[moderation] [serial?] KCSAN: data-race in n_tty_receive_char / n_tty_write (13)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 818bebeb63dd drm/xe: Don't hand out the flat CCS storage a..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1576fa25580000
kernel config: https://syzkaller.appspot.com/x/.config?x=947a25829226a79e
dashboard link: https://syzkaller.appspot.com/bug?extid=39ea3f4b6fd24a1ca1ca
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
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/55a5d2676f16/disk-818bebeb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ee945f7ee864/vmlinux-818bebeb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3c006b10822c/bzImage-818bebeb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+39ea3f...@syzkaller.appspotmail.com

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

write to 0xffffc9000109b028 of 8 bytes by task 7247 on cpu 0:
commit_echoes drivers/tty/n_tty.c:738 [inline]
n_tty_receive_char+0x44e/0x6d0 drivers/tty/n_tty.c:1413
n_tty_receive_buf_standard+0x563/0x3cb0 drivers/tty/n_tty.c:1582
__receive_buf drivers/tty/n_tty.c:1616 [inline]
n_tty_receive_buf_common+0x821/0xc10 drivers/tty/n_tty.c:1715
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1759
tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:394
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:452 [inline]
flush_to_ldisc+0x13a/0x330 drivers/tty/tty_buffer.c:502
process_one_work kernel/workqueue.c:3387 [inline]
process_scheduled_works+0x56a/0xa50 kernel/workqueue.c:3470
worker_thread+0x569/0x750 kernel/workqueue.c:3551
kthread+0x223/0x270 kernel/kthread.c:436
ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffc9000109b028 of 8 bytes by task 15407 on cpu 1:
process_echoes drivers/tty/n_tty.c:762 [inline]
n_tty_write+0x178/0xb00 drivers/tty/n_tty.c:2352
iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
file_tty_write+0x392/0x6a0 drivers/tty/tty_io.c:1054
tty_write+0x25/0x30 drivers/tty/tty_io.c:1075
iter_file_splice_write+0x6a0/0xa60 fs/splice.c:736
do_splice_from fs/splice.c:936 [inline]
direct_splice_actor+0x158/0x280 fs/splice.c:1159
splice_direct_to_actor+0x2f9/0x680 fs/splice.c:1103
do_splice_direct_actor fs/splice.c:1202 [inline]
do_splice_direct+0x119/0x1a0 fs/splice.c:1228
do_sendfile+0x37d/0x640 fs/read_write.c:1371
__do_sys_sendfile64 fs/read_write.c:1432 [inline]
__se_sys_sendfile64 fs/read_write.c:1418 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1418
x64_sys_call+0x1015/0x2550 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000039 -> 0x000000000000003f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 15407 Comm: syz.4.3643 Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================


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