WARNING in rcu_check_gp_start_stall (4)

Status: upstream: reported on 2026/02/20 21:56
Reported-by: syzbot+e952109dd720d190f944@syzkaller.appspotmail.com
First crash: 154d, last: 7d11h
Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING in rcu_check_gp_start_stall net prio:low -1 C done error 2949 2d13h 2709d 0/29 upstream: reported C repro on 2019/02/22 17:10
linux-5.15 WARNING in rcu_check_gp_start_stall (3) -1 6 260d 387d 0/3 auto-obsoleted due to no activity on 2026/02/15 02:49
linux-6.6 WARNING in rcu_check_gp_start_stall origin:lts-only -1 C done 148 7d23h 402d 0/2 upstream: reported C repro on 2025/06/17 13:49
linux-5.15 WARNING in rcu_check_gp_start_stall (2) -1 7 676d 821d 0/3 auto-obsoleted due to no activity on 2024/12/25 11:45
linux-5.15 WARNING in rcu_check_gp_start_stall -1 1 959d 959d 0/3 auto-obsoleted due to no activity on 2024/03/17 09:39
linux-6.1 WARNING in rcu_check_gp_start_stall origin:upstream missing-backport -1 C done 32 3d12h 1041d 0/3 upstream: reported C repro on 2023/09/17 20:24

Sample crash report:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at kernel/rcu/tree_stall.h:937 rcu_check_gp_start_stall+0x2dc/0x460 kernel/rcu/tree_stall.h:929
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
RIP: 0010:rcu_check_gp_start_stall+0x2dc/0x460 kernel/rcu/tree_stall.h:937
Code: ff ff ff 48 c7 c7 20 4c 33 96 be 04 00 00 00 e8 4a f6 58 00 48 89 df b8 01 00 00 00 87 05 9c 2f ce 14 85 c0 0f 85 19 ff ff ff <0f> 0b 48 81 ff 80 33 32 8c 74 47 48 c7 c0 84 1e 8b 8d 48 c1 e8 03
RSP: 0018:ffffc90000007bd8 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffffffff8c323380 RCX: ffffffff81651c76
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff8c323380
RBP: ffffc90000007e10 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff2c66984 R12: 0000000000002904
R13: dffffc0000000000 R14: 0000000000000a02 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0177f9e580 CR3: 00000000486a2000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 rcu_core+0x631/0x1650 kernel/rcu/tree.c:2758
 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:default_idle+0xb/0x10 arch/x86/kernel/process.c:730
Code: b7 48 89 df e8 56 a7 f5 f7 eb ad e8 3f ac f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 00 cc 66 90 0f 00 2d 57 64 5d 00 fb f4 <c3> 0f 1f 40 00 41 57 41 56 53 49 be 00 00 00 00 00 fc ff df 65 48
RSP: 0018:ffffffff8c007dc8 EFLAGS: 000002c6
RAX: 4ac790015fb92300 RBX: ffffffff8c0bc480 RCX: 4ac790015fb92300
RDX: 0000000000000001 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a2a40
RBP: ffffffff8c007ef8 R08: ffff8880b903b30b R09: 1ffff11017207661
R10: dffffc0000000000 R11: ffffed1017207662 R12: 1ffffffff1800fc4
R13: dffffc0000000000 R14: 1ffffffff1817890 R15: 0000000000000000
 default_idle_call+0x81/0xc0 kernel/sched/idle.c:112
 cpuidle_idle_call kernel/sched/idle.c:202 [inline]
 do_idle+0x3a1/0x650 kernel/sched/idle.c:326
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:424
 start_kernel+0x489/0x540 init/main.c:1153
 secondary_startup_64_no_verify+0xb1/0xbb
 </TASK>
----------------
Code disassembly (best guess):
   0:	b7 48                	mov    $0x48,%bh
   2:	89 df                	mov    %ebx,%edi
   4:	e8 56 a7 f5 f7       	call   0xf7f5a75f
   9:	eb ad                	jmp    0xffffffb8
   b:	e8 3f ac f6 ff       	call   0xfff6ac4f
  10:	00 00                	add    %al,(%rax)
  12:	cc                   	int3
  13:	cc                   	int3
  14:	00 00                	add    %al,(%rax)
  16:	cc                   	int3
  17:	cc                   	int3
  18:	00 00                	add    %al,(%rax)
  1a:	cc                   	int3
  1b:	cc                   	int3
  1c:	00 00                	add    %al,(%rax)
  1e:	cc                   	int3
  1f:	66 90                	xchg   %ax,%ax
  21:	0f 00 2d 57 64 5d 00 	verw   0x5d6457(%rip)        # 0x5d647f
  28:	fb                   	sti
  29:	f4                   	hlt
* 2a:	c3                   	ret <-- trapping instruction
  2b:	0f 1f 40 00          	nopl   0x0(%rax)
  2f:	41 57                	push   %r15
  31:	41 56                	push   %r14
  33:	53                   	push   %rbx
  34:	49 be 00 00 00 00 00 	movabs $0xdffffc0000000000,%r14
  3b:	fc ff df
  3e:	65                   	gs
  3f:	48                   	rex.W

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/17 19:56 linux-5.15.y c86c4726e7f0 8aaff637 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in rcu_check_gp_start_stall
2026/07/02 13:59 linux-5.15.y eceeec79dbc6 27192279 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf WARNING in rcu_check_gp_start_stall
2026/06/12 00:33 linux-5.15.y dc027a595035 d93a6ab6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in rcu_check_gp_start_stall
2026/05/23 03:44 linux-5.15.y 93741761e5e3 c69befb3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in rcu_check_gp_start_stall
2026/03/06 15:49 linux-5.15.y 91d48252ad4b 41d8037d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in rcu_check_gp_start_stall
2026/02/20 21:55 linux-5.15.y 3330a8d33e08 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan WARNING in rcu_check_gp_start_stall
* Struck through repros no longer work on HEAD.