[moderation] [sound?] KCSAN: data-race in snd_seq_fifo_event_in / snd_seq_fifo_poll_wait (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cd89d487374c Merge tag '6.17-rc6-smb3-client-fixes' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1177a0e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6e0c213d0735f5dd
dashboard link: https://syzkaller.appspot.com/bug?extid=87f6b42e66967416c189
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [linux-...@vger.kernel.org linux...@vger.kernel.org pe...@perex.cz ti...@suse.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/fc2828b7b602/disk-cd89d487.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f8144cce2d27/vmlinux-cd89d487.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2dfeac647538/bzImage-cd89d487.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+87f6b4...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in snd_seq_fifo_event_in / snd_seq_fifo_poll_wait

read-write to 0xffff88811aba7738 of 4 bytes by task 4455 on cpu 1:
snd_seq_fifo_event_in+0x155/0x200 sound/core/seq/seq_fifo.c:126
__snd_seq_deliver_single_event sound/core/seq/seq_clientmgr.c:647 [inline]
snd_seq_deliver_single_event+0x3db/0x590 sound/core/seq/seq_clientmgr.c:714
snd_seq_deliver_event+0x181/0x470 sound/core/seq/seq_clientmgr.c:850
snd_seq_kernel_client_dispatch+0x24c/0x260 sound/core/seq/seq_clientmgr.c:2554
snd_seq_system_notify+0x95/0xb0 sound/core/seq/seq_system.c:101
snd_seq_client_notify_subscription+0x7f/0xb0 sound/core/seq/seq_clientmgr.c:1518
subscribe_port sound/core/seq/seq_ports.c:445 [inline]
check_and_subscribe_port+0x419/0x620 sound/core/seq/seq_ports.c:520
snd_seq_port_connect+0x188/0x270 sound/core/seq/seq_ports.c:601
snd_seq_ioctl_subscribe_port+0x22b/0x3b0 sound/core/seq/seq_clientmgr.c:1551
snd_seq_ioctl+0x17a/0x2e0 sound/core/seq/seq_clientmgr.c:2385
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:598 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:584
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:584
x64_sys_call+0x1816/0x2ff0 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 0xffff88811aba7738 of 4 bytes by task 4439 on cpu 0:
snd_seq_fifo_poll_wait+0x68/0x90 sound/core/seq/seq_fifo.c:216
snd_seq_poll+0xa1/0x140 sound/core/seq/seq_clientmgr.c:1160
vfs_poll include/linux/poll.h:82 [inline]
__io_arm_poll_handler+0x1ee/0xb70 io_uring/poll.c:581
io_poll_add+0x69/0xe0 io_uring/poll.c:901
__io_issue_sqe+0xfb/0x2e0 io_uring/io_uring.c:1771
io_issue_sqe+0x53/0x970 io_uring/io_uring.c:1794
io_queue_sqe io_uring/io_uring.c:2023 [inline]
io_submit_sqe io_uring/io_uring.c:2283 [inline]
io_submit_sqes+0x675/0x1060 io_uring/io_uring.c:2396
__do_sys_io_uring_enter io_uring/io_uring.c:3463 [inline]
__se_sys_io_uring_enter+0x1c1/0x1b70 io_uring/io_uring.c:3397
__x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:3397
x64_sys_call+0x2de1/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:427
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

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4439 Comm: syz.4.301 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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