[v5.15] INFO: rcu detected stall in sendfile64 (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c86c4726e7f0 Linux 5.15.211
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10d99d1c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6f8e2266b61925dc
dashboard link: https://syzkaller.appspot.com/bug?extid=f82981cd00f7429e4c9b
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c3e980557785/disk-c86c4726.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5fbaf3714ad0/vmlinux-c86c4726.xz
kernel image: https://storage.googleapis.com/syzbot-assets/de60a4f1e940/bzImage-c86c4726.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f82981...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 0-...!: (10500 ticks this GP) idle=425/1/0x4000000000000000 softirq=6218/6218 fqs=0
(t=10500 jiffies g=5913 q=63)
rcu: rcu_preempt kthread timer wakeup didn't happen for 10499 jiffies! g5913 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: Possible timer handling issue on cpu=0 timer-softirq=3671
rcu: rcu_preempt kthread starved for 10500 jiffies! g5913 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I stack:27872 pid: 15 ppid: 2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11c3/0x4350 kernel/sched/core.c:6395
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
rcu_gp_fqs_loop+0x2be/0x11f0 kernel/rcu/tree.c:1972
rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
kthread+0x42e/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:
NMI backtrace for cpu 0
CPU: 0 PID: 4324 Comm: syz.0.15 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487
print_cpu_stall+0x31a/0x5f0 kernel/rcu/tree_stall.h:631
check_cpu_stall kernel/rcu/tree_stall.h:727 [inline]
rcu_pending kernel/rcu/tree.c:3936 [inline]
rcu_sched_clock_irq+0x6ec/0x1120 kernel/rcu/tree.c:2619
update_process_times+0x193/0x200 kernel/time/timer.c:2021
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+0x4b0/0xb60 kernel/time/hrtimer.c:1749
hrtimer_interrupt+0x397/0x8b0 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:lock_acquire+0x208/0x400 kernel/locking/lockdep.c:5627
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3d 04 f8 0f 85 f1 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 43 c7 44 3d 08 00 00 00 00 65 48 8b 04
RSP: 0018:ffffc9000378f680 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: b30c91619edbf200
RDX: 0000000000000000 RSI: ffffffff8a2b3e80 RDI: ffffffff8a7a2a40
RBP: ffffc9000378f7a0 R08: dffffc0000000000 R09: 1ffffffff203d21a
R10: dffffc0000000000 R11: fffffbfff203d21b R12: ffffffff8c3ef360
R13: 1ffff920006f1edc R14: 0000000000000246 R15: dffffc0000000000
fs_reclaim_acquire+0x91/0x100 mm/page_alloc.c:4597
might_alloc include/linux/sched/mm.h:206 [inline]
slab_pre_alloc_hook+0x20/0xc0 mm/slab.h:492
slab_alloc_node mm/slub.c:3139 [inline]
slab_alloc mm/slub.c:3233 [inline]
__kmalloc+0x6b/0x340 mm/slub.c:4408
kmalloc_array include/linux/slab.h:647 [inline]
kcalloc include/linux/slab.h:676 [inline]
iter_file_splice_write+0x1a0/0xcf0 fs/splice.c:628
do_splice_from fs/splice.c:767 [inline]
direct_splice_actor+0xe1/0x130 fs/splice.c:956
splice_direct_to_actor+0x4e8/0xc00 fs/splice.c:902
do_splice_direct+0x1d4/0x2f0 fs/splice.c:1008
do_sendfile+0x524/0xe30 fs/read_write.c:1249
__do_sys_sendfile64 fs/read_write.c:1317 [inline]
__se_sys_sendfile64+0x141/0x1a0 fs/read_write.c:1303
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: 0033:0x7ff974a6ae59
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:00007ff972cc3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007ff974cf2fa0 RCX: 00007ff974a6ae59
RDX: 0000000000000000 RSI: 000000000000000a RDI: 000000000000000b
RBP: 00007ff974b00e6f R08: 0000000000000000 R09: 0000000000000000
R10: 000000007fffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff974cf3038 R14: 00007ff974cf2fa0 R15: 00007ffd546f40c8
</TASK>
NMI backtrace for cpu 0
CPU: 0 PID: 4324 Comm: syz.0.15 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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+0x22d/0x380 kernel/rcu/tree_stall.h:349
print_cpu_stall+0x31f/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+0x6ec/0x1120 kernel/rcu/tree.c:2619
update_process_times+0x193/0x200 kernel/time/timer.c:2021
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+0x4b0/0xb60 kernel/time/hrtimer.c:1749
hrtimer_interrupt+0x397/0x8b0 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:lock_acquire+0x208/0x400 kernel/locking/lockdep.c:5627
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3d 04 f8 0f 85 f1 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 43 c7 44 3d 08 00 00 00 00 65 48 8b 04
RSP: 0018:ffffc9000378f680 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: b30c91619edbf200
RDX: 0000000000000000 RSI: ffffffff8a2b3e80 RDI: ffffffff8a7a2a40
RBP: ffffc9000378f7a0 R08: dffffc0000000000 R09: 1ffffffff203d21a
R10: dffffc0000000000 R11: fffffbfff203d21b R12: ffffffff8c3ef360
R13: 1ffff920006f1edc R14: 0000000000000246 R15: dffffc0000000000
fs_reclaim_acquire+0x91/0x100 mm/page_alloc.c:4597
might_alloc include/linux/sched/mm.h:206 [inline]
slab_pre_alloc_hook+0x20/0xc0 mm/slab.h:492
slab_alloc_node mm/slub.c:3139 [inline]
slab_alloc mm/slub.c:3233 [inline]
__kmalloc+0x6b/0x340 mm/slub.c:4408
kmalloc_array include/linux/slab.h:647 [inline]
kcalloc include/linux/slab.h:676 [inline]
iter_file_splice_write+0x1a0/0xcf0 fs/splice.c:628
do_splice_from fs/splice.c:767 [inline]
direct_splice_actor+0xe1/0x130 fs/splice.c:956
splice_direct_to_actor+0x4e8/0xc00 fs/splice.c:902
do_splice_direct+0x1d4/0x2f0 fs/splice.c:1008
do_sendfile+0x524/0xe30 fs/read_write.c:1249
__do_sys_sendfile64 fs/read_write.c:1317 [inline]
__se_sys_sendfile64+0x141/0x1a0 fs/read_write.c:1303
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: 0033:0x7ff974a6ae59
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:00007ff972cc3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007ff974cf2fa0 RCX: 00007ff974a6ae59
RDX: 0000000000000000 RSI: 000000000000000a RDI: 000000000000000b
RBP: 00007ff974b00e6f R08: 0000000000000000 R09: 0000000000000000
R10: 000000007fffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff974cf3038 R14: 00007ff974cf2fa0 R15: 00007ffd546f40c8
</TASK>


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: c86c4726e7f0 Linux 5.15.211
git tree: linux-5.15.y

console output: https://syzkaller.appspot.com/x/log.txt?x=146286e0580000

kernel config: https://syzkaller.appspot.com/x/.config?x=6f8e2266b61925dc
dashboard link: https://syzkaller.appspot.com/bug?extid=f82981cd00f7429e4c9b
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16507719580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1503ef19580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c3e980557785/disk-c86c4726.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5fbaf3714ad0/vmlinux-c86c4726.xz
kernel image: https://storage.googleapis.com/syzbot-assets/de60a4f1e940/bzImage-c86c4726.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f82981...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
(detected by 0, t=10502 jiffies, g=7257, q=136)
rcu: All QSes seen, last rcu_preempt kthread activity 10502 (4294961221-4294950719), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10502 jiffies! g7257 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:27712 pid: 15 ppid: 2 flags:0x00004000

Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11c3/0x4350 kernel/sched/core.c:6395
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
rcu_gp_fqs_loop+0x2be/0x11f0 kernel/rcu/tree.c:1972
rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
kthread+0x42e/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:
NMI backtrace for cpu 0

CPU: 0 PID: 4384 Comm: syz.1.28 Not tainted syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487

print_other_cpu_stall+0x1110/0x1270 kernel/rcu/tree_stall.h:592
check_cpu_stall kernel/rcu/tree_stall.h:745 [inline]
rcu_pending kernel/rcu/tree.c:3936 [inline]
rcu_sched_clock_irq+0x845/0x1120 kernel/rcu/tree.c:2619

update_process_times+0x193/0x200 kernel/time/timer.c:2021
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+0x4b0/0xb60 kernel/time/hrtimer.c:1749
hrtimer_interrupt+0x397/0x8b0 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:__kasan_kmalloc+0x1/0xe0 mm/kasan/common.c:521
Code: e8 94 82 a9 ff 4c 89 ff 89 c6 44 89 f2 e8 57 d3 49 02 41 89 44 24 04 48 89 d8 48 8d 65 e0 5b 41 5c 41 5e 41 5f 5d c3 66 90 55 <48> 89 e5 41 57 41 56 41 54 53 48 83 e4 f0 48 81 ec 00 02 00 00 41
RSP: 0018:ffffc9000320f850 EFLAGS: 00000286
RAX: b932a891dec8e500 RBX: 0000000000000100 RCX: 0000000000000dc0
RDX: 0000000000000100 RSI: ffff888058187800 RDI: ffff888016c41b40
RBP: ffffc9000320fa50 R08: 0000000000000200 R09: ffff888058187800
R10: dffffc0000000000 R11: fffffbfff1b15d5e R12: dffffc0000000000
R13: ffff88807929cc00 R14: ffff888029f8ec80 R15: 1ffff92000641f24

kmalloc_array include/linux/slab.h:647 [inline]
kcalloc include/linux/slab.h:676 [inline]
iter_file_splice_write+0x1a0/0xcf0 fs/splice.c:628
do_splice_from fs/splice.c:767 [inline]
direct_splice_actor+0xe1/0x130 fs/splice.c:956
splice_direct_to_actor+0x4e8/0xc00 fs/splice.c:902
do_splice_direct+0x1d4/0x2f0 fs/splice.c:1008
do_sendfile+0x524/0xe30 fs/read_write.c:1249
__do_sys_sendfile64 fs/read_write.c:1317 [inline]
__se_sys_sendfile64+0x141/0x1a0 fs/read_write.c:1303
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: 0033:0x7ff9009d4e59

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:00007ffdb2639938 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007ff900c5cfa0 RCX: 00007ff9009d4e59
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000007
RBP: 00007ff900a6ae6f R08: 0000000000000000 R09: 0000000000000000

R10: 000000007fffffff R11: 0000000000000246 R12: 0000000000000000

R13: 00007ff900c5cfac R14: 00007ff900c5cfa0 R15: 00007ff900c5cfa0
</TASK>


---
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