syzbot

ID	Workflow	Result	Correct	Bug	Created	Started	Finished	Revision	Error
f53d528f-c715-4405-9b42-1ff8540328ee	assessment-kcsan		💥	KCSAN: data-race in pcpu_alloc / pcpu_free_area (3)	2026/01/15 15:16	2026/01/15 15:16	2026/01/15 15:19	a9d6a79219801d2130df3b1a792c57f0e5428e9f	failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "128" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/build/d88208df82ea3695227e1160bbbd1cd66c317e1c" "bzImage" "compile_commands.json"]: exit status 2

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BUG: KCSAN: data-race in pcpu_alloc / pcpu_free_area

read-write to 0xffffffff86f8915c of 4 bytes by task 3083 on cpu 0:
 pcpu_update_empty_pages mm/percpu.c:602 [inline]
 pcpu_block_update_hint_free mm/percpu.c:1044 [inline]
 pcpu_free_area+0x4e2/0x570 mm/percpu.c:1302
 free_percpu+0x1c9/0xb20 mm/percpu.c:2274
 xt_percpu_counter_free+0x63/0x70 net/netfilter/x_tables.c:1950
 cleanup_entry+0x18a/0x1b0 net/ipv6/netfilter/ip6_tables.c:671
 __do_replace+0x473/0x580 net/ipv6/netfilter/ip6_tables.c:1099
 do_replace net/ipv6/netfilter/ip6_tables.c:1154 [inline]
 do_ip6t_set_ctl+0x14e4/0x17d0 net/ipv6/netfilter/ip6_tables.c:1636
 nf_setsockopt+0x18d/0x1b0 net/netfilter/nf_sockopt.c:101
 ipv6_setsockopt+0x11c/0x130 net/ipv6/ipv6_sockglue.c:1017
 tcp_setsockopt+0x90/0xa0 net/ipv4/tcp.c:3697
 sock_common_setsockopt+0x61/0x70 net/core/sock.c:3697
 __sys_setsockopt+0x1c9/0x230 net/socket.c:2263
 __do_sys_setsockopt net/socket.c:2274 [inline]
 __se_sys_setsockopt net/socket.c:2271 [inline]
 __x64_sys_setsockopt+0x66/0x80 net/socket.c:2271
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffffffff86f8915c of 4 bytes by task 3092 on cpu 1:
 pcpu_alloc+0xa59/0x1280 mm/percpu.c:1870
 __alloc_percpu_gfp+0x26/0x30 mm/percpu.c:1930
 __percpu_counter_init+0x47/0x130 lib/percpu_counter.c:162
 mm_init+0x57c/0x750 kernel/fork.c:1305
 dup_mm kernel/fork.c:1686 [inline]
 copy_mm+0x11c/0xff0 kernel/fork.c:1738
 copy_process+0x1008/0x2180 kernel/fork.c:2504
 kernel_clone+0x169/0x560 kernel/fork.c:2912
 __do_sys_clone kernel/fork.c:3055 [inline]
 __se_sys_clone kernel/fork.c:3039 [inline]
 __x64_sys_clone+0xe8/0x120 kernel/fork.c:3039
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00000005 -> 0x00000006

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3092 Comm: syz-executor.0 Not tainted 6.5.0-rc7-syzkaller-00104-g4f9e7fabf864 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
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