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BUG: KCSAN: data-race in __bpf_get_stackid / bcmp

write to 0xffff88812d2f27d8 of 248 bytes by task 5475 on cpu 1:
 __bpf_get_stackid+0x761/0x800 kernel/bpf/stackmap.c:288
 ____bpf_get_stackid kernel/bpf/stackmap.c:324 [inline]
 bpf_get_stackid+0xee/0x120 kernel/bpf/stackmap.c:300
 ____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1810 [inline]
 bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1799
 bpf_prog_e6fc920cfeff8120+0x2a/0x32
 bpf_dispatcher_nop_func include/linux/bpf.h:1332 [inline]
 __bpf_prog_run include/linux/filter.h:718 [inline]
 bpf_prog_run include/linux/filter.h:725 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2257 [inline]
 bpf_trace_run3+0x10c/0x1d0 kernel/trace/bpf_trace.c:2299
 __do_trace_kmem_cache_free include/trace/events/kmem.h:114 [inline]
 trace_kmem_cache_free include/trace/events/kmem.h:114 [inline]
 kmem_cache_free+0x257/0x300 mm/slub.c:4781
 skb_kfree_head net/core/skbuff.c:1045 [inline]
 skb_free_head+0x87/0x150 net/core/skbuff.c:1059
 skb_release_data+0x33b/0x370 net/core/skbuff.c:1086
 skb_release_all net/core/skbuff.c:1151 [inline]
 __kfree_skb+0x44/0x150 net/core/skbuff.c:1165
 consume_skb+0x49/0x150 net/core/skbuff.c:1397
 netlink_broadcast_filtered+0xb7b/0xc60 net/netlink/af_netlink.c:1537
 nlmsg_multicast_filtered include/net/netlink.h:1165 [inline]
 nlmsg_multicast include/net/netlink.h:1184 [inline]
 nlmsg_notify+0xcf/0x170 net/netlink/af_netlink.c:2595
 rtnl_notify+0x76/0x90 net/core/rtnetlink.c:958
 inet6_ifmcaddr_notify+0xd4/0x150 net/ipv6/mcast.c:928
 __ipv6_dev_mc_inc+0x4e4/0x5b0 net/ipv6/mcast.c:978
 ipv6_dev_mc_inc+0x1f/0x30 net/ipv6/mcast.c:986
 ipv6_add_dev+0x99c/0xb30 net/ipv6/addrconf.c:475
 addrconf_notify+0x4c8/0x930 net/ipv6/addrconf.c:3650
 notifier_call_chain kernel/notifier.c:85 [inline]
 raw_notifier_call_chain+0x6c/0x1b0 kernel/notifier.c:453
 call_netdevice_notifiers_info+0xae/0x100 net/core/dev.c:2229
 call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
 call_netdevice_notifiers net/core/dev.c:2281 [inline]
 register_netdevice+0xd48/0xf00 net/core/dev.c:11235
 register_netdev+0x3b/0x50 net/core/dev.c:11313
 loopback_net_init+0x59/0x100 drivers/net/loopback.c:218
 ops_init+0x22a/0x2e0 net/core/net_namespace.c:136
 setup_net+0x82/0x200 net/core/net_namespace.c:438
 copy_net_ns+0x266/0x390 net/core/net_namespace.c:570
 create_new_namespaces+0x20e/0x3d0 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0xe8/0x120 kernel/nsproxy.c:218
 ksys_unshare+0x3d0/0x6d0 kernel/fork.c:3127
 __do_sys_unshare kernel/fork.c:3198 [inline]
 __se_sys_unshare kernel/fork.c:3196 [inline]
 __x64_sys_unshare+0x1f/0x30 kernel/fork.c:3196
 x64_sys_call+0x2911/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:273
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88812d2f2800 of 8 bytes by task 31690 on cpu 0:
 memcmp lib/string.c:683 [inline]
 bcmp+0x23/0x90 lib/string.c:715
 memcmp include/linux/fortify-string.h:727 [inline]
 __bpf_get_stackid+0x371/0x800 kernel/bpf/stackmap.c:279
 ____bpf_get_stackid kernel/bpf/stackmap.c:324 [inline]
 bpf_get_stackid+0xee/0x120 kernel/bpf/stackmap.c:300
 ____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1810 [inline]
 bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1799
 bpf_prog_e6fc920cfeff8120+0x2a/0x32
 bpf_dispatcher_nop_func include/linux/bpf.h:1332 [inline]
 __bpf_prog_run include/linux/filter.h:718 [inline]
 bpf_prog_run include/linux/filter.h:725 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2257 [inline]
 bpf_trace_run3+0x10c/0x1d0 kernel/trace/bpf_trace.c:2299
 __do_trace_kmem_cache_free include/trace/events/kmem.h:114 [inline]
 trace_kmem_cache_free include/trace/events/kmem.h:114 [inline]
 kmem_cache_free+0x257/0x300 mm/slub.c:4781
 putname fs/namei.c:297 [inline]
 do_unlinkat+0x43e/0x480 fs/namei.c:4673
 __do_sys_unlink fs/namei.c:4696 [inline]
 __se_sys_unlink fs/namei.c:4694 [inline]
 __x64_sys_unlink+0x2e/0x40 fs/namei.c:4694
 x64_sys_call+0x2dc0/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:88
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffffffff81955d0e -> 0xffffffff844be0eb

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 31690 Comm: syz-executor Tainted: G        W           6.16.0-syzkaller-11952-g6e64f4580381 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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