syzbot


possible deadlock in tty_buffer_flush (3)

Status: upstream: reported C repro on 2024/09/09 04:46
Subsystems: serial
[Documentation on labels]
Reported-by: syzbot+52cf91760dcb1dac6376@syzkaller.appspotmail.com
First crash: 157d, last: 1d11h
Cause bisection: introduced by (bisect log) :
commit a3c06ae158dd6fa8336157c31d9234689d068d02
Author: Parav Pandit <parav@nvidia.com>
Date: Tue Jan 5 10:32:03 2021 +0000

  vdpa_sim_net: Add support for user supported devices

Crash: possible deadlock in tty_buffer_flush (log)
Repro: C syz .config
  
Discussions (4)
Title Replies (including bot) Last reply
[syzbot] [serial?] possible deadlock in tty_buffer_flush (3) 0 (4) 2025/01/20 06:18
[syzbot] Monthly serial report (Jan 2025) 0 (1) 2025/01/17 10:36
[syzbot] Monthly serial report (Nov 2024) 0 (1) 2024/11/18 10:38
[syzbot] Monthly serial report (Sep 2024) 0 (1) 2024/09/14 10:58
Similar bugs (2)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in tty_buffer_flush serial 1 1296d 1292d 0/28 auto-closed as invalid on 2021/11/21 00:33
upstream possible deadlock in tty_buffer_flush (2) serial 7 1166d 1166d 0/28 auto-closed as invalid on 2022/03/31 16:04
Last patch testing requests (2)
Created Duration User Patch Repo Result
2025/02/04 06:02 26m retest repro upstream report log
2025/02/04 06:02 20m retest repro upstream report log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.13.0-rc7-syzkaller-00189-g595523945be0 #0 Not tainted
------------------------------------------------------
kworker/1:4/5864 is trying to acquire lock:
ffff88801b0990b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:229

but task is already holding lock:
ffffffff8e1a9040 (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:2833
       con_flush_chars+0x5e/0x80 drivers/tty/vt/vt.c:3503
       __receive_buf drivers/tty/n_tty.c:1644 [inline]
       n_tty_receive_buf_common+0xa99/0x1980 drivers/tty/n_tty.c:1739
       tty_ldisc_receive_buf+0xa2/0x190 drivers/tty/tty_buffer.c:387
       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+0x9c5/0x1ba0 kernel/workqueue.c:3236
       process_scheduled_works kernel/workqueue.c:3317 [inline]
       worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
       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

-> #1 (&tty->termios_rwsem){++++}-{4:4}:
       down_read+0x9a/0x330 kernel/locking/rwsem.c:1524
       n_tty_receive_buf_common+0x85/0x1980 drivers/tty/n_tty.c:1702
       tty_ldisc_receive_buf+0xa2/0x190 drivers/tty/tty_buffer.c:387
       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+0x9c5/0x1ba0 kernel/workqueue.c:3236
       process_scheduled_works kernel/workqueue.c:3317 [inline]
       worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
       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){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3161 [inline]
       check_prevs_add kernel/locking/lockdep.c:3280 [inline]
       validate_chain kernel/locking/lockdep.c:3904 [inline]
       __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5226
       lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5849
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x19b/0xa60 kernel/locking/mutex.c:735
       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+0x9c5/0x1ba0 kernel/workqueue.c:3236
       process_scheduled_works kernel/workqueue.c:3317 [inline]
       worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
       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/1:4/5864:
 #0: ffff88801b078948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1293/0x1ba0 kernel/workqueue.c:3211
 #1: ffffc90004a9fd80 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x921/0x1ba0 kernel/workqueue.c:3212
 #2: ffffffff8e1a9040 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x13/0x310 drivers/tty/vt/vt_ioctl.c:983
 #3: ffff8880698950a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline]
 #3: ffff8880698950a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x1c/0xe0 drivers/tty/tty_ldisc.c:386

