KCSAN: data-race in snd_rawmidi_poll / snd_rawmidi_transmit

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 418baf2c Linux 5.10-rc5
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1105317d500000
kernel config: https://syzkaller.appspot.com/x/.config?x=cf114765a0c30afa
dashboard link: https://syzkaller.appspot.com/bug?extid=35554d6d9ffc6996c69a
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [alsa-...@alsa-project.org ar...@arndb.de baoli...@linaro.org linux-...@vger.kernel.org pe...@perex.cz pierre-lou...@linux.intel.com 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+35554d...@syzkaller.appspotmail.com

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

read-write to 0xffff88813ac14b78 of 8 bytes by task 2979 on cpu 0:
__snd_rawmidi_transmit_ack sound/core/rawmidi.c:1255 [inline]
snd_rawmidi_transmit+0x2a7/0x390 sound/core/rawmidi.c:1314
snd_vmidi_output_work+0xf1/0x200 sound/core/seq/seq_virmidi.c:144
process_one_work+0x3e1/0x950 kernel/workqueue.c:2272
worker_thread+0x635/0xb90 kernel/workqueue.c:2418
kthread+0x1fd/0x220 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88813ac14b78 of 8 bytes by task 25811 on cpu 1:
snd_rawmidi_ready sound/core/rawmidi.c:102 [inline]
snd_rawmidi_poll+0x1ce/0x210 sound/core/rawmidi.c:1506
vfs_poll include/linux/poll.h:90 [inline]
do_select+0x8e4/0xf30 fs/select.c:534
core_sys_select+0x41f/0x670 fs/select.c:677
do_pselect fs/select.c:759 [inline]
__do_sys_pselect6+0x1bf/0x220 fs/select.c:800
__se_sys_pselect6 fs/select.c:791 [inline]
__x64_sys_pselect6+0x74/0x80 fs/select.c:791
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: 1 PID: 25811 Comm: syz-executor.3 Not tainted 5.10.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

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