linux-kernel - [syzbot] [udf?] INFO: rcu detected stall in call_usermodehelper_exec

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Message-ID: <6928665c.a70a0220.d98e3.0109.GAE@google.com>
Date: Thu, 27 Nov 2025 06:55:24 -0800
From: syzbot <syzbot+be81254ae29faa71cdfe@...kaller.appspotmail.com>
To: brauner@...nel.org, jack@...e.com, jack@...e.cz, kees@...nel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: [syzbot] [udf?] INFO: rcu detected stall in call_usermodehelper_exec_async
 (4)

Hello,

syzbot found the following issue on:

HEAD commit:    d724c6f85e80 Add linux-next specific files for 20251121
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16f1f742580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=68d11c703cf8e4a0
dashboard link: https://syzkaller.appspot.com/bug?extid=be81254ae29faa71cdfe
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12c3ea12580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1064d8b4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0ccfc806f65a/disk-d724c6f8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c2ec31ffb05e/vmlinux-d724c6f8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c25d9c0c1917/bzImage-d724c6f8.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/9174536af225/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+be81254ae29faa71cdfe@...kaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P6121/1:b..l
rcu: 	(detected by 1, t=10502 jiffies, g=13961, q=394 ncpus=2)
task:modprobe        state:R  running task     stack:26056 pid:6121  tgid:6121  ppid:13     task_flags:0x400000 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5257 [inline]
 __schedule+0x14bc/0x5030 kernel/sched/core.c:6864
 preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7191
 irqentry_exit+0x5d8/0x660 kernel/entry/common.c:216
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:unwind_next_frame+0xaa5/0x2390 arch/x86/kernel/unwind_orc.c:581
Code: 00 49 89 df 49 c1 ef 03 41 0f b6 04 2f 84 c0 0f 85 88 13 00 00 0f b6 76 01 83 e6 07 83 fe 04 4c 89 64 24 10 0f 84 49 04 00 00 <83> fe 03 0f 84 f3 01 00 00 83 fe 02 0f 85 a1 07 00 00 4c 89 7c 24
RSP: 0018:ffffc90003287898 EFLAGS: 00000293
RAX: 0000000000000000 RBX: ffffffff900ba31f RCX: ffffffff8f90e4cc
RDX: ffffffff900ba31a RSI: 0000000000000002 RDI: ffffffff8bbf8180
RBP: dffffc0000000000 R08: 0000000000000003 R09: ffffffff81745035
R10: ffffc900032879b8 R11: ffffffff81adcc20 R12: ffffc90003287f48
R13: ffffc900032879b8 R14: ffffc90003287968 R15: 1ffffffff2017463
 arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:252 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2540 [inline]
 slab_free mm/slub.c:6663 [inline]
 kfree+0x1c0/0x680 mm/slub.c:6871
 kernel_execve+0x3c7/0x9f0 fs/exec.c:1922
 call_usermodehelper_exec_async+0x210/0x360 kernel/umh.c:109
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
rcu: rcu_preempt kthread starved for 10537 jiffies! g13961 f0x0 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:27064 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5257 [inline]
 __schedule+0x14bc/0x5030 kernel/sched/core.c:6864
 __schedule_loop kernel/sched/core.c:6946 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6961
 schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </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 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:82
Code: cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 70 0c 00 f3 0f 1e fa fb f4 <e9> c8 f2 02 00 cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffffff8dc07d80 EFLAGS: 000002c6
RAX: 9d3ae734e5c61000 RBX: ffffffff8197acb7 RCX: 9d3ae734e5c61000
RDX: 0000000000000001 RSI: ffffffff8d78f71d RDI: ffffffff8bbf81e0
RBP: ffffffff8dc07ea8 R08: ffff8880b86336db R09: 1ffff110170c66db
R10: dffffc0000000000 R11: ffffed10170c66dc R12: ffffffff8f7deb70
R13: 0000000000000000 R14: 0000000000000000 R15: 1ffffffff1b92a60
FS:  0000000000000000(0000) GS:ffff888125eba000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc4b4703020 CR3: 000000002998e000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:767
 default_idle_call+0x73/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:190 [inline]
 do_idle+0x1e7/0x510 kernel/sched/idle.c:330
 cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:428
 rest_init+0x2de/0x300 init/main.c:757
 start_kernel+0x3a7/0x410 init/main.c:1206
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x147
 </TASK>


---
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