[v6.1] INFO: rcu detected stall in kernfs_fop_write_iter (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 50cbba13faa2 Linux 6.1.159
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=170fd792580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6a5cbd268406bf43
dashboard link: https://syzkaller.appspot.com/bug?extid=5df2496a43a2ddc49e28
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b43fb8fc9816/disk-50cbba13.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ba3d5dc8928b/vmlinux-50cbba13.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2b4e001b3742/bzImage-50cbba13.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5df249...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2676 jiffies s: 102813 root: 0x1/.
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 15810 Comm: syz.6.2610 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:__this_cpu_preempt_check+0x0/0x10 lib/smp_processor_id.c:65
Code: 48 89 da e8 e2 e3 f4 ff 48 8b 74 24 30 48 c7 c7 a0 f9 be 8a e8 d1 e3 f4 ff e8 ba 8b ff ff eb a8 e8 35 ea ff ff 0f 1f 44 00 00 <48> 89 fe 48 c7 c7 20 f9 be 8a e9 e1 fe ff ff 00 eb 1e 0f 1f 00 48
RSP: 0018:ffffc90000007658 EFLAGS: 00000046
RAX: 0000000000000046 RBX: ffff88802b74e41c RCX: 3badf656bd536300
RDX: 0000000000000000 RSI: ffffffff8abef900 RDI: ffffffff8a6c12e0
RBP: ffffc90000007770 R08: dffffc0000000000 R09: fffffbfff1bfe1c6
R10: fffffbfff1bfe1c6 R11: 1ffffffff1bfe1c5 R12: 0000000000120000
R13: dffffc0000000000 R14: ffff88802b74d940 R15: 1ffff92000000ed8
FS: 00007f5c774526c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000077160000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
lockdep_recursion_inc kernel/locking/lockdep.c:462 [inline]
lock_release+0x16f/0x910 kernel/locking/lockdep.c:5681
rcu_lock_release include/linux/rcupdate.h:355 [inline]
rcu_read_unlock include/linux/rcupdate.h:824 [inline]
trace_call_bpf+0x59b/0x680 kernel/trace/bpf_trace.c:137
perf_trace_run_bpf_submit+0x79/0x1c0 kernel/events/core.c:9997
perf_trace_preemptirq_template+0x287/0x330 include/trace/events/preemptirq.h:14
trace_irq_enable_rcuidle+0xd3/0x140 include/trace/events/preemptirq.h:40
trace_hardirqs_on+0x24/0x40 kernel/trace/trace_preemptirq.c:44
asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
RIP: 0010:rcu_read_unlock_special+0x84/0x500 kernel/rcu/tree_plugin.h:685
Code: f1 f1 f1 00 f2 f2 f2 4a 89 04 2b 66 42 c7 44 2b 09 f3 f3 42 c6 44 2b 0b f3 65 44 8b 35 fd 86 96 7e 41 f7 c6 00 00 f0 00 74 45 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 66 42 c7 44 2b
RSP: 0018:ffffc90000007aa0 EFLAGS: 00000206
RAX: 3badf656bd536300 RBX: 1ffff92000000f5c RCX: 3badf656bd536300
RDX: dffffc0000000000 RSI: ffffffff8a6c0600 RDI: ffffffff8abef920
RBP: ffffc90000007b90 R08: dffffc0000000000 R09: fffffbfff211904b
R10: fffffbfff211904b R11: 1ffffffff211904a R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8e3b900 R15: 0000000000000001
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
rcu_read_unlock include/linux/rcupdate.h:823 [inline]
ieee80211_iterate_active_interfaces_atomic+0x156/0x170 net/mac80211/util.c:826
mac80211_hwsim_beacon+0xb7/0x1b0 drivers/net/wireless/mac80211_hwsim.c:2147
__run_hrtimer kernel/time/hrtimer.c:1747 [inline]
__hrtimer_run_queues+0x554/0xd60 kernel/time/hrtimer.c:1811
hrtimer_run_softirq+0x183/0x2a0 kernel/time/hrtimer.c:1828
handle_softirqs+0x2a1/0x920 kernel/softirq.c:596
__do_softirq kernel/softirq.c:630 [inline]
invoke_softirq kernel/softirq.c:470 [inline]
__irq_exit_rcu+0x12f/0x220 kernel/softirq.c:679
irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1118
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa5/0x100 kernel/locking/spinlock.c:194
Code: 74 05 e8 6e be 6c f7 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 16 44 3d f7 65 8b 05 a7 f1 e7 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc90005ebf540 EFLAGS: 00000206
RAX: 3badf656bd536300 RBX: 0000000000000a02 RCX: 3badf656bd536300
RDX: dffffc0000000000 RSI: ffffffff8a6c0600 RDI: 0000000000000001
RBP: ffffc90005ebf5d0 R08: dffffc0000000000 R09: fffffbfff211904b
R10: fffffbfff211904b R11: 1ffffffff211904a R12: dffffc0000000000
R13: ffff888017441dc0 R14: ffffffff8ca1a408 R15: 1ffff92000bd7ea8
kasan_quarantine_reduce+0x13a/0x160 mm/kasan/quarantine.c:292
__kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:305
kasan_slab_alloc include/linux/kasan.h:201 [inline]
slab_post_alloc_hook+0x4b/0x480 mm/slab.h:737
slab_alloc_node mm/slub.c:3359 [inline]
__kmem_cache_alloc_node+0x140/0x260 mm/slub.c:3398
kmalloc_trace+0x26/0xe0 mm/slab_common.c:1026
kmalloc include/linux/slab.h:563 [inline]
kzalloc include/linux/slab.h:699 [inline]
find_css_set+0x9b6/0x1540 kernel/cgroup/cgroup.c:1248
cgroup_migrate_prepare_dst+0x12c/0x6f0 kernel/cgroup/cgroup.c:2845
cgroup_attach_task+0x524/0x840 kernel/cgroup/cgroup.c:2951
__cgroup1_procs_write+0x2e0/0x3e0 kernel/cgroup/cgroup-v1.c:522
cgroup_file_write+0x2f8/0x660 kernel/cgroup/cgroup.c:4100
kernfs_fop_write_iter+0x3b2/0x520 fs/kernfs/file.c:352
call_write_iter include/linux/fs.h:2265 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x44c/0x960 fs/read_write.c:584
ksys_write+0x143/0x240 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f5c7658f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5c77452038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f5c767e6090 RCX: 00007f5c7658f749
RDX: 0000000000000012 RSI: 00002000000001c0 RDI: 0000000000000009
RBP: 00007f5c76613f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5c767e6128 R14: 00007f5c767e6090 R15: 00007ffdedf98268
</TASK>


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