[syzbot] [kernel?] possible deadlock in __schedule (2)

From: syzbot
Date: Fri Oct 20 2023 - 07:28:56 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 06dc10eae55b Merge tag 'fbdev-for-6.6-rc7' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13200f55680000
kernel config: https://syzkaller.appspot.com/x/.config?x=d236817624b4822c
dashboard link: https://syzkaller.appspot.com/bug?extid=39a85bc0224f82336405
compiler: aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-06dc10ea.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/84fbcc80ef2d/vmlinux-06dc10ea.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a061d48adac0/Image-06dc10ea.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+39a85bc0224f82336405@xxxxxxxxxxxxxxxxxxxxxxxxx

EEVDF scheduling fail, picking leftmost
======================================================
WARNING: possible circular locking dependency detected
6.6.0-rc6-syzkaller-00039-g06dc10eae55b #0 Not tainted
------------------------------------------------------
syz-executor.1/3112 is trying to acquire lock:
ffff8000865271b8 ((console_sem).lock){-.-.}-{2:2}, at: down_trylock+0x18/0x80 kernel/locking/semaphore.c:139

but task is already holding lock:
ffff00006a8dd758 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested kernel/sched/core.c:558 [inline]
ffff00006a8dd758 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock kernel/sched/sched.h:1372 [inline]
ffff00006a8dd758 (&rq->__lock){-.-.}-{2:2}, at: rq_lock kernel/sched/sched.h:1681 [inline]
ffff00006a8dd758 (&rq->__lock){-.-.}-{2:2}, at: __schedule+0x268/0x2ae4 kernel/sched/core.c:6612

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&rq->__lock){-.-.}-{2:2}:
_raw_spin_lock_nested+0x50/0x6c kernel/locking/spinlock.c:378
raw_spin_rq_lock_nested+0x2c/0x44 kernel/sched/core.c:558
raw_spin_rq_lock kernel/sched/sched.h:1372 [inline]
rq_lock kernel/sched/sched.h:1681 [inline]
task_fork_fair+0x70/0x13c kernel/sched/fair.c:12416
sched_cgroup_fork+0x35c/0x520 kernel/sched/core.c:4816
copy_process+0x2fb0/0x5520 kernel/fork.c:2609
kernel_clone+0x140/0x7e8 kernel/fork.c:2909
user_mode_thread+0xb4/0xf0 kernel/fork.c:2987
rest_init+0x2c/0x210 init/main.c:691
arch_post_acpi_subsys_init+0x0/0x8 init/main.c:823
start_kernel+0x328/0x3a0 init/main.c:1068
__primary_switched+0xb8/0xc0 arch/arm64/kernel/head.S:523

-> #1 (&p->pi_lock){-.-.}-{2:2}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x58/0x80 kernel/locking/spinlock.c:162
class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:518 [inline]
try_to_wake_up+0xac/0x1924 kernel/sched/core.c:4230
wake_up_process+0x18/0x24 kernel/sched/core.c:4478
__up.isra.0+0x124/0x18c kernel/locking/semaphore.c:278
up+0x94/0xd4 kernel/locking/semaphore.c:191
__up_console_sem kernel/printk/printk.c:346 [inline]
__console_unlock kernel/printk/printk.c:2718 [inline]
console_unlock+0x1b8/0x1d8 kernel/printk/printk.c:3037
fb_flashcursor drivers/video/fbdev/core/fbcon.c:382 [inline]
fb_flashcursor+0x220/0x340 drivers/video/fbdev/core/fbcon.c:348
process_one_work+0x670/0x143c kernel/workqueue.c:2630
process_scheduled_works kernel/workqueue.c:2703 [inline]
worker_thread+0x5a8/0xfb0 kernel/workqueue.c:2784
kthread+0x27c/0x300 kernel/kthread.c:388
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:857

-> #0 ((console_sem).lock){-.-.}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3868 [inline]
__lock_acquire+0x2cac/0x6b70 kernel/locking/lockdep.c:5136
lock_acquire kernel/locking/lockdep.c:5753 [inline]
lock_acquire+0x480/0x7c8 kernel/locking/lockdep.c:5718
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x58/0x80 kernel/locking/spinlock.c:162
down_trylock+0x18/0x80 kernel/locking/semaphore.c:139
__down_trylock_console_sem+0x38/0xd8 kernel/printk/printk.c:329
console_trylock kernel/printk/printk.c:2671 [inline]
console_trylock_spinning kernel/printk/printk.c:1927 [inline]
vprintk_emit+0x334/0x4e4 kernel/printk/printk.c:2306
vprintk_default+0x38/0x44 kernel/printk/printk.c:2322
vprintk+0x17c/0x1bc kernel/printk/printk_safe.c:45
_printk+0xa8/0xe0 kernel/printk/printk.c:2332
pick_eevdf kernel/sched/fair.c:976 [inline]
pick_next_entity kernel/sched/fair.c:5278 [inline]
pick_next_task_fair+0x1a4/0xd3c kernel/sched/fair.c:8222
__pick_next_task kernel/sched/core.c:6004 [inline]
pick_next_task kernel/sched/core.c:6514 [inline]
__schedule+0x3b8/0x2ae4 kernel/sched/core.c:6659
preempt_schedule_common kernel/sched/core.c:6864 [inline]
preempt_schedule+0xf4/0x254 kernel/sched/core.c:6888
__mutex_lock_common kernel/locking/mutex.c:613 [inline]
__mutex_lock+0x2b0/0x840 kernel/locking/mutex.c:747
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:799
xt_find_table_lock+0x68/0x418 net/netfilter/x_tables.c:1242
get_entries net/ipv6/netfilter/ip6_tables.c:1035 [inline]
do_ip6t_get_ctl+0x340/0x980 net/ipv6/netfilter/ip6_tables.c:1669
nf_getsockopt+0x78/0xec net/netfilter/nf_sockopt.c:116
ipv6_getsockopt+0x210/0x34c net/ipv6/ipv6_sockglue.c:1500
tcp_getsockopt+0x7c/0x248 net/ipv4/tcp.c:4278
sock_common_getsockopt+0x70/0xc8 net/core/sock.c:3672
__sys_getsockopt+0x190/0x478 net/socket.c:2371
__do_sys_getsockopt net/socket.c:2386 [inline]
__se_sys_getsockopt net/socket.c:2383 [inline]
__arm64_sys_getsockopt+0xa4/0x100 net/socket.c:2383
__invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
invoke_syscall+0x6c/0x258 arch/arm64/kernel/syscall.c:51
el0_svc_common.constprop.0+0xac/0x230 arch/arm64/kernel/syscall.c:136
do_el0_svc+0x40/0x58 arch/arm64/kernel/syscall.c:155
el0_svc+0x58/0x140 arch/arm64/kernel/entry-common.c:678
el0t_64_sync_handler+0x100/0x12c arch/arm64/kernel/entry-common.c:696
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:595

other info that might help us debug this:

Chain exists of:
(console_sem).lock --> &p->pi_lock --> &rq->__lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&rq->__lock);
lock(&p->pi_lock);
lock(&rq->__lock);
lock((console_sem).lock);

*** DEADLOCK ***

2 locks held by syz-executor.1/3112:
#0: ffff000013bfcd88 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x68/0x418 net/netfilter/x_tables.c:1242
#1: ffff00006a8dd758 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested kernel/sched/core.c:558 [inline]
#1: ffff00006a8dd758 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock kernel/sched/sched.h:1372 [inline]
#1: ffff00006a8dd758 (&rq->__lock){-.-.}-{2:2}, at: rq_lock kernel/sched/sched.h:1681 [inline]
#1: ffff00006a8dd758 (&rq->__lock){-.-.}-{2:2}, at: __schedule+0x268/0x2ae4 kernel/sched/core.c:6612

stack backtrace:
CPU: 0 PID: 3112 Comm: syz-executor.1 Not tainted 6.6.0-rc6-syzkaller-00039-g06dc10eae55b #0
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0x9c/0x11c arch/arm64/kernel/stacktrace.c:233
show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:240
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x74/0xd4 lib/dump_stack.c:106
dump_stack+0x1c/0x28 lib/dump_stack.c:113
print_circular_bug+0x420/0x6f8 kernel/locking/lockdep.c:2060
check_noncircular+0x2dc/0x364 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3868 [inline]
__lock_acquire+0x2cac/0x6b70 kernel/locking/lockdep.c:5136
lock_acquire kernel/locking/lockdep.c:5753 [inline]
lock_acquire+0x480/0x7c8 kernel/locking/lockdep.c:5718
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x58/0x80 kernel/locking/spinlock.c:162
down_trylock+0x18/0x80 kernel/locking/semaphore.c:139
__down_trylock_console_sem+0x38/0xd8 kernel/printk/printk.c:329
console_trylock kernel/printk/printk.c:2671 [inline]
console_trylock_spinning kernel/printk/printk.c:1927 [inline]
vprintk_emit+0x334/0x4e4 kernel/printk/printk.c:2306
vprintk_default+0x38/0x44 kernel/printk/printk.c:2322
vprintk+0x17c/0x1bc kernel/printk/printk_safe.c:45
_printk+0xa8/0xe0 kernel/printk/printk.c:2332
pick_eevdf kernel/sched/fair.c:976 [inline]
pick_next_entity kernel/sched/fair.c:5278 [inline]
pick_next_task_fair+0x1a4/0xd3c kernel/sched/fair.c:8222
__pick_next_task kernel/sched/core.c:6004 [inline]
pick_next_task kernel/sched/core.c:6514 [inline]
__schedule+0x3b8/0x2ae4 kernel/sched/core.c:6659
preempt_schedule_common kernel/sched/core.c:6864 [inline]
preempt_schedule+0xf4/0x254 kernel/sched/core.c:6888
__mutex_lock_common kernel/locking/mutex.c:613 [inline]
__mutex_lock+0x2b0/0x840 kernel/locking/mutex.c:747
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:799
xt_find_table_lock+0x68/0x418 net/netfilter/x_tables.c:1242
get_entries net/ipv6/netfilter/ip6_tables.c:1035 [inline]
do_ip6t_get_ctl+0x340/0x980 net/ipv6/netfilter/ip6_tables.c:1669
nf_getsockopt+0x78/0xec net/netfilter/nf_sockopt.c:116
ipv6_getsockopt+0x210/0x34c net/ipv6/ipv6_sockglue.c:1500
tcp_getsockopt+0x7c/0x248 net/ipv4/tcp.c:4278
sock_common_getsockopt+0x70/0xc8 net/core/sock.c:3672
__sys_getsockopt+0x190/0x478 net/socket.c:2371
__do_sys_getsockopt net/socket.c:2386 [inline]
__se_sys_getsockopt net/socket.c:2383 [inline]
__arm64_sys_getsockopt+0xa4/0x100 net/socket.c:2383
__invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
invoke_syscall+0x6c/0x258 arch/arm64/kernel/syscall.c:51
el0_svc_common.constprop.0+0xac/0x230 arch/arm64/kernel/syscall.c:136
do_el0_svc+0x40/0x58 arch/arm64/kernel/syscall.c:155
el0_svc+0x58/0x140 arch/arm64/kernel/entry-common.c:678
el0t_64_sync_handler+0x100/0x12c arch/arm64/kernel/entry-common.c:696
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:595

---
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Next message: Borislav Petkov: "Subject: [PATCH] x86/retpoline: Document some thunk handling aspects (was: Re: [PATCH 0/3] Ensure default return thunk isn't used at runtime)"
Previous message: Daniel Thompson: "Re: [PATCH] backlight: pwm_bl: Avoid backlight flicker applying initial PWM state"
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