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KCSAN: data-race in __stop_tty / pty_write_room (8)

Status: moderation: reported on 2025/06/13 00:12
Subsystems: serial
[Documentation on labels]
Reported-by: syzbot+e29a46595d0cc68c2849@syzkaller.appspotmail.com
First crash: 4d00h, last: 4d00h
Similar bugs (7)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in __stop_tty / pty_write_room (2) serial 1 838d 838d 0/28 auto-obsoleted due to no activity on 2023/04/12 12:14
upstream KCSAN: data-race in __stop_tty / pty_write_room (5) serial 2 461d 465d 0/28 auto-obsoleted due to no activity on 2024/04/16 09:50
upstream KCSAN: data-race in __stop_tty / pty_write_room (3) serial 3 659d 668d 0/28 auto-obsoleted due to no activity on 2023/10/01 10:28
upstream KCSAN: data-race in __stop_tty / pty_write_room serial 1 1123d 1123d 0/28 auto-closed as invalid on 2022/06/24 17:06
upstream KCSAN: data-race in __stop_tty / pty_write_room (6) serial 11 278d 420d 0/28 auto-obsoleted due to no activity on 2024/10/16 04:41
upstream KCSAN: data-race in __stop_tty / pty_write_room (4) serial 2 509d 510d 0/28 auto-obsoleted due to no activity on 2024/02/28 07:28
upstream KCSAN: data-race in __stop_tty / pty_write_room (7) serial 6 68d 153d 0/28 auto-obsoleted due to no activity on 2025/06/04 23:18

Sample crash report:
==================================================================
BUG: KCSAN: data-race in __stop_tty / pty_write_room

write to 0xffff888119b86dbc of 1 bytes by task 6137 on cpu 0:
 __stop_tty+0x36/0x90 drivers/tty/tty_io.c:744
 n_tty_ioctl_helper+0x1e9/0x210 drivers/tty/tty_ioctl.c:951
 n_tty_ioctl+0x101/0x200 drivers/tty/n_tty.c:2509
 tty_ioctl+0x845/0xb80 drivers/tty/tty_io.c:2801
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:893
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893
 x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888119b86dbc of 1 bytes by task 31 on cpu 1:
 pty_write_room+0x19/0x70 drivers/tty/pty.c:131
 tty_write_room+0x3c/0x60 drivers/tty/tty_ioctl.c:69
 __process_echoes+0x36/0x6b0 drivers/tty/n_tty.c:687
 flush_echoes drivers/tty/n_tty.c:791 [inline]
 __receive_buf drivers/tty/n_tty.c:1626 [inline]
 n_tty_receive_buf_common+0x8e4/0xbe0 drivers/tty/n_tty.c:1723
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1769
 tty_ldisc_receive_buf+0x63/0xf0 drivers/tty/tty_buffer.c:387
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:445 [inline]
 flush_to_ldisc+0x144/0x360 drivers/tty/tty_buffer.c:495
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3321
 worker_thread+0x582/0x770 kernel/workqueue.c:3402
 kthread+0x486/0x510 kernel/kthread.c:464
 ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 31 Comm: kworker/u8:1 Not tainted 6.16.0-rc1-syzkaller-00101-g27605c8c0f69 #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: events_unbound flush_to_ldisc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/13 00:12 upstream 27605c8c0f69 98683f8f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __stop_tty / pty_write_room
* Struck through repros no longer work on HEAD.