INFO: rcu detected stall in sys_wait4 (2)

Status: upstream: reported on 2026/04/29 19:33
Reported-by: syzbot+4837511a1b851eda355e@syzkaller.appspotmail.com
First crash: 110d, last: 43d
▶ ▼ Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in sys_wait4 (3) kernel 1 1 1088d 1088d 0/29 auto-obsoleted due to no activity on 2023/11/24 01:26
upstream INFO: rcu detected stall in sys_wait4 (2) kernel 1 1 1596d 1596d 0/29 auto-closed as invalid on 2022/07/03 11:21
upstream INFO: rcu detected stall in sys_wait4 (4) mm 1 syz, C done done 2 825d 858d 26/29 fixed on 2024/07/12 01:55
upstream INFO: rcu detected stall in sys_wait4 (7) prio:low fs 1 4 163d 244d 0/29 auto-obsoleted due to no activity on 2026/06/05 10:44
upstream INFO: rcu detected stall in sys_wait4 kernel 1 1 2227d 2227d 0/29 auto-closed as invalid on 2020/10/10 08:00
linux-5.15 INFO: rcu detected stall in sys_wait4 1 1 796d 796d 0/3 auto-obsoleted due to no activity on 2024/09/21 03:35
upstream INFO: rcu detected stall in sys_wait4 (5) kernel 1 1 599d 599d 0/29 auto-obsoleted due to no activity on 2025/03/26 13:51
linux-6.1 INFO: rcu detected stall in sys_wait4 1 1 1224d 1224d 0/3 auto-obsoleted due to no activity on 2023/08/09 13:38
upstream INFO: rcu detected stall in sys_wait4 (6) fs 1 2 407d 479d 0/29 auto-obsoleted due to no activity on 2025/10/04 12:51

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-....: (1 GPs behind) idle=591/1/0x4000000000000002 softirq=6918/6919 fqs=2100 
	(detected by 1, t=10505 jiffies, g=8109, q=2062)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4193 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:arch_static_branch arch/x86/include/asm/jump_label.h:27 [inline]
RIP: 0010:static_key_false include/linux/jump_label.h:212 [inline]
RIP: 0010:native_write_msr arch/x86/include/asm/msr.h:156 [inline]
RIP: 0010:wrmsr arch/x86/include/asm/msr.h:263 [inline]
RIP: 0010:native_apic_msr_write+0x35/0x50 arch/x86/include/asm/apic.h:208
Code: 74 2a 83 ff 30 74 25 eb 10 81 ff d0 00 00 00 74 1b 81 ff e0 00 00 00 74 13 c1 ef 04 81 c7 00 08 00 00 89 f9 89 f0 31 d2 0f 30 <66> 90 c3 89 f6 31 d2 e9 9f 8c d4 02 66 2e 0f 1f 84 00 00 00 00 00
RSP: 0018:ffffc90000006fc8 EFLAGS: 00000046
RAX: 00000000000000f6 RBX: ffffffff8be3aa20 RCX: 000000000000083f
RDX: 0000000000000000 RSI: 00000000000000f6 RDI: 000000000000083f
RBP: 0000000000000000 R08: ffff8880b9033d77 R09: 1ffff110172067ae
R10: dffffc0000000000 R11: ffffed10172067af R12: 0000000000000000
R13: dffffc0000000001 R14: dffffc0000000000 R15: 0000000000000000
FS:  0000555593588500(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555935884e8 CR3: 00000000635b9000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 arch_irq_work_raise+0x82/0xd0 arch/x86/kernel/irq_work.c:31
 irq_work_queue_on+0x11e/0x220 kernel/irq_work.c:109
 rcu_read_unlock_special+0x377/0x4a0 kernel/rcu/tree_plugin.h:667
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 __perf_event_output kernel/events/core.c:7813 [inline]
 perf_event_output_forward+0x255/0x2e0 kernel/events/core.c:7822
 __perf_event_overflow+0x35f/0x550 kernel/events/core.c:9515
 perf_tp_event+0x324/0xbe0 kernel/events/core.c:10047
 perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10021
