link: https://lkml.kernel.org/r/20251029014317.1533488-1-hao.ge@linux.dev Fixes: 09c46563ff6d ("codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations") Signed-off-by: Hao Ge gehao@kylinos.cn Cc: Christoph Lameter (Ampere) cl@gentwo.org Cc: David Rientjes rientjes@google.com Cc: gehao gehao@kylinos.cn Cc: Roman Gushchin roman.gushchin@linux.dev Cc: Shakeel Butt shakeel.butt@linux.dev Cc: Suren Baghdasaryan surenb@google.com Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/slub.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/mm/slub.c~codetag-debug-handle-existing-codetag_empty-in-mark_objexts_empty-for-slabobj_ext +++ a/mm/slub.c @@ -2046,7 +2046,11 @@ static inline void mark_objexts_empty(st if (slab_exts) { unsigned int offs = obj_to_index(obj_exts_slab->slab_cache, obj_exts_slab, obj_exts); - /* codetag should be NULL */ + + if (unlikely(is_codetag_empty(&slab_exts[offs].ref))) + return; + + /* codetag should be NULL here */ WARN_ON(slab_exts[offs].ref.ct); set_codetag_empty(&slab_exts[offs].ref); } _

Patches currently in -mm which might be from gehao@kylinos.cn are

codetag-debug-handle-existing-codetag_empty-in-mark_objexts_empty-for-slabobj_ext.patch