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U2FsdGVkX19eXhaFx7jYQOgj1Ov1XXqJRSo+EatjSrybzLdSfdM9eWUnTE8OENix653GR8Vaofezyqid0+a5zVZ0NIOIz04J4ZfSN/9s8Ly0aHh9B5JbsEC9QqrKpoEbTUmRxAatRh1nCAXA43WSZXTqc+50Kd/CegOTG5u3lMSLKVkZxo+/k7G8L4T14aM7B5TaZRN/w5uqxVZiSHuxH9kVVNfiPjCRaXTaAjWz66ivveyYkf2xj69qwffDjXoVp4W0n5cXD/uu7/fjPBnXs9aVnEvlpQvKwyMJMqg1TbFhAxt/RQXGA5FWaAGlhls1UWVNgeFwDzyXrqnLgsJdhOA97MybDJfl5bl9CujuQOrUCg+u8JFibElih1DcRTj3jkwQbiIQbOkdyPWiGXWtTseDhK5j89vNKASKzaU3ebqHfopY3b8ecT3chRnPDd+ebfZ+HzXStMcyDAd5lAGXfY0EewSRFiZiXaxij7ciXolwbnfNf+dwIkjod6x9a7hyhSZfk6H4vAVSfkwrVxr78zB2vCmuloqTOiC3SxXjpFxP1VjnHkpeb4EaOI7vuuMfDb7SdpDAlM+VBBUM2oPrv5yjawysQtEXqn/aK8V05b54J3BTHoiHTZTUNeuzoDAr8UvHgz7mObHQDLTdMpIjbbyGw/Qk8yv5sSSHMh4guhtcBxws5Xo42pzOCP1jbvZwp6Rfdo7Llx7hatn3i4pY+etGis+y4NGqMHbC2UdNGLMHwvn4BI2+YC0IMYTqjWgXCqUWs2M+w5bvL0SaRXpxUInQ9lNDEbV4bOWiqsgStBbEWTOfhi6hYreH6ET2m/KyCnKpaYqq0q11iee/Z5MPd/0ZFA2MZ8oJzfFAaoMPeUZ1XOR9EB9oFppjF8NH9YAN8U4JbemNPD6vqWCIGyER4QjSm+DMjHNeZcsKk7m4VW7GUHbZoXNmGSoMJuZt6ZkUnHkDVfMecjEMBPiU0Ag ztDsKm7f 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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 ]--- Hi Hao, on which commit did you observe this warning? > This is due to a race condition that occurs when two threads concurrently > perform allocation and freeing operations on the same slab object. > > When a process is preparing to allocate a slab object, another process > successfully preempts the CPU, and then proceeds to free a slab object. > However, before the freeing process can invoke `alloc_tag_sub()`, it is > preempted again by the original allocating process. At this point, the > allocating process acquires the same slab object, and subsequently triggers > a warning when it invokes `alloc_tag_add()`. The explanation doesn't make sense to me, because alloc_tag_sub() should have been called before it's added back to freelist or sheaf before other threads can allocate it, or am I missing something? > Signed-off-by: Hao Ge > --- > mm/slub.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index f77b7407c51b..0d84fc917a89 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2261,8 +2261,13 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags) > * If other users appear then mem_alloc_profiling_enabled() > * check should be added before alloc_tag_add(). > */ > - if (likely(obj_exts)) > + if (likely(obj_exts)) { > + > + while (!READ_ONCE(obj_exts->ref.ct)) > + cpu_relax(); I don't think this is acceptable - it shouldn't wait forever even when there is a real bug that doesn't clear the tag. > + > alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size); > + } > else > alloc_tag_set_inaccurate(current->alloc_tag); > } > -- > 2.25.1 > -- Cheers, Harry / Hyeonggon