 perf_trace_preemptirq_template+0x2aa/0x360 include/trace/events/preemptirq.h:14
 trace_irq_enable_rcuidle+0x108/0x180 include/trace/events/preemptirq.h:40
 trace_hardirqs_on+0x57/0x80 kernel/trace/trace_preemptirq.c:44
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x7f/0x4a0 kernel/rcu/tree_plugin.h:674
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 c2 22 9d 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc90000007780 EFLAGS: 00000206
RAX: 5660fec4a199bc00 RBX: 1ffff92000000ef4 RCX: 5660fec4a199bc00
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a2a40
RBP: ffffc90000007860 R08: ffffffff901e91c7 R09: 1ffffffff203d238
R10: dffffc0000000000 R11: fffffbfff203d239 R12: ffffffff8c323400
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 ndisc_send_skb+0xd39/0x1410 net/ipv6/ndisc.c:521
 addrconf_rs_timer+0x367/0x640 net/ipv6/addrconf.c:3959
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1699 [inline]
 __run_timers+0x56c/0x810 kernel/time/timer.c:1970
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
 handle_softirqs+0x336/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:call_rcu+0x697/0x900 kernel/rcu/tree.c:3092
Code: f7 84 24 a0 00 00 00 00 02 00 00 43 c6 44 25 04 f8 75 4f f7 44 24 58 00 02 00 00 74 01 fb 48 c7 84 24 80 00 00 00 0e 36 e0 45 <4b> c7 44 25 00 00 00 00 00 43 c7 44 25 08 00 00 00 00 65 48 8b 04
RSP: 0018:ffffc90002f5f3e0 EFLAGS: 00000206
RAX: 5660fec4a199bc00 RBX: ffff888060518ce0 RCX: 5660fec4a199bc00
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a2a40
RBP: ffffc90002f5f510 R08: ffff8880b903b30b R09: 1ffff11017207661
R10: dffffc0000000000 R11: ffffed1017207662 R12: dffffc0000000000
R13: 1ffff920005ebe8c R14: ffff8880b903b2d0 R15: 0000000000000008
 destroy_inode fs/inode.c:316 [inline]
 evict+0x810/0x8b0 fs/inode.c:662
 __dentry_kill+0x412/0x630 fs/dcache.c:586
 shrink_dentry_list+0x388/0x680 fs/dcache.c:1181
 shrink_dcache_parent+0xae/0x3d0 fs/dcache.c:-1
 d_invalidate+0x118/0x270 fs/dcache.c:1717
 proc_invalidate_siblings_dcache+0x396/0x650 fs/proc/inode.c:150
 release_task+0x147a/0x15f0 kernel/exit.c:269
 wait_task_zombie kernel/exit.c:1183 [inline]
 wait_consider_task+0x1932/0x2e30 kernel/exit.c:1410
 do_wait_thread kernel/exit.c:1473 [inline]
 do_wait+0x2f5/0xaa0 kernel/exit.c:1590
 kernel_wait4+0x22b/0x2b0 kernel/exit.c:1753
 __do_sys_wait4 kernel/exit.c:1781 [inline]
 __se_sys_wait4 kernel/exit.c:1777 [inline]
 __x64_sys_wait4+0x163/0x230 kernel/exit.c:1777
 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: 0033:0x7face292d68e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007ffcba8e9158 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
RAX: ffffffffffffffda RBX: 0000555593588500 RCX: 00007face292d68e
RDX: 0000000040000001 RSI: 00007ffcba8e91fc RDI: ffffffffffffffff
RBP: 00007ffcba8e91fc R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000001388
R13: 00000000000927c0 R14: 00000000000127cd R15: 00007ffcba8e9250
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/05 08:27 linux-5.15.y c86c4726e7f0 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in sys_wait4
2026/04/29 19:33 linux-5.15.y b9d57c40a767 7ca9e4d8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in sys_wait4
* Struck through repros no longer work on HEAD.