stack backtrace:
CPU: 1 UID: 0 PID: 5864 Comm: kworker/1:4 Not tainted 6.13.0-rc7-syzkaller-00189-g595523945be0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Workqueue: events vc_SAK
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x419/0x5d0 kernel/locking/lockdep.c:2074
 check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2206
 check_prev_add kernel/locking/lockdep.c:3161 [inline]
 check_prevs_add kernel/locking/lockdep.c:3280 [inline]
 validate_chain kernel/locking/lockdep.c:3904 [inline]
 __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5226
 lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5849
 __mutex_lock_common kernel/locking/mutex.c:585 [inline]
 __mutex_lock+0x19b/0xa60 kernel/locking/mutex.c:735
 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+0x9c5/0x1ba0 kernel/workqueue.c:3236
 process_scheduled_works kernel/workqueue.c:3317 [inline]
 worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
 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 5889 (syz-executor496): by fd#4
usb 2-1: USB disconnect, device number 3
usb 2-1: new high-speed USB device number 4 using dummy_hcd
usb 2-1: config 0 interface 0 altsetting 0 endpoint 0x81 has an invalid bInterval 0, changing to 7
usb 2-1: New USB device found, idVendor=0926, idProduct=3333, bcdDevice= 0.40
usb 2-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 2-1: config 0 descriptor??
keytouch 0003:0926:3333.000F: fixing up Keytouch IEC report descriptor
input: HID 0926:3333 as /devices/platform/dummy_hcd.1/usb2/2-1/2-1:0.0/0003:0926:3333.000F/input/input19
keytouch 0003:0926:3333.000F: input,hidraw2: USB HID v0.00 Keyboard [HID 0926:3333] on usb-dummy_hcd.1-1/input0

Crashes (43):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/01/18 19:11 upstream 595523945be0 f2cb035c .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/12/31 22:34 upstream ccb98ccef0e5 d3ccff63 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/02/08 10:24 upstream 8f6629c004b1 ef44b750 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root possible deadlock in tty_buffer_flush
2025/02/07 01:15 upstream bb066fe812d6 53657d1b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root possible deadlock in tty_buffer_flush
2025/01/21 04:57 upstream ffd294d346d1 6e87cfa2 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/20 07:49 upstream 9528d418de4d f2cb035c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/20 05:07 upstream 9528d418de4d f2cb035c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/19 19:10 upstream fda5e3f28400 f2cb035c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/18 13:32 upstream 595523945be0 f2cb035c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/18 11:14 upstream 595523945be0 f2cb035c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/18 11:12 upstream 595523945be0 f2cb035c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/18 11:05 upstream 595523945be0 f2cb035c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/17 23:28 upstream 9bffa1ad25b8 953d1c45 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/17 09:31 upstream ce69b4019001 f9e07a6e .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/16 17:19 upstream 619f0b6fad52 968edaf4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/16 14:01 upstream 619f0b6fad52 968edaf4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/16 08:06 upstream 619f0b6fad52 968edaf4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/14 03:29 upstream c45323b7560e b1f1cd88 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/13 19:00 upstream 5bc55a333a2f 6dbc6a9b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/13 11:31 upstream be548645527a 6dbc6a9b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/12 16:10 upstream b62cef9a5c67 6dbc6a9b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/12 00:16 upstream 77a903cd8e5a 6dbc6a9b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/10 17:59 upstream 2144da25584e 67d7ec0a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/09 13:01 upstream eea6e4b4dfb8 f3558dbf .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/08 13:50 upstream 09a0fa92e5b4 f3558dbf .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/07 22:32 upstream fbfd64d25c7a f3558dbf .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/06 05:50 upstream ab75170520d4 f3558dbf .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/05 19:16 upstream ab75170520d4 f3558dbf .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/05 04:59 upstream ab75170520d4 f3558dbf .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2025/01/04 06:29 upstream 63676eefb7a0 f3558dbf .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/12/31 15:42 upstream ccb98ccef0e5 d3ccff63 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/12/26 12:27 upstream 9b2ffa6148b1 444551c4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root possible deadlock in tty_buffer_flush
2024/12/25 18:47 upstream 9b2ffa6148b1 444551c4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/12/10 23:06 upstream 7cb1b4663150 cfc402b4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/12/08 16:32 upstream 7503345ac5f5 9ac0fdc6 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/12/02 00:39 upstream bcc8eda6d349 68914665 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/11/23 07:43 upstream 06afb0f36106 68da6d95 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/11/06 12:56 upstream 2e1b3cc9d7f7 3a465482 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/11/02 05:24 upstream 6c52d4da1c74 f00eed24 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/10/30 12:39 upstream c1e939a21eb1 66aeb999 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/10/29 15:56 upstream e42b1a9a2557 66aeb999 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tty_buffer_flush
2024/12/02 05:18 upstream f788b5ef1ca9 68914665 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in tty_buffer_flush
2024/09/05 04:37 upstream c7fb1692dc01 dfbe2ed4 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in tty_buffer_flush
* Struck through repros no longer work on HEAD.