INFO: rcu detected stall in sys_rt_sigreturn

Status: upstream: reported C repro on 2025/09/16 12:37
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+b0c669c304df2c205c64@syzkaller.appspotmail.com
First crash: 312d, last: 2d04h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/07/03 linux-6.1.y (ToT) fdb6fcb41cc7 C [report] INFO: rcu detected stall in corrupted
2026/07/03 upstream (ToT) d2c9a99135da C Didn't crash
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 INFO: rcu detected stall in sys_rt_sigreturn origin:lts-only 1 C error 4 113d 345d 0/2 upstream: reported C repro on 2025/08/14 20:21
upstream INFO: rcu detected stall in sys_rt_sigreturn kernel 1 2 191d 223d 0/29 auto-obsoleted due to no activity on 2026/04/15 21:42
linux-5.15 INFO: rcu detected stall in sys_rt_sigreturn missing-backport origin:lts-only 1 C done 189 1d02h 845d 0/3 upstream: reported C repro on 2024/04/01 14:20
▶ ▼ Fix bisection attempts (6)
Created Duration User Patch Repo Result
2026/06/08 08:57 13m fix candidate upstream error job log
2026/05/06 18:21 16m fix candidate upstream error job log
2026/03/29 01:07 1m fix candidate upstream error job log
2026/02/26 16:15 1m fix candidate upstream error job log
2026/01/24 05:12 2m fix candidate upstream error job log
2025/10/18 05:23 12h15m fix candidate upstream error job log

