INFO: rcu detected stall in sys_rt_sigreturn

Status: upstream: reported C repro on 2025/08/14 20:21
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+334b9b0d2512a3d2f56a@syzkaller.appspotmail.com
First crash: 363d, last: 130d
Fix bisection: the issue occurs on the latest tested release (bisect log)
Crash: INFO: rcu detected stall in corrupted (log)
Repro: C syz .config
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/10/11 linux-6.6.y (ToT) e617101e5626 C [report] INFO: rcu detected stall in sys_newfstat
2025/10/11 upstream (ToT) 0739473694c4 C Didn't crash
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in sys_rt_sigreturn kernel 1 2 209d 241d 0/29 auto-obsoleted due to no activity on 2026/04/15 21:42
linux-6.1 INFO: rcu detected stall in sys_rt_sigreturn origin:lts-only 1 syz, C error 9 19d 330d 0/3 upstream: reported C repro on 2025/09/16 12:37
linux-5.15 INFO: rcu detected stall in sys_rt_sigreturn missing-backport origin:lts-only 1 syz, C done 190 11d 863d 0/3 upstream: reported C repro on 2024/04/01 14:20
▶ ▼ Fix bisection attempts (6)
Created Duration User Patch Repo Result
2026/05/22 07:29 18m fix candidate upstream error job log
2026/03/25 05:37 0m fix candidate upstream error job log
2026/02/21 12:43 1m fix candidate upstream error job log
2026/01/22 09:03 1m fix candidate upstream error job log
2026/01/16 14:21 2h27m bisect fix linux-6.6.y OK (0) job log log
2025/11/11 19:19 2h38m bisect fix linux-6.6.y OK (0) job log log

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P11/1:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=8781, q=342 ncpus=2)
task:kworker/u4:0    state:R  running task     stack:23984 pid:11    ppid:2      flags:0x00004000
Workqueue: ipv6_addrconf addrconf_dad_work
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 preempt_schedule_common+0x82/0xc0 kernel/sched/core.c:6866
 preempt_schedule+0xab/0xc0 kernel/sched/core.c:6890
 preempt_schedule_thunk+0x1a/0x30 arch/x86/entry/thunk_64.S:45
 unwind_next_frame+0x200f/0x2970 arch/x86/kernel/unwind_orc.c:672
 arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:383
 kmalloc include/linux/slab.h:600 [inline]
 dst_cow_metrics_generic+0x56/0x1c0 net/core/dst.c:195
 dst_metrics_write_ptr include/net/dst.h:133 [inline]
 dst_metric_set include/net/dst.h:194 [inline]
 icmp6_dst_alloc+0x22e/0x400 net/ipv6/route.c:3319
 ndisc_send_skb+0x419/0x14b0 net/ipv6/ndisc.c:493
 ndisc_send_ns+0xcc/0x150 net/ipv6/ndisc.c:671
 addrconf_dad_work+0xa25/0x14e0 net/ipv6/addrconf.c:4246
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: rcu_preempt kthread starved for 10536 jiffies! g8781 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:27752 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 schedule+0xbd/0x170 kernel/sched/core.c:6773
 schedule_timeout+0x160/0x280 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x302/0x1560 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x99/0x380 kernel/rcu/tree.c:1866
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </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: 5851 Comm: syz-executor246 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:class_preempt_destructor include/linux/preempt.h:478 [inline]
RIP: 0010:try_to_wake_up+0x71f/0x1140 kernel/sched/core.c:4355
Code: 8d 75 14 4c 89 f0 48 c1 e8 03 42 0f b6 04 38 84 c0 0f 85 91 00 00 00 45 8b 26 41 be 01 00 00 00 0f 1f 44 00 00 bf 01 00 00 00 <e8> ec 5a ff ff 65 8b 05 dd a1 a7 7e 85 c0 74 22 65 48 8b 04 25 28
RSP: 0018:ffffc90000007b98 EFLAGS: 00000046
RAX: 0000000000000000 RBX: 1ffff1100fd09783 RCX: ffffffff96e9b401
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000001
RBP: ffff88807e84bc00 R08: ffff88807e84bc07 R09: 1ffff1100fd09780
R10: dffffc0000000000 R11: ffffed100fd09781 R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: dffffc0000000000
FS:  00007fbf01cb76c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbf01cb6f80 CR3: 000000007703e000 CR4: 00000000003506f0
Call Trace:
 <IRQ>
 signal_wake_up_state kernel/signal.c:783 [inline]
 signal_wake_up include/linux/sched/signal.h:457 [inline]
 complete_signal+0x834/0xca0 kernel/signal.c:1076
 send_sigqueue+0x48d/0x710 kernel/signal.c:2034
 posix_timer_event kernel/time/posix-timers.c:299 [inline]
 posix_timer_fn+0x16e/0x3d0 kernel/time/posix-timers.c:325
 __run_hrtimer kernel/time/hrtimer.c:1750 [inline]
 __hrtimer_run_queues+0x51e/0xc40 kernel/time/hrtimer.c:1814
 hrtimer_interrupt+0x3c9/0x9c0 kernel/time/hrtimer.c:1876
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1077 [inline]
 __sysvec_apic_timer_interrupt+0xfb/0x3b0 arch/x86/kernel/apic/apic.c:1094
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0x9f/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:lock_acquire+0x1f2/0x410 kernel/locking/lockdep.c:5758
Code: 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 0f 85 f5 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 66 43 c7 44 3c 09 00 00 43 c6 44 3c 0b 00
RSP: 0018:ffffc90004c07b80 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 34827f53db2efe00
RDX: 0000000000000000 RSI: ffffffff8aaace60 RDI: ffffffff8afc6f80
RBP: ffffc90004c07c88 R08: dffffc0000000000 R09: 1ffffffff21b28a6
R10: dffffc0000000000 R11: fffffbfff21b28a7 R12: 1ffff92000980f7c
R13: ffff88807ee8ea20 R14: 0000000000000246 R15: dffffc0000000000
 __might_fault+0xc6/0x120 mm/memory.c:5968
 _copy_from_user+0x2a/0xe0 lib/usercopy.c:14
 copy_from_user include/linux/uaccess.h:183 [inline]
 restore_sigcontext arch/x86/kernel/signal_64.c:59 [inline]
 __ia32_sys_rt_sigreturn+0x27a/0x7b0 arch/x86/kernel/signal_64.c:266
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fbf01ccd869
Code: 64 c7 00 16 00 00 00 b8 ff ff ff ff c3 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 04 25
RSP: 002b:00007fbf01cb6bc0 EFLAGS: 00000202 ORIG_RAX: 000000000000000f
RAX: ffffffffffffffda RBX: 00007fbf01d8c1c8 RCX: 00007fbf01ccd869
RDX: 00007fbf01cb6bc0 RSI: 00007fbf01cb6cf0 RDI: 0000000000000021
RBP: 00007fbf01d8c1c0 R08: 00007fbf01cb76c0 R09: 0000000000000000
R10: 00007fbf01cb76c0 R11: 0000000000000202 R12: 00007fbf01d8c1cc
R13: 0000000000000016 R14: 00007fff32bf49c0 R15: 00007fff32bf4aa8
 </TASK>
sched: RT throttling activated

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/14 07:53 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in sys_rt_sigreturn
2025/10/06 05:40 linux-6.6.y f34f16e5c632 49379ee0 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in sys_rt_sigreturn
2026/04/04 09:46 linux-6.6.y c09fbcd31ae6 4440e7c2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in sys_rt_sigreturn
2025/08/14 20:20 linux-6.6.y 3a8ababb8b6a 5d8c2ac2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in sys_rt_sigreturn
* Struck through repros no longer work on HEAD.