KCSAN: data-race in snd_rawmidi_transmit / snd_rawmidi_write

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fb893de3 Merge tag 'tag-chrome-platform-for-v5.9' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12e75e6a900000
kernel config: https://syzkaller.appspot.com/x/.config?x=eb948cec8745bdce
dashboard link: https://syzkaller.appspot.com/bug?extid=a23a6f1215c84756577c
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
CC: [alsa-...@alsa-project.org ar...@arndb.de baoli...@linaro.org linux-...@vger.kernel.org pe...@perex.cz ti...@suse.com]

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a23a6f...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in snd_rawmidi_transmit / snd_rawmidi_write

write to 0xffff8881215e31b8 of 8 bytes by task 3254 on cpu 1:
__snd_rawmidi_transmit_ack sound/core/rawmidi.c:1255 [inline]
snd_rawmidi_transmit+0x2e6/0x410 sound/core/rawmidi.c:1314
snd_vmidi_output_work+0xf1/0x200 sound/core/seq/seq_virmidi.c:144
process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
kthread+0x20d/0x230 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881215e31b8 of 8 bytes by task 11097 on cpu 0:
snd_rawmidi_write+0x2dd/0x6b0 sound/core/rawmidi.c:1447
vfs_write+0x1df/0x6f0 fs/read_write.c:576
ksys_write+0xce/0x180 fs/read_write.c:631
__do_sys_write fs/read_write.c:643 [inline]
__se_sys_write fs/read_write.c:640 [inline]
__x64_sys_write+0x3e/0x50 fs/read_write.c:640
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11097 Comm: syz-executor.3 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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