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BUG: KCSAN: data-race in __snd_rawmidi_transmit_ack / snd_rawmidi_write

write to 0xffff88809ec3d878 of 8 bytes by task 2520 on cpu 0:
 __snd_rawmidi_transmit_ack+0xcc/0x1c0 sound/core/rawmidi.c:1234
 snd_rawmidi_transmit+0x91/0xc0 sound/core/rawmidi.c:1293
 snd_vmidi_output_work+0xaf/0x1f0 sound/core/seq/seq_virmidi.c:143
 process_one_work+0x424/0x930 kernel/workqueue.c:2264
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2410
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff88809ec3d878 of 8 bytes by task 19778 on cpu 1:
 snