[moderation] [serial?] KCSAN: data-race in n_tty_check_unthrottle / n_tty_receive_buf_common (13)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 92b71befc349 Merge tag 'objtool-urgent-2025-04-01' of git:..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14a0cfb0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a8120cade23cf14e
dashboard link: https://syzkaller.appspot.com/bug?extid=98d1723c756a6f0e7929
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/2e7df7bc2f52/disk-92b71bef.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/be59123d5efb/vmlinux-92b71bef.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7c9eff86053e/bzImage-92b71bef.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+98d172...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_check_unthrottle / n_tty_receive_buf_common

write to 0xffff8881179975dc of 4 bytes by task 5221 on cpu 0:
tty_set_flow_change drivers/tty/tty.h:59 [inline]
n_tty_check_unthrottle+0xdd/0x1d0 drivers/tty/n_tty.c:280
n_tty_read+0xab3/0xd30 drivers/tty/n_tty.c:2312
iterate_tty_read drivers/tty/tty_io.c:856 [inline]
tty_read+0x15a/0x480 drivers/tty/tty_io.c:931
new_sync_read fs/read_write.c:489 [inline]
vfs_read+0x5e6/0x710 fs/read_write.c:570
ksys_read+0xeb/0x1b0 fs/read_write.c:713
__do_sys_read fs/read_write.c:722 [inline]
__se_sys_read fs/read_write.c:720 [inline]
__x64_sys_read+0x42/0x50 fs/read_write.c:720
x64_sys_call+0x2a3b/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:1
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff8881179975dc of 4 bytes by task 5225 on cpu 1:
n_tty_receive_buf_common+0xaf4/0xbe0 drivers/tty/n_tty.c:-1
n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1779
tiocsti+0x16b/0x1d0 drivers/tty/tty_io.c:2299
tty_ioctl+0x409/0xbe0 drivers/tty/tty_io.c:2716
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0xc9/0x140 fs/ioctl.c:892
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
x64_sys_call+0x168d/0x2e10 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000001 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5225 Comm: syz.3.655 Not tainted 6.14.0-syzkaller-12508-g92b71befc349 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.