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WARNING: suspicious RCU usage in rhltable_lookup

Status: upstream: reported C repro on 2025/01/29 10:23
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+3b9b5f6a4cc6433864e0@syzkaller.appspotmail.com
First crash: 540d, last: 42m
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/03/16 linux-5.15.y (ToT) 0c935c049b5c C [report] WARNING: suspicious RCU usage in rhltable_lookup
2025/03/16 upstream (ToT) d1275e99d1c4 C Didn't crash
▶ ▼ Fix bisection attempts (5)
Created Duration User Patch Repo Result
2026/06/02 21:35 16m fix candidate upstream error job log
2026/04/09 13:48 1m fix candidate upstream error job log
2026/03/10 08:31 5m fix candidate upstream error job log
2026/02/07 16:39 1m fix candidate upstream error job log
2026/01/08 02:07 12h05m fix candidate upstream error job log

Sample crash report:
=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
include/linux/rhashtable.h:594 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz.0.17/4432:
 #0: ffffffff8d44b148 (rtnl_mutex){+.+.}-{3:3}, at: ip_mroute_setsockopt+0x139/0x1230 net/ipv4/ipmr.c:1362

stack backtrace:
CPU: 0 PID: 4432 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 __rhashtable_lookup include/linux/rhashtable.h:594 [inline]
 rhltable_lookup+0x787/0x7a0 include/linux/rhashtable.h:688
 mr_mfc_find_any_parent+0xb7/0x1d0 net/ipv4/ipmr_base.c:83
 ip_mr_forward+0x247/0xf60 net/ipv4/ipmr.c:1949
 ipmr_cache_resolve net/ipv4/ipmr.c:1003 [inline]
 ipmr_mfc_add+0x2273/0x2bd0 net/ipv4/ipmr.c:1262
 ip_mroute_setsockopt+0xecd/0x1230 net/ipv4/ipmr.c:1459
 do_ip_setsockopt net/ipv4/ip_sockglue.c:947 [inline]
 ip_setsockopt+0x568/0x31e0 net/ipv4/ip_sockglue.c:1430
 __sys_setsockopt+0x2bf/0x3d0 net/socket.c:2213
 __do_sys_setsockopt net/socket.c:2224 [inline]
 __se_sys_setsockopt net/socket.c:2221 [inline]
 __x64_sys_setsockopt+0xb1/0xc0 net/socket.c:2221
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fb84e88be59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd620c2e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007fb84eb13fa0 RCX: 00007fb84e88be59
RDX: 00000000000000d2 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007fb84e921e6f R08: 000000000000003c R09: 0000000000000000
R10: 0000200000000200 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb84eb13fac R14: 00007fb84eb13fa0 R15: 00007fb84eb13fa0
 </TASK>

=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
include/linux/rhashtable.h:369 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz.0.17/4432:
 #0: ffffffff8d44b148 (rtnl_mutex){+.+.}-{3:3}, at: ip_mroute_setsockopt+0x139/0x1230 net/ipv4/ipmr.c:1362

stack backtrace:
CPU: 1 PID: 4432 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 rht_ptr_rcu include/linux/rhashtable.h:369 [inline]
 __rhashtable_lookup include/linux/rhashtable.h:599 [inline]
 rhltable_lookup+0x512/0x7a0 include/linux/rhashtable.h:688
 mr_mfc_find_any_parent+0xb7/0x1d0 net/ipv4/ipmr_base.c:83
 ip_mr_forward+0x247/0xf60 net/ipv4/ipmr.c:1949
 ipmr_cache_resolve net/ipv4/ipmr.c:1003 [inline]
 ipmr_mfc_add+0x2273/0x2bd0 net/ipv4/ipmr.c:1262
 ip_mroute_setsockopt+0xecd/0x1230 net/ipv4/ipmr.c:1459
 do_ip_setsockopt net/ipv4/ip_sockglue.c:947 [inline]
 ip_setsockopt+0x568/0x31e0 net/ipv4/ip_sockglue.c:1430
 __sys_setsockopt+0x2bf/0x3d0 net/socket.c:2213
 __do_sys_setsockopt net/socket.c:2224 [inline]
 __se_sys_setsockopt net/socket.c:2221 [inline]
 __x64_sys_setsockopt+0xb1/0xc0 net/socket.c:2221
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fb84e88be59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd620c2e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007fb84eb13fa0 RCX: 00007fb84e88be59
RDX: 00000000000000d2 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007fb84e921e6f R08: 000000000000003c R09: 0000000000000000
R10: 0000200000000200 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb84eb13fac R14: 00007fb84eb13fa0 R15: 00007fb84eb13fa0
 </TASK>

