[moderation] [sound?] KCSAN: data-race in snd_seq_fifo_cell_out / snd_seq_fifo_poll_wait

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8f5ae30d69d7 Linux 6.17-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10424af0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e229060118f4fc05
dashboard link: https://syzkaller.appspot.com/bug?extid=c3dbc239259940ededba
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
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/09bc520c1da6/disk-8f5ae30d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d721e73ea778/vmlinux-8f5ae30d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/02de5d4dd2f6/bzImage-8f5ae30d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c3dbc2...@syzkaller.appspotmail.com

EXT4-fs (loop4): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
ext4 filesystem being mounted at /478/file0 supports timestamps until 2038-01-19 (0x7fffffff)
==================================================================
BUG: KCSAN: data-race in snd_seq_fifo_cell_out / snd_seq_fifo_poll_wait

read-write to 0xffff8881184a5eb8 of 4 bytes by task 10533 on cpu 0:
fifo_cell_out sound/core/seq/seq_fifo.c:153 [inline]
snd_seq_fifo_cell_out+0x222/0x270 sound/core/seq/seq_fifo.c:173
snd_seq_read+0x1c8/0x410 sound/core/seq/seq_clientmgr.c:478
loop_rw_iter+0x2c3/0x3f0 include/linux/uio.h:-1
io_iter_do_read io_uring/rw.c:830 [inline]
__io_read+0xbcb/0xc20 io_uring/rw.c:941
io_read+0x1c/0x60 io_uring/rw.c:1020
__io_issue_sqe+0xfb/0x2e0 io_uring/io_uring.c:1773
io_issue_sqe+0x53/0x970 io_uring/io_uring.c:1796
io_wq_submit_work+0x3f7/0x5f0 io_uring/io_uring.c:1908
io_worker_handle_work+0x44e/0x9b0 io_uring/io-wq.c:642
io_wq_worker+0x22e/0x870 io_uring/io-wq.c:696
ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff8881184a5eb8 of 4 bytes by task 10526 on cpu 1:
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_file_supports_nowait io_uring/rw.c:46 [inline]
__io_read+0x2e7/0xc20 io_uring/rw.c:927
io_read+0x1c/0x60 io_uring/rw.c:1020
__io_issue_sqe+0xfb/0x2e0 io_uring/io_uring.c:1773
io_issue_sqe+0x53/0x970 io_uring/io_uring.c:1796
io_queue_sqe io_uring/io_uring.c:2025 [inline]
io_req_task_submit+0x6b/0xd0 io_uring/io_uring.c:1415
io_handle_tw_list+0x18d/0x1c0 io_uring/io_uring.c:1102
tctx_task_work_run+0x6d/0x1a0 io_uring/io_uring.c:1167
tctx_task_work+0x3f/0x80 io_uring/io_uring.c:1185
task_work_run+0x12e/0x1a0 kernel/task_work.c:227
get_signal+0xe13/0xf70 kernel/signal.c:2807
arch_do_signal_or_restart+0x96/0x480 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x7a/0x100 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000001 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 10526 Comm: syz.4.2244 Not tainted 6.17.0-rc1-syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================


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