Re: [PATCH v2] mm/slab: Add alloc_tagging_slab_free_hook for memcg_alloc_abort_single

[Vlastimil Babka <vbabka@suse.cz>]

On 2/4/26 13:00, Hao Li wrote:
> On Wed, Feb 04, 2026 at 06:14:01PM +0800, Hao Ge wrote:
>> When CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled, the following warning
>> may be noticed:
>> 
>> [ 3959.023862] ------------[ cut here ]------------
>> [ 3959.023891] alloc_tag was not cleared (got tag for lib/xarray.c:378)
>> [ 3959.023947] WARNING: ./include/linux/alloc_tag.h:155 at alloc_tag_add+0x128/0x178, CPU#6: mkfs.ntfs/113998
>> [ 3959.023978] Modules linked in: dns_resolver tun brd overlay exfat btrfs blake2b libblake2b xor xor_neon raid6_pq loop sctp ip6_udp_tunnel udp_tunnel ext4 crc16 mbcache jbd2 rfkill sunrpc vfat fat sg fuse nfnetlink sr_mod virtio_gpu cdrom drm_client_lib virtio_dma_buf drm_shmem_helper drm_kms_helper ghash_ce drm sm4 backlight virtio_net net_failover virtio_scsi failover virtio_console virtio_blk virtio_mmio dm_mirror dm_region_hash dm_log dm_multipath dm_mod i2c_dev aes_neon_bs aes_ce_blk [last unloaded: hwpoison_inject]
>> [ 3959.024170] CPU: 6 UID: 0 PID: 113998 Comm: mkfs.ntfs Kdump: loaded Tainted: G        W           6.19.0-rc7+ #7 PREEMPT(voluntary)
>> [ 3959.024182] Tainted: [W]=WARN
>> [ 3959.024186] Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
>> [ 3959.024192] pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>> [ 3959.024199] pc : alloc_tag_add+0x128/0x178
>> [ 3959.024207] lr : alloc_tag_add+0x128/0x178
>> [ 3959.024214] sp : ffff80008b696d60
>> [ 3959.024219] x29: ffff80008b696d60 x28: 0000000000000000 x27: 0000000000000240
>> [ 3959.024232] x26: 0000000000000000 x25: 0000000000000240 x24: ffff800085d17860
>> [ 3959.024245] x23: 0000000000402800 x22: ffff0000c0012dc0 x21: 00000000000002d0
>> [ 3959.024257] x20: ffff0000e6ef3318 x19: ffff800085ae0410 x18: 0000000000000000
>> [ 3959.024269] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
>> [ 3959.024281] x14: 0000000000000000 x13: 0000000000000001 x12: ffff600064101293
>> [ 3959.024292] x11: 1fffe00064101292 x10: ffff600064101292 x9 : dfff800000000000
>> [ 3959.024305] x8 : 00009fff9befed6e x7 : ffff000320809493 x6 : 0000000000000001
>> [ 3959.024316] x5 : ffff000320809490 x4 : ffff600064101293 x3 : ffff800080691838
>> [ 3959.024328] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0000d5bcd640
>> [ 3959.024340] Call trace:
>> [ 3959.024346]  alloc_tag_add+0x128/0x178 (P)
>> [ 3959.024355]  __alloc_tagging_slab_alloc_hook+0x11c/0x1a8
>> [ 3959.024362]  kmem_cache_alloc_lru_noprof+0x1b8/0x5e8
>> [ 3959.024369]  xas_alloc+0x304/0x4f0
>> [ 3959.024381]  xas_create+0x1e0/0x4a0
>> [ 3959.024388]  xas_store+0x68/0xda8
>> [ 3959.024395]  __filemap_add_folio+0x5b0/0xbd8
>> [ 3959.024409]  filemap_add_folio+0x16c/0x7e0
>> [ 3959.024416]  __filemap_get_folio_mpol+0x2dc/0x9e8
>> [ 3959.024424]  iomap_get_folio+0xfc/0x180
>> [ 3959.024435]  __iomap_get_folio+0x2f8/0x4b8
>> [ 3959.024441]  iomap_write_begin+0x198/0xc18
>> [ 3959.024448]  iomap_write_iter+0x2ec/0x8f8
>> [ 3959.024454]  iomap_file_buffered_write+0x19c/0x290
>> [ 3959.024461]  blkdev_write_iter+0x38c/0x978
>> [ 3959.024470]  vfs_write+0x4d4/0x928
>> [ 3959.024482]  ksys_write+0xfc/0x1f8
>> [ 3959.024489]  __arm64_sys_write+0x74/0xb0
>> [ 3959.024496]  invoke_syscall+0xd4/0x258
>> [ 3959.024507]  el0_svc_common.constprop.0+0xb4/0x240
>> [ 3959.024514]  do_el0_svc+0x48/0x68
>> [ 3959.024520]  el0_svc+0x40/0xf8
>> [ 3959.024526]  el0t_64_sync_handler+0xa0/0xe8
>> [ 3959.024533]  el0t_64_sync+0x1ac/0x1b0
>> [ 3959.024540] ---[ end trace 0000000000000000 ]---
>> 
>> When __memcg_slab_post_alloc_hook() fails, there are two different
>> free paths depending on whether size == 1 or size != 1. In the
>> kmem_cache_free_bulk() path, we do call alloc_tagging_slab_free_hook().
>> However, in memcg_alloc_abort_single() we don't, the above warning will be
>> triggered on the next allocation.
>> 
>> Therefore, add alloc_tagging_slab_free_hook() to the
>> memcg_alloc_abort_single() path.
>> 
>> Fixes: 9f9796b413d3 ("mm, slab: move memcg charging to post-alloc hook")
>> Suggested-by: Hao Li <hao.li@linux.dev>
>> Signed-off-by: Hao Ge <hao.ge@linux.dev>
>> ---
>> v2: Hao Li correctly pointed out the root cause of this problem.
>>     Per his suggestion, this patch adds the missing hook call.
>>     Many thanks to him for the thorough analysis.
>> ---
>>  mm/slub.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/mm/slub.c b/mm/slub.c
>> index f77b7407c51b..452a92544c6a 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -6689,6 +6689,8 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
>>  static noinline
>>  void memcg_alloc_abort_single(struct kmem_cache *s, void *object)
>>  {
>> +	alloc_tagging_slab_free_hook(s, virt_to_slab(object), &object, 1);
> 
> LGTM.
> 
> Minor nit: It would be cleaner to store the result of `virt_to_slab(object)` in a local
> variable and reuse it in the code that follows.

Did that locally, also added Cc: stable

> If you end up sending a v3, feel free to add:
> Reviewed-by: Hao Li <hao.li@linux.dev>

Pushed to slab/for-next-fixes, thanks!

> 
>> +
>>  	if (likely(slab_free_hook(s, object, slab_want_init_on_free(s), false)))
>>  		do_slab_free(s, virt_to_slab(object), object, object, 1, _RET_IP_);
>>  }
>> -- 
>> 2.25.1
>>