=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
include/linux/rhashtable.h:614 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz.0.17/4432:
 #0: ffffffff8d44b148 (rtnl_mutex){+.+.}-{3:3}, at: ip_mroute_setsockopt+0x139/0x1230 net/ipv4/ipmr.c:1362

stack backtrace:
CPU: 1 PID: 4432 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 __rhashtable_lookup include/linux/rhashtable.h:614 [inline]
 rhltable_lookup+0x5fc/0x7a0 include/linux/rhashtable.h:688
 mr_mfc_find_any_parent+0xb7/0x1d0 net/ipv4/ipmr_base.c:83
 ip_mr_forward+0x247/0xf60 net/ipv4/ipmr.c:1949
 ipmr_cache_resolve net/ipv4/ipmr.c:1003 [inline]
 ipmr_mfc_add+0x2273/0x2bd0 net/ipv4/ipmr.c:1262
 ip_mroute_setsockopt+0xecd/0x1230 net/ipv4/ipmr.c:1459
 do_ip_setsockopt net/ipv4/ip_sockglue.c:947 [inline]
 ip_setsockopt+0x568/0x31e0 net/ipv4/ip_sockglue.c:1430
 __sys_setsockopt+0x2bf/0x3d0 net/socket.c:2213
 __do_sys_setsockopt net/socket.c:2224 [inline]
 __se_sys_setsockopt net/socket.c:2221 [inline]
 __x64_sys_setsockopt+0xb1/0xc0 net/socket.c:2221
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fb84e88be59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd620c2e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007fb84eb13fa0 RCX: 00007fb84e88be59
RDX: 00000000000000d2 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007fb84e921e6f R08: 000000000000003c R09: 0000000000000000
R10: 0000200000000200 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb84eb13fac R14: 00007fb84eb13fa0 R15: 00007fb84eb13fa0
 </TASK>

Crashes (9142):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/14 22:38 linux-5.15.y c86c4726e7f0 2130f682 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/04/05 21:14 linux-5.15.y 91d48252ad4b 4440e7c2 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2025/12/26 09:25 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2025/09/17 08:04 linux-5.15.y 43bb85222e53 e2beed91 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2025/06/09 05:44 linux-5.15.y 1c700860e8bc 4826c28e .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2025/03/01 04:38 linux-5.15.y c16c81c81336 67cf5345 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2025/01/29 11:05 linux-5.15.y 003148680b79 865ef71e .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 WARNING: suspicious RCU usage in rhltable_lookup
2026/07/23 11:42 linux-5.15.y c86c4726e7f0 881ce5c2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/23 10:09 linux-5.15.y c86c4726e7f0 881ce5c2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/23 08:22 linux-5.15.y c86c4726e7f0 881ce5c2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/22 22:34 linux-5.15.y c86c4726e7f0 4a865b71 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/22 09:48 linux-5.15.y c86c4726e7f0 b561ce9c .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/21 08:47 linux-5.15.y c86c4726e7f0 de6a700d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/21 00:08 linux-5.15.y c86c4726e7f0 de6a700d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/21 00:07 linux-5.15.y c86c4726e7f0 de6a700d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/20 22:16 linux-5.15.y c86c4726e7f0 de6a700d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/20 19:16 linux-5.15.y c86c4726e7f0 de6a700d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/20 04:49 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/20 02:17 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/20 01:11 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/20 01:08 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 23:26 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 22:18 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 18:39 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 17:24 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 10:19 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 09:07 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 07:08 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 05:37 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/19 05:32 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/18 19:53 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/18 18:08 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/18 10:30 linux-5.15.y c86c4726e7f0 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/18 02:52 linux-5.15.y c86c4726e7f0 8aaff637 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/17 14:19 linux-5.15.y c86c4726e7f0 7f27c57a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/17 12:12 linux-5.15.y c86c4726e7f0 7f27c57a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/17 11:12 linux-5.15.y c86c4726e7f0 7f27c57a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/17 11:11 linux-5.15.y c86c4726e7f0 7f27c57a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/17 01:53 linux-5.15.y c86c4726e7f0 71b49442 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/16 21:52 linux-5.15.y c86c4726e7f0 71b49442 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/16 19:22 linux-5.15.y c86c4726e7f0 71b49442 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/16 18:29 linux-5.15.y c86c4726e7f0 71b49442 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/16 10:20 linux-5.15.y c86c4726e7f0 27a8bd60 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/16 08:02 linux-5.15.y c86c4726e7f0 27a8bd60 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/16 06:42 linux-5.15.y c86c4726e7f0 27a8bd60 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/16 05:42 linux-5.15.y c86c4726e7f0 27a8bd60 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/15 16:46 linux-5.15.y c86c4726e7f0 a4ed0f4f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/15 14:34 linux-5.15.y c86c4726e7f0 a4ed0f4f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2026/07/15 14:25 linux-5.15.y c86c4726e7f0 a4ed0f4f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING: suspicious RCU usage in rhltable_lookup
2025/08/28 19:25 linux-5.15.y c79648372d02 e12e5ba4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 WARNING: suspicious RCU usage in rhltable_lookup
2025/01/29 10:22 linux-5.15.y 003148680b79 865ef71e .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 WARNING: suspicious RCU usage in rhltable_lookup
* Struck through repros no longer work on HEAD.