[syzbot] [bpf?] KCSAN: data-race in __htab_map_lookup_elem / bpf_lru_pop_free

[syzbot <syzbot+ad4661d6ca888ce7fe11@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    19272b37aa4f Linux 6.16-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=101f5a0c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f437300db311c188
dashboard link: https://syzkaller.appspot.com/bug?extid=ad4661d6ca888ce7fe11
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ab33a6ff9377/disk-19272b37.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d5cfaf818a35/vmlinux-19272b37.xz
kernel image: https://storage.googleapis.com/syzbot-assets/186f6b167a3a/bzImage-19272b37.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ad4661d6ca888ce7fe11@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __htab_map_lookup_elem / bpf_lru_pop_free

write to 0xffff8881042a62e8 of 4 bytes by task 22653 on cpu 0:
 __local_list_add_pending kernel/bpf/bpf_lru_list.c:358 [inline]
 bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:457 [inline]
 bpf_lru_pop_free+0xbd4/0xcb0 kernel/bpf/bpf_lru_list.c:504
 prealloc_lru_pop kernel/bpf/hashtab.c:303 [inline]
 __htab_lru_percpu_map_update_elem+0xea/0x600 kernel/bpf/hashtab.c:1349
 bpf_percpu_hash_update+0x61/0xa0 kernel/bpf/hashtab.c:2408
 bpf_map_update_value+0x297/0x3a0 kernel/bpf/syscall.c:266
 generic_map_update_batch+0x3f5/0x540 kernel/bpf/syscall.c:1982
 bpf_map_do_batch+0x255/0x380 kernel/bpf/syscall.c:5344
 __sys_bpf+0x2e0/0x790 kernel/bpf/syscall.c:-1
 __do_sys_bpf kernel/bpf/syscall.c:5943 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5941 [inline]
 __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:5941
 x64_sys_call+0x2478/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:322
 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 0xffff8881042a62e8 of 4 bytes by task 22637 on cpu 1:
 lookup_nulls_elem_raw kernel/bpf/hashtab.c:643 [inline]
 __htab_map_lookup_elem+0xab/0x150 kernel/bpf/hashtab.c:673
 htab_lru_percpu_map_lookup_elem+0x20/0xb0 kernel/bpf/hashtab.c:2342
 bpf_prog_1592a6279ab44e8a+0x48/0x50
 bpf_dispatcher_nop_func include/linux/bpf.h:1322 [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:2258 [inline]
 bpf_trace_run2+0x107/0x1c0 kernel/trace/bpf_trace.c:2299
 __traceiter_kfree+0x2e/0x50 include/trace/events/kmem.h:94
 __do_trace_kfree include/trace/events/kmem.h:94 [inline]
 trace_kfree include/trace/events/kmem.h:94 [inline]
 kfree+0x27b/0x320 mm/slub.c:4829
 ___sys_recvmsg+0x135/0x370 net/socket.c:2829
 do_recvmmsg+0x1ef/0x540 net/socket.c:2923
 __sys_recvmmsg net/socket.c:2997 [inline]
 __do_sys_recvmmsg net/socket.c:3020 [inline]
 __se_sys_recvmmsg net/socket.c:3013 [inline]
 __x64_sys_recvmmsg+0xe5/0x170 net/socket.c:3013
 x64_sys_call+0x1c6a/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:300
 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: 0x3dd8f34f -> 0x7cc9e3a7

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 22637 Comm: syz.3.6512 Tainted: G        W           6.16.0-rc1-syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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