[v5.15] INFO: rcu detected stall in unix_stream_connect

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9eec9a14ee10 Linux 5.15.198
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1306c05a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=09f7db76df10783b57aa
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7146a7b4242e/disk-9eec9a14.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a11468b96c22/vmlinux-9eec9a14.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e7cb8f058e1c/bzImage-9eec9a14.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+09f7db...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 0-...!: (10564 ticks this GP) idle=1ab/1/0x4000000000000000 softirq=9768/9770 fqs=303
(t=10500 jiffies g=11869 q=280)
rcu: rcu_preempt kthread starved for 9890 jiffies! g11869 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
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:27760 pid: 15 ppid: 2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:1914
rcu_gp_fqs_loop+0x2be/0x11d0 kernel/rcu/tree.c:1972
rcu_gp_kthread+0x9b/0x370 kernel/rcu/tree.c:2145
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 1 skipped: idling at default_idle+0xb/0x10 arch/x86/kernel/process.c:729
NMI backtrace for cpu 0
CPU: 0 PID: 4946 Comm: syz.0.154 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<IRQ>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
rcu_dump_cpu_stacks+0x22f/0x380 kernel/rcu/tree_stall.h:349
print_cpu_stall+0x31d/0x5f0 kernel/rcu/tree_stall.h:633
check_cpu_stall kernel/rcu/tree_stall.h:727 [inline]
rcu_pending kernel/rcu/tree.c:3936 [inline]
rcu_sched_clock_irq+0x6ea/0x1120 kernel/rcu/tree.c:2619
update_process_times+0x193/0x200 kernel/time/timer.c:1818
tick_sched_handle kernel/time/tick-sched.c:254 [inline]
tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
__run_hrtimer kernel/time/hrtimer.c:1685 [inline]
__hrtimer_run_queues+0x4ad/0xb70 kernel/time/hrtimer.c:1749
hrtimer_interrupt+0x3bb/0x8d0 kernel/time/hrtimer.c:1811
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
__sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0x9b/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:deref_stack_reg+0xf5/0x120 arch/x86/kernel/unwind_orc.c:362
Code: e8 90 07 00 00 49 89 c6 48 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 47 f9 88 00 4c 89 33 b0 01 5b 41 5c 41 5d 41 5e <41> 5f 5d c3 44 89 f9 80 e1 07 80 c1 03 38 c1 0f 8c 5d ff ff ff 4c
RSP: 0018:ffffc90003e2f690 EFLAGS: 00000246
RAX: 1ffff920007c5e01 RBX: ffffc90003e2f768 RCX: 0000000000000001
RDX: ffffc90003e2f7a8 RSI: ffffc90003e2fb20 RDI: ffffc90003e2fb20
RBP: ffffc90003e30000 R08: ffffc90003e2f7c7 R09: ffffc90003e2f7b8
R10: dffffc0000000000 R11: fffff520007c5ef9 R12: 1ffffffff1c1c8b7
R13: dffffc0000000000 R14: ffffc90003e2f7b8 R15: ffffc90003e2f768
unwind_next_frame+0x115d/0x1d90 arch/x86/kernel/unwind_orc.c:-1
arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
kasan_slab_free include/linux/kasan.h:230 [inline]
slab_free_hook mm/slub.c:1710 [inline]
slab_free_freelist_hook+0xea/0x170 mm/slub.c:1736
slab_free mm/slub.c:3504 [inline]
kmem_cache_free+0x8f/0x210 mm/slub.c:3520
putname fs/namei.c:271 [inline]
kern_path+0x135/0x190 fs/namei.c:2592
unix_find_other+0xe9/0x840 net/unix/af_unix.c:1017
unix_stream_connect+0x39a/0xf90 net/unix/af_unix.c:1368
__sys_connect_file net/socket.c:1932 [inline]
__sys_connect+0x3cb/0x450 net/socket.c:1949
__do_sys_connect net/socket.c:1959 [inline]
__se_sys_connect net/socket.c:1956 [inline]
__x64_sys_connect+0x76/0x80 net/socket.c:1956
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: 0033:0x7f1df0696cb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1dee8f2028 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f1df0911fa0 RCX: 00007f1df0696cb9
RDX: 000000000000006e RSI: 0000200000000000 RDI: 0000000000000006
RBP: 00007f1df0704bf7 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1df0912038 R14: 00007f1df0911fa0 R15: 00007ffe78334128
</TASK>


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