Message-ID: <6890e4d6.050a0220.7f033.000e.GAE@google.com>
Date: Mon, 04 Aug 2025 09:50:30 -0700
From: syzbot <syzbot+c3740bc819eb55460ec3@...kaller.appspotmail.com>
To: andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org, 
	daniel@...earbox.net, eddyz87@...il.com, haoluo@...gle.com, 
	john.fastabend@...il.com, jolsa@...nel.org, kpsingh@...nel.org, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	martin.lau@...ux.dev, mathieu.desnoyers@...icios.com, 
	mattbobrowski@...gle.com, mhiramat@...nel.org, rostedt@...dmis.org, 
	sdf@...ichev.me, song@...nel.org, syzkaller-bugs@...glegroups.com, 
	yonghong.song@...ux.dev
Subject: [syzbot] [trace?] [bpf?] possible deadlock in down_trylock (3)

Hello,

syzbot found the following issue on:

HEAD commit:    84b92a499e7e Add linux-next specific files for 20250731
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11065aa2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b335f01a07f73eac
dashboard link: https://syzkaller.appspot.com/bug?extid=c3740bc819eb55460ec3
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14167834580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16f27cf0580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/97d9ce461c85/disk-84b92a49.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0ca812ed76e7/vmlinux-84b92a49.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0959d28a047f/bzImage-84b92a49.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c3740bc819eb55460ec3@...kaller.appspotmail.com

FAULT_INJECTION: forcing a failure.
name fail_usercopy, interval 1, probability 0, space 0, times 0
============================================
WARNING: possible recursive locking detected
6.16.0-next-20250731-syzkaller #0 Not tainted
--------------------------------------------
syz.3.22/6137 is trying to acquire lock:
ffffffff8e12e278 ((console_sem).lock){-...}-{2:2}, at: down_trylock+0x20/0xb0 kernel/locking/semaphore.c:176

but task is already holding lock:
ffffffff8e12e278 ((console_sem).lock){-...}-{2:2}, at: down+0x39/0xd0 kernel/locking/semaphore.c:96

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock((console_sem).lock);
  lock((console_sem).lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz.3.22/6137:
 #0: ffffffff8e12e278 ((console_sem).lock){-...}-{2:2}, at: down+0x39/0xd0 kernel/locking/semaphore.c:96
 #1: ffffffff8e139f20 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #1: ffffffff8e139f20 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #1: ffffffff8e139f20 (rcu_read_lock){....}-{1:3}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2256 [inline]
 #1: ffffffff8e139f20 (rcu_read_lock){....}-{1:3}, at: bpf_trace_run2+0x186/0x4b0 kernel/trace/bpf_trace.c:2298

stack backtrace:
CPU: 0 UID: 0 PID: 6137 Comm: syz.3.22 Not tainted 6.16.0-next-20250731-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3895
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0xa7/0xf0 kernel/locking/spinlock.c:162
 down_trylock+0x20/0xb0 kernel/locking/semaphore.c:176
 __down_trylock_console_sem+0xd0/0x1e0 kernel/printk/printk.c:326
 console_trylock kernel/printk/printk.c:2868 [inline]
 console_trylock_spinning kernel/printk/printk.c:2009 [inline]
 vprintk_emit+0x320/0x7a0 kernel/printk/printk.c:2449
 _printk+0xcf/0x120 kernel/printk/printk.c:2475
 fail_dump lib/fault-inject.c:66 [inline]
 should_fail_ex+0x3f5/0x560 lib/fault-inject.c:174
 strncpy_from_user+0x36/0x290 lib/strncpy_from_user.c:118
 strncpy_from_user_nofault+0x72/0x150 mm/maccess.c:192
 bpf_trace_copy_string kernel/bpf/helpers.c:755 [inline]
 bpf_bprintf_prepare+0xbbc/0x13d0 kernel/bpf/helpers.c:976
 ____bpf_trace_printk kernel/trace/bpf_trace.c:373 [inline]
 bpf_trace_printk+0xdb/0x190 kernel/trace/bpf_trace.c:363
 bpf_prog_7c77c7e0f6645ad8+0x3e/0x44
 bpf_dispatcher_nop_func include/linux/bpf.h:1322 [inline]
 __bpf_prog_run include/linux/filter.h:718 [inline]
 bpf_prog_run include/linux/filter.h:725 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2257 [inline]
 bpf_trace_run2+0x284/0x4b0 kernel/trace/bpf_trace.c:2298
 __bpf_trace_contention_begin+0xdc/0x130 include/trace/events/lock.h:95
 __do_trace_contention_begin include/trace/events/lock.h:95 [inline]
 trace_contention_begin include/trace/events/lock.h:95 [inline]
 __down_common+0x5ad/0x6a0 kernel/locking/semaphore.c:292
 down+0x80/0xd0 kernel/locking/semaphore.c:100
 console_lock+0x145/0x1b0 kernel/printk/printk.c:2849
 do_fb_ioctl+0x509/0x750 drivers/video/fbdev/core/fb_chrdev.c:123
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:584
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f92c678eb69
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:00007ffda68c54f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f92c69b5fa0 RCX: 00007f92c678eb69
RDX: 0000200000000080 RSI: 0000000000004606 RDI: 0000000000000005
RBP: 00007ffda68c5550 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f92c69b5fa0 R14: 00007f92c69b5fa0 R15: 0000000000000003
 </TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@...glegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Powered by blists - more mailing lists