[v5.15] INFO: rcu detected stall in kthread (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 91d48252ad4b Linux 5.15.202
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13d0aada580000
kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=613be74beec5938635ef
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10b11e16580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/74e75dfcb812/disk-91d48252.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bfa72aab00f2/vmlinux-91d48252.xz
kernel image: https://storage.googleapis.com/syzbot-assets/47ea72d1c7dc/bzImage-91d48252.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+613be7...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P3562/1:b..l
(detected by 1, t=10502 jiffies, g=7561, q=219)
task:udevd state:R running task stack:24408 pid: 3562 ppid: 1 flags:0x00004002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6571
preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6596
preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
_raw_spin_unlock_irqrestore+0x10d/0x120 kernel/locking/spinlock.c:194
spin_unlock_irqrestore include/linux/spinlock.h:419 [inline]
__wake_up_common_lock kernel/sched/wait.c:140 [inline]
__wake_up_sync_key+0x128/0x190 kernel/sched/wait.c:205
sock_def_readable+0x136/0x250 net/core/sock.c:3101
__netlink_sendskb net/netlink/af_netlink.c:1264 [inline]
netlink_sendskb+0x97/0x130 net/netlink/af_netlink.c:1270
netlink_sendmsg+0x8ba/0xbe0 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:706 [inline]
__sock_sendmsg net/socket.c:718 [inline]
____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2445
___sys_sendmsg+0x236/0x2e0 net/socket.c:2499
__sys_sendmsg net/socket.c:2528 [inline]
__do_sys_sendmsg net/socket.c:2537 [inline]
__se_sys_sendmsg+0x1af/0x290 net/socket.c:2535
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: 0033:0x7fcfe11fc407
RSP: 002b:00007ffc83dba330 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fcfe110e880 RCX: 00007fcfe11fc407
RDX: 0000000000000000 RSI: 00007ffc83dba390 RDI: 0000000000000004
RBP: 000055c5fa074250 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000000000b3
R13: 000055c5fa0349e0 R14: 0000000000000000 R15: 0000000000000000
</TASK>
rcu: rcu_preempt kthread starved for 7175 jiffies! g7561 f0x0 RCU_GP_DOING_FQS(6) ->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:28016 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
preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6799
irqentry_exit+0x63/0x70 kernel/entry/common.c:432
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:rcu_gp_fqs_loop+0xef/0x11d0 kernel/rcu/tree.c:-1
Code: 48 89 4c 24 68 48 c7 c0 04 17 8a 8d 48 c1 e8 03 48 89 44 24 28 48 c7 c0 68 e4 89 8d 48 c1 e8 03 48 89 44 24 50 4c 89 6c 24 58 <48> 89 d8 48 c1 e8 03 80 3c 10 00 74 12 48 89 df e8 0c 53 58 00 48
RSP: 0018:ffffc90000d47ca0 EFLAGS: 00000246
RAX: 00000000ffffcff8 RBX: ffffffff8c322a40 RCX: 03eac2b0e0e14e00
RDX: dffffc0000000000 RSI: ffffffff8a2b3a20 RDI: ffffffff8a79f980
RBP: ffffc90000d47df0 R08: ffffffff8c322f03 R09: 1ffffffff18645e0
R10: dffffc0000000000 R11: fffffbfff18645e1 R12: 1ffff11027fc5801
R13: 1ffffffff1801e30 R14: ffff88813fe2c00c R15: 0000000000000000
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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4371 Comm: syz.1.27 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x60 kernel/kcov.c:202
Code: 66 2e 0f 1f 84 00 00 00 00 00 53 48 89 fb e8 17 00 00 00 48 8b 3d 90 c4 10 0c 48 89 de 5b e9 b7 41 44 00 00 00 cc cc 00 00 cc <48> 8b 04 24 65 48 8b 0d a4 4e 89 7e 65 8b 15 a5 4e 89 7e 81 e2 00
RSP: 0018:ffffc900032cff10 EFLAGS: 00000283
RAX: 0000000000000027 RBX: ffffc900032cff20 RCX: 5742731b40992200
RDX: dffffc0000000000 RSI: 0000000000000027 RDI: ffffc900032cff58
RBP: ffffc900032cff48 R08: ffffffff8d89e36f R09: 1ffffffff1b13c6d
R10: dffffc0000000000 R11: fffffbfff1b13c6e R12: 0000000000000000
R13: 0000000000000000 R14: ffffc900032cff58 R15: 0000000000000027
FS: 00007ff2f84586c0(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000058 CR3: 00000000233a7000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__ia32_sys_getpid+0x5/0x20 kernel/sys.c:944
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: 0033:0x7ff2f8df0517
Code: 8d 3d 04 8e 0b 00 e8 58 1d fa ff e8 a3 87 00 00 0f 1f 00 b8 68 00 00 00 0f 05 c3 0f 1f 84 00 00 00 00 00 b8 27 00 00 00 0f 05 <c3> 0f 1f 84 00 00 00 00 00 b8 6e 00 00 00 0f 05 c3 0f 1f 84 00 00
RSP: 002b:00007ff2f8457b08 EFLAGS: 00000202 ORIG_RAX: 0000000000000027
RAX: ffffffffffffffda RBX: 00007ff2f8457c70 RCX: 00007ff2f8df0517
RDX: 00007ff2f8457b40 RSI: 00007ff2f8457c70 RDI: 0000000000000021
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007ff2f9070038 R14: 00007ffdb4983dd0 R15: 00007ffdb4983eb8
</TASK>


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