[moderation] [serial?] KCSAN: data-race in n_tty_receive_char / n_tty_write (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cc8ed4d0a848 Merge tag 'drm-fixes-2024-06-01' of https://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=147e4dd2980000
kernel config: https://syzkaller.appspot.com/x/.config?x=b639694183430f97
dashboard link: https://syzkaller.appspot.com/bug?extid=de29a1c2404d1300e05a
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ad7392539585/disk-cc8ed4d0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/40401cb5cb4c/vmlinux-cc8ed4d0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f994ac0c05b7/bzImage-cc8ed4d0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+de29a1...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_receive_char / n_tty_write

write to 0xffffc90001379028 of 8 bytes by task 18695 on cpu 0:
commit_echoes drivers/tty/n_tty.c:758 [inline]
n_tty_receive_char+0x4c4/0x680 drivers/tty/n_tty.c:1437
n_tty_receive_buf_standard+0x4bd/0x2e30 drivers/tty/n_tty.c:1606
__receive_buf drivers/tty/n_tty.c:1630 [inline]
n_tty_receive_buf_common+0x7e5/0xbd0 drivers/tty/n_tty.c:1729
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1775
tty_ldisc_receive_buf+0x63/0x100 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+0x1ce/0x410 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3231 [inline]
process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
worker_thread+0x526/0x730 kernel/workqueue.c:3393
kthread+0x1d1/0x210 kernel/kthread.c:389
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

read to 0xffffc90001379028 of 8 bytes by task 6953 on cpu 1:
process_echoes drivers/tty/n_tty.c:784 [inline]
n_tty_write+0x162/0xb90 drivers/tty/n_tty.c:2365
iterate_tty_write drivers/tty/tty_io.c:1021 [inline]
file_tty_write+0x386/0x690 drivers/tty/tty_io.c:1096
tty_write+0x28/0x30 drivers/tty/tty_io.c:1117
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x78f/0x900 fs/read_write.c:590
ksys_write+0xeb/0x1b0 fs/read_write.c:643
__do_sys_write fs/read_write.c:655 [inline]
__se_sys_write fs/read_write.c:652 [inline]
__x64_sys_write+0x42/0x50 fs/read_write.c:652
x64_sys_call+0x27ef/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0x000000000000000c

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6953 Comm: syz-executor.2 Not tainted 6.10.0-rc1-syzkaller-00267-gcc8ed4d0a848 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
==================================================================


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