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P4390/1:b..l
	(detected by 1, t=10502 jiffies, g=12041, q=188 ncpus=2)
task:syz-executor    state:R  running task     stack:22096 pid:4390  ppid:4388   flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5245 [inline]
 __schedule+0x107f/0x4030 kernel/sched/core.c:6562
 preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6731
 preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6755
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 vprintk_emit+0x5e9/0x6a0 kernel/printk/printk.c:2304
 dev_vprintk_emit+0x32c/0x3de drivers/base/core.c:4948
 dev_printk_emit+0xeb/0x139 drivers/base/core.c:4959
 __netdev_printk+0x2ef/0x3d0 net/core/dev.c:11412
 netdev_info+0x11b/0x16c net/core/dev.c:11467
 nsim_udp_tunnel_set_port+0x28b/0x430 drivers/net/netdevsim/udp_tunnels.c:34
 udp_tunnel_nic_device_sync_one net/ipv4/udp_tunnel_nic.c:-1 [inline]
 udp_tunnel_nic_device_sync_by_port net/ipv4/udp_tunnel_nic.c:246 [inline]
 __udp_tunnel_nic_device_sync+0xa17/0x13c0 net/ipv4/udp_tunnel_nic.c:289
 udp_tunnel_nic_device_sync net/ipv4/udp_tunnel_nic.c:312 [inline]
 __udp_tunnel_nic_add_port+0xb81/0xe90 net/ipv4/udp_tunnel_nic.c:531
 udp_tunnel_nic_add_port include/net/udp_tunnel.h:348 [inline]
 udp_tunnel_notify_add_rx_port+0x290/0x3e0 net/ipv4/udp_tunnel_core.c:127
 geneve_socket_create drivers/net/geneve.c:619 [inline]
 geneve_sock_add+0x526/0x980 drivers/net/geneve.c:694
 geneve_open+0xcf/0x140 drivers/net/geneve.c:736
 __dev_open+0x2c7/0x430 net/core/dev.c:1501
 __dev_change_flags+0x1e4/0x6a0 net/core/dev.c:8676
 dev_change_flags+0x78/0x1a0 net/core/dev.c:8748
 do_setlink+0xbc7/0x29c0 net/core/rtnetlink.c:2837
 __rtnl_newlink net/core/rtnetlink.c:3614 [inline]
 rtnl_newlink+0x16e4/0x1f90 net/core/rtnetlink.c:3661
 rtnetlink_rcv_msg+0x863/0xfb0 net/core/rtnetlink.c:6158
 netlink_rcv_skb+0x1ef/0x440 net/netlink/af_netlink.c:2516
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x7ad/0x920 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x8ad/0xbd0 net/netlink/af_netlink.c:1877
 sock_sendmsg_nosec net/socket.c:718 [inline]
 __sock_sendmsg net/socket.c:730 [inline]
 __sys_sendto+0x497/0x650 net/socket.c:2153
 __do_sys_sendto net/socket.c:2165 [inline]
 __se_sys_sendto net/socket.c:2161 [inline]
 __x64_sys_sendto+0xda/0xf0 net/socket.c:2161
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f5ce415e6ce
RSP: 002b:00007ffc07e9d5b8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00005555665da500 RCX: 00007f5ce415e6ce
RDX: 000000000000002c RSI: 00007f5ce4f54670 RDI: 0000000000000003
RBP: 0000000000000001 R08: 00007ffc07e9d634 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000000 R14: 00007f5ce4f54670 R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 10559 jiffies! g12041 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:27888 pid:16    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5245 [inline]
 __schedule+0x107f/0x4030 kernel/sched/core.c:6562
 schedule+0xb9/0x180 kernel/sched/core.c:6638
 schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x303/0x1350 kernel/rcu/tree.c:1706
 rcu_gp_kthread+0x99/0x3b0 kernel/rcu/tree.c:1905
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4522 Comm: syz.2.30 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:mark_lock+0x3/0x320 kernel/locking/lockdep.c:4594
Code: 90 48 c7 c7 68 56 21 8e e8 6a 9a 6e 00 4c 89 f7 41 89 d9 e9 79 ff ff ff 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 41 57 <41> 56 41 55 41 54 53 50 89 d5 49 89 f6 48 89 fb 49 bd 00 00 00 00
RSP: 0018:ffffc900000079e8 EFLAGS: 00000006
RAX: 00000000000e404a RBX: ffff88802bc41e00 RCX: ffffffff8164adc4
RDX: 0000000000000008 RSI: ffff88802bc428e0 RDI: ffff88802bc41e00
RBP: ffffc90000007c30 R08: dffffc0000000000 R09: 1ffffffff2162049
R10: dffffc0000000000 R11: fffffbfff216204a R12: ffff88802bc428d8
R13: ffff88802bc41e00 R14: ffff88802bc428e0 R15: ffff88802bc42900
FS:  00007fd69a8126c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000058 CR3: 000000005a052000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 mark_usage kernel/locking/lockdep.c:4554 [inline]
 __lock_acquire+0xdf7/0x7c40 kernel/locking/lockdep.c:5017
 lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5676
 seqcount_lockdep_reader_access+0xcd/0x1d0 include/linux/seqlock.h:102
 ktime_get+0x31/0x270 kernel/time/timekeeping.c:846
 clockevents_program_event+0xe2/0x310 kernel/time/clockevents.c:326
 hrtimer_interrupt+0x561/0x980 kernel/time/hrtimer.c:1890
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1107 [inline]
 __sysvec_apic_timer_interrupt+0x153/0x5a0 arch/x86/kernel/apic/apic.c:1124
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
 sysvec_apic_timer_interrupt+0x9b/0xc0 arch/x86/kernel/apic/apic.c:1118
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: 00 00 00 66 90 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 de 0d 2a f7 48 89 df e8 66 d5 2a f7 e8 41 1f 4e f7 fb bf 01 00 00 00 <e8> c6 56 1e f7 65 8b 05 c7 07 c8 75 85 c0 74 02 5b c3 e8 d4 1b c6
RSP: 0018:ffffc90003577cd0 EFLAGS: 00000286
RAX: 28596aea8dac5400 RBX: ffff8880741e5c80 RCX: 28596aea8dac5400
RDX: dffffc0000000000 RSI: ffffffff8a8c17a0 RDI: 0000000000000001
RBP: ffffc90003577f10 R08: ffff8880741e5c83 R09: 1ffff1100e83cb90
R10: dffffc0000000000 R11: ffffed100e83cb91 R12: 1ffff920006aefa8
R13: dffffc0000000000 R14: 00007fd69a811b38 R15: ffff88802bc41e00
 __ia32_sys_rt_sigreturn+0x1ac/0x750 arch/x86/kernel/signal.c:673
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fd69993f219
Code: 11 06 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 90 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 c7 c0 0f 00 00 00 0f 05 <0f> 1f 80 00 00 00 00 48 81 ec 48 01 00 00 49 89 d0 64 48 8b 0c 25
RSP: 002b:00007fd69a811b40 EFLAGS: 00000206 ORIG_RAX: 000000000000000f
RAX: ffffffffffffffda RBX: 00007fd699c25fa8 RCX: 00007fd69993f219
RDX: 00007fd69a811b40 RSI: 00007fd69a811c70 RDI: 0000000000000021
RBP: 00007fd699c25fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007fd699c26038 R14: 00007ffc9656a790 R15: 00007ffc9656a878
 </TASK>

Crashes (9):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/18 23:40 linux-6.1.y 090666d3cc90 72524a66 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in sys_rt_sigreturn
2026/06/21 21:36 linux-6.1.y fdb6fcb41cc7 43bfcdb0 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in sys_rt_sigreturn
2026/06/21 01:07 linux-6.1.y fdb6fcb41cc7 43bfcdb0 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in sys_rt_sigreturn
2025/09/17 03:39 linux-6.1.y 3db754f56897 e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in sys_rt_sigreturn
2026/07/24 07:00 linux-6.1.y 090666d3cc90 544adce9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in sys_rt_sigreturn
2026/05/17 17:43 linux-6.1.y c27210688955 de5aae85 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in sys_rt_sigreturn
2026/01/14 14:18 linux-6.1.y bec0e10ee67e d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in sys_rt_sigreturn
2025/09/16 12:36 linux-6.1.y 3db754f56897 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in sys_rt_sigreturn
2026/07/11 07:32 linux-6.1.y 090666d3cc90 d78ea535 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 INFO: rcu detected stall in sys_rt_sigreturn
* Struck through repros no longer work on HEAD.