syzbot

ID	Workflow	Result	Correct	Bug	Created	Started	Finished	Revision	Error
a06f638f-473f-4422-872e-43e6977d16dc	assessment-kcsan		💥	KCSAN: data-race in pcpu_alloc_noprof / pcpu_block_update_hint_alloc	2026/01/09 14:28	2026/01/09 14:28	2026/01/09 14:32	9ee25c60da3366005e31dedd1574732f63338151	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/80515aeb7bb25953f6dbc12929e3ff21c4f13eb5" "bzImage" "compile_commands.json"]: exit status 2

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BUG: KCSAN: data-race in pcpu_alloc_noprof / pcpu_block_update_hint_alloc

read-write to 0xffffffff8841e6ac of 4 bytes by task 3190 on cpu 1:
 pcpu_update_empty_pages mm/percpu.c:602 [inline]
 pcpu_block_update_hint_alloc+0x5db/0x6a0 mm/percpu.c:923
 pcpu_alloc_area+0x488/0x4b0 mm/percpu.c:1258
 pcpu_alloc_noprof+0x4b3/0x10c0 mm/percpu.c:1834
 xt_percpu_counter_alloc+0x79/0x110 net/netfilter/x_tables.c:1931
 find_check_entry net/ipv6/netfilter/ip6_tables.c:545 [inline]
 translate_table+0x9b1/0x1040 net/ipv6/netfilter/ip6_tables.c:733
 do_replace net/ipv6/netfilter/ip6_tables.c:1154 [inline]
 do_ip6t_set_ctl+0x7cc/0x8c0 net/ipv6/netfilter/ip6_tables.c:1644
 nf_setsockopt+0x195/0x1b0 net/netfilter/nf_sockopt.c:101
 ipv6_setsockopt+0x126/0x140 net/ipv6/ipv6_sockglue.c:999
 tcp_setsockopt+0x93/0xb0 net/ipv4/tcp.c:3765
 sock_common_setsockopt+0x64/0x80 net/core/sock.c:3726
 do_sock_setsockopt net/socket.c:2312 [inline]
 __sys_setsockopt+0x1d8/0x250 net/socket.c:2335
 __do_sys_setsockopt net/socket.c:2344 [inline]
 __se_sys_setsockopt net/socket.c:2341 [inline]
 __x64_sys_setsockopt+0x66/0x80 net/socket.c:2341
 x64_sys_call+0x1183/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:55
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff8841e6ac of 4 bytes by task 3196 on cpu 0:
 pcpu_alloc_noprof+0x9a7/0x10c0 mm/percpu.c:1894
 mm_alloc_cid_noprof include/linux/mm_types.h:1172 [inline]
 mm_init+0x47f/0x6f0 kernel/fork.c:1301
 dup_mm kernel/fork.c:1685 [inline]
 copy_mm+0x11e/0x11d0 kernel/fork.c:1737
 copy_process+0xee1/0x1f90 kernel/fork.c:2390
 kernel_clone+0x16a/0x570 kernel/fork.c:2797
 __do_sys_clone kernel/fork.c:2940 [inline]
 __se_sys_clone kernel/fork.c:2924 [inline]
 __x64_sys_clone+0xe8/0x120 kernel/fork.c:2924
 x64_sys_call+0x23e7/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:57
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000c -> 0x0000000b

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 3196 Comm: syz-executor.4 Not tainted 6.10.0-rc2-syzkaller-00315-gdc772f8237f9 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
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