syzbot


INFO: rcu detected stall in sys_rt_sigreturn

Status: upstream: reported syz repro on 2025/09/16 12:37
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+b0c669c304df2c205c64@syzkaller.appspotmail.com
First crash: 48d, last: 47d
Bug presence (2)
Date Name Commit Repro Result
2025/09/19 linux-6.1.y (ToT) 3db754f56897 syz [report] INFO: rcu detected stall in corrupted
2025/09/19 upstream (ToT) 097a6c336d00 syz Didn't crash
Similar bugs (2)
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 2 28d 80d 0/2 upstream: reported C repro on 2025/08/14 20:21
linux-5.15 INFO: rcu detected stall in sys_rt_sigreturn missing-backport origin:lts-only 1 C done 107 22h16m 581d 0/3 upstream: reported C repro on 2024/04/01 14:20
Fix bisection attempts (1)
Created Duration User Patch Repo Result
2025/10/18 05:23 12h15m fix candidate upstream error job log

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
	(detected by 1, t=10502 jiffies, g=10485, q=164 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10501 (4294960674-4294950173), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10502 jiffies! g10485 f0x2 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:27840 pid:16    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x10ec/0x40b0 kernel/sched/core.c:6561
 schedule+0xb9/0x180 kernel/sched/core.c:6637
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:1965
 rcu_gp_fqs_loop+0x2f2/0x1310 kernel/rcu/tree.c:1706
 rcu_gp_kthread+0x95/0x380 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: 4538 Comm: syz.4.21 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:check_preemption_disabled+0x6/0x110 lib/smp_processor_id.c:13
Code: 89 f6 e8 dd 3e 17 fa e9 6e ff ff ff 00 00 cc cc 00 00 cc cc 48 c7 c7 40 fc de 8a 48 c7 c6 80 fc de 8a eb 00 55 41 57 41 56 53 <48> 83 ec 10 65 48 8b 04 25 28 00 00 00 48 89 44 24 08 65 8b 05 a1
RSP: 0018:ffffc90000007f80 EFLAGS: 00000083
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff81363ccb
RDX: 0000000000000000 RSI: ffffffff8adefc80 RDI: ffffffff8adefc40
RBP: 0000000000000000 R08: dffffc0000000000 R09: fffffbfff1c3eea6
R10: fffffbfff1c3eea6 R11: 1ffffffff1c3eea5 R12: dffffc0000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f4f5f2aa6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000058 CR3: 000000005cadb000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 rcu_dynticks_curr_cpu_in_eqs include/linux/context_tracking.h:122 [inline]
 rcu_is_watching+0x11/0xa0 kernel/rcu/tree.c:721
 trace_local_timer_exit arch/x86/include/asm/trace/irq_vectors.h:41 [inline]
 __sysvec_apic_timer_interrupt+0x1aa/0x5a0 arch/x86/kernel/apic/apic.c:1125
 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:memory_is_nonzero mm/kasan/generic.c:101 [inline]
RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:128 [inline]
RIP: 0010:memory_is_poisoned mm/kasan/generic.c:159 [inline]
RIP: 0010:check_region_inline mm/kasan/generic.c:180 [inline]
RIP: 0010:kasan_check_range+0x62/0x290 mm/kasan/generic.c:189
Code: ff df 49 89 fb 49 c1 eb 03 49 b8 00 00 00 00 00 fc ff df 4f 8d 0c 03 48 8d 5c 37 ff 48 c1 eb 03 4e 8d 14 3b 4d 89 d6 4d 29 ce <49> 83 fe 10 7f 26 4d 85 f6 0f 84 39 01 00 00 48 f7 d3 4c 01 db 41
RSP: 0018:ffffc90003887cb0 EFLAGS: 00000216
RAX: ffffffff84070701 RBX: 1ffff92000710fc3 RCX: ffffffff84070807
RDX: 0000000000000001 RSI: 00000000000000c0 RDI: ffffc90003887d60
RBP: 0000000000000000 R08: dffffc0000000000 R09: fffff52000710fac
R10: fffff52000710fc4 R11: 1ffff92000710fac R12: 00007fffffffef40
R13: 1ffff92000710ffe R14: 0000000000000018 R15: dffffc0000000001
 instrument_copy_from_user_before include/linux/instrumented.h:137 [inline]
 _copy_from_user+0xe7/0x170 lib/usercopy.c:22
 copy_from_user include/linux/uaccess.h:161 [inline]
 restore_sigcontext arch/x86/kernel/signal.c:92 [inline]
 __ia32_sys_rt_sigreturn+0x1e6/0x790 arch/x86/kernel/signal.c:675
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f4f5e32ada9
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:00007f4f5f2a9b40 EFLAGS: 00000206 ORIG_RAX: 000000000000000f
RAX: ffffffffffffffda RBX: 00007f4f5e5d5fa8 RCX: 00007f4f5e32ada9
RDX: 00007f4f5f2a9b40 RSI: 00007f4f5f2a9c70 RDI: 0000000000000021
RBP: 00007f4f5e5d5fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f4f5e5d6038 R14: 00007ffd7ffe4e20 R15: 00007ffd7ffe4f08
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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
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
* Struck through repros no longer work on HEAD.