[v6.6] INFO: rcu detected stall in syscall_exit_to_user_mode

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6282921b6825 Linux 6.6.94
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1192370c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=96da6b2210cda427
dashboard link: https://syzkaller.appspot.com/bug?extid=a26ae52b1947e76c2e06
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1477af0c580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=138c9182580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a3bf0d8e22b2/disk-6282921b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d1d442f782d0/vmlinux-6282921b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a8378f4b7e1b/bzImage-6282921b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a26ae5...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: (detected by 1, t=10502 jiffies, g=9941, q=38 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10503 (4294966684-4294956181), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10504 jiffies! g9941 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:26568 pid:17 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5381 [inline]
__schedule+0x14e2/0x4580 kernel/sched/core.c:6700
schedule+0xbd/0x170 kernel/sched/core.c:6774
schedule_timeout+0x160/0x280 kernel/time/timer.c:2167
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: 5825 Comm: syz-executor544 Not tainted 6.6.94-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:__lock_acquire+0x1bcd/0x7c80 kernel/locking/lockdep.c:5168
Code: 08 45 31 f6 49 b8 00 00 00 00 00 fc ff df 48 c7 84 24 20 01 00 00 0e 36 e0 45 48 8b 84 24 f0 00 00 00 42 c7 04 00 00 00 00 00 <4a> c7 44 00 0b 00 00 00 00 42 c7 44 00 17 00 00 00 00 42 c6 44 00
RSP: 0018:ffffc900000079c0 EFLAGS: 00000083
RAX: 1ffff92000000f5c RBX: ffff88807bf2e4d8 RCX: ffffffff81671100
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff90d85528
RBP: ffffc90000007c08 R08: dffffc0000000000 R09: 1ffffffff21b0aa5
R10: dffffc0000000000 R11: fffffbfff21b0aa6 R12: 35590c0ea7cde75a
R13: ffff88807bf2da00 R14: 0000000000000001 R15: ffff88807bf2e500
FS: 0000555564d683c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb4b191ff10 CR3: 000000002faaa000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
seqcount_lockdep_reader_access+0xca/0x1c0 include/linux/seqlock.h:102
ktime_get+0x35/0x280 kernel/time/timekeeping.c:846
clockevents_program_event+0xe6/0x310 kernel/time/clockevents.c:326
hrtimer_interrupt+0x5a1/0x9c0 kernel/time/hrtimer.c:1894
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:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x29/0x50 kernel/locking/spinlock.c:202
Code: 00 f3 0f 1e fa 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 9a a7 f7 f6 48 89 df e8 b2 79 f8 f6 e8 cd 25 1c f7 fb bf 01 00 00 00 <e8> f2 90 eb f6 65 8b 05 03 e7 93 75 85 c0 74 02 5b c3 e8 e0 c8 90
RSP: 0018:ffffc900048bfc98 EFLAGS: 00000282
RAX: 31aa24b0d9471d00 RBX: ffff88802c04ca00 RCX: 31aa24b0d9471d00
RDX: dffffc0000000000 RSI: ffffffff8aaab2c0 RDI: 0000000000000001
RBP: ffff88802c04ce98 R08: ffffffff8e49ab2f R09: 1ffffffff1c93565
R10: dffffc0000000000 R11: fffffbfff1c93566 R12: 1ffff110058099d3
R13: 0000000000000021 R14: dffffc0000000000 R15: 0000000000000000
spin_unlock_irq include/linux/spinlock.h:401 [inline]
get_signal+0x11f5/0x1400 kernel/signal.c:2905
arch_do_signal_or_restart+0x96/0x780 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb4b1908899
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 19 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc83739c58 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000003 RCX: 00007fb4b1908899
RDX: 000020000006b000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 00007fb4b18c8990 R09: 00007fb4b18c8990
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb4b196633c
R13: 00007fb4b1960106 R14: 00007ffc83739c90 R15: 0000000000000000
</TASK>
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.193 msecs


---
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[syzbot]

syzbot suspects this issue could be fixed by backporting the following commit:

commit 5f6bd380c7bdbe10f7b4e8ddcceed60ce0714c6d
git tree: upstream
Author: Peter Zijlstra <pet...@infradead.org>
Date: Mon May 27 12:06:55 2024 +0000

sched/rt: Remove default bandwidth control

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1484d0a2580000

kernel config: https://syzkaller.appspot.com/x/.config?x=96da6b2210cda427
dashboard link: https://syzkaller.appspot.com/bug?extid=a26ae52b1947e76c2e06

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1477af0c580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=138c9182580000

Please keep in mind that other backports might be required as well.

For information about bisection process see: https://goo.gl/tpsmEJ#bisection