[syzbot] [serial?] possible deadlock in tty_buffer_flush (3)

From: syzbot
Date: Mon Sep 09 2024 - 00:46:32 EST

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Hello,

syzbot found the following issue on:

HEAD commit: c7fb1692dc01 Merge tag 'for-linus' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ba5f33980000
kernel config: https://syzkaller.appspot.com/x/.config?x=8524e833fed2d47b
dashboard link: https://syzkaller.appspot.com/bug?extid=52cf91760dcb1dac6376
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: i386

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-c7fb1692.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c786784c3a2b/vmlinux-c7fb1692.xz
kernel image: https://storage.googleapis.com/syzbot-assets/21174af2f4f3/bzImage-c7fb1692.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+52cf91760dcb1dac6376@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
6.11.0-rc6-syzkaller-00048-gc7fb1692dc01 #0 Not tainted
------------------------------------------------------
kworker/1:2/1884 is trying to acquire lock:
ffff88801acb10b8 (&buf->lock){+.+.}-{3:3}, at: tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229

but task is already holding lock:
ffffffff8dda7160 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x13/0x310 drivers/tty/vt/vt_ioctl.c:983

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (console_lock){+.+.}-{0:0}:
console_lock+0x7a/0xa0 kernel/printk/printk.c:2735
con_flush_chars+0x5e/0x80 drivers/tty/vt/vt.c:3503
n_tty_write+0xe27/0x1150 drivers/tty/n_tty.c:2405
iterate_tty_write drivers/tty/tty_io.c:1021 [inline]
file_tty_write.constprop.0+0x518/0x9b0 drivers/tty/tty_io.c:1096
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x6b6/0x1140 fs/read_write.c:590
ksys_write+0x12f/0x260 fs/read_write.c:643
do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
__do_fast_syscall_32+0x73/0x120 arch/x86/entry/common.c:386
do_fast_syscall_32+0x32/0x80 arch/x86/entry/common.c:411
entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #1 (&tty->termios_rwsem){++++}-{3:3}:
down_write+0x93/0x200 kernel/locking/rwsem.c:1579
tty_unthrottle+0x1f/0x110 drivers/tty/tty_ioctl.c:103
hci_uart_tty_receive+0x394/0x780 drivers/bluetooth/hci_ldisc.c:625
tty_ldisc_receive_buf+0x153/0x190 drivers/tty/tty_buffer.c:391
tty_port_default_receive_buf+0x70/0xb0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:445 [inline]
flush_to_ldisc+0x264/0x780 drivers/tty/tty_buffer.c:495
process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231
process_scheduled_works kernel/workqueue.c:3312 [inline]
worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389
kthread+0x2c1/0x3a0 kernel/kthread.c:389
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #0 (&buf->lock){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3133 [inline]
check_prevs_add kernel/locking/lockdep.c:3252 [inline]
validate_chain kernel/locking/lockdep.c:3868 [inline]
__lock_acquire+0x24ed/0x3cb0 kernel/locking/lockdep.c:5142
lock_acquire kernel/locking/lockdep.c:5759 [inline]
lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5724
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x175/0x9c0 kernel/locking/mutex.c:752
tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229
tty_ldisc_flush+0x64/0xe0 drivers/tty/tty_ldisc.c:388
__do_SAK+0x6a1/0x800 drivers/tty/tty_io.c:3038
vc_SAK+0x7f/0x310 drivers/tty/vt/vt_ioctl.c:993
process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231
process_scheduled_works kernel/workqueue.c:3312 [inline]
worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389
kthread+0x2c1/0x3a0 kernel/kthread.c:389
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

other info that might help us debug this:

Chain exists of:
&buf->lock --> &tty->termios_rwsem --> console_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(console_lock);
lock(&tty->termios_rwsem);
lock(console_lock);
lock(&buf->lock);

*** DEADLOCK ***

4 locks held by kworker/1:2/1884:
#0: ffff88801ac88948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x11f0/0x1ad0 kernel/workqueue.c:3206
#1: ffffc9000ca8fd80 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x8bb/0x1ad0 kernel/workqueue.c:3207
#2: ffffffff8dda7160 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x13/0x310 drivers/tty/vt/vt_ioctl.c:983
#3: ffff88801281e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline]
#3: ffff88801281e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x1c/0xe0 drivers/tty/tty_ldisc.c:386

stack backtrace:
CPU: 1 UID: 0 PID: 1884 Comm: kworker/1:2 Not tainted 6.11.0-rc6-syzkaller-00048-gc7fb1692dc01 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: events vc_SAK
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:93 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:119
check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2186
check_prev_add kernel/locking/lockdep.c:3133 [inline]
check_prevs_add kernel/locking/lockdep.c:3252 [inline]
validate_chain kernel/locking/lockdep.c:3868 [inline]
__lock_acquire+0x24ed/0x3cb0 kernel/locking/lockdep.c:5142
lock_acquire kernel/locking/lockdep.c:5759 [inline]
lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5724
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x175/0x9c0 kernel/locking/mutex.c:752
tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229
tty_ldisc_flush+0x64/0xe0 drivers/tty/tty_ldisc.c:388
__do_SAK+0x6a1/0x800 drivers/tty/tty_io.c:3038
vc_SAK+0x7f/0x310 drivers/tty/vt/vt_ioctl.c:993
process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231
process_scheduled_works kernel/workqueue.c:3312 [inline]
worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389
kthread+0x2c1/0x3a0 kernel/kthread.c:389
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>
tty tty1: SAK: killed process 11375 (syz.3.1667): by fd#10

---
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Next message: Linux regression tracking (Thorsten Leemhuis): "Re: Can we get a bootable 6.11-rc kernel?"
Previous message: Al Viro: "Re: Can we get a bootable 6.11-rc kernel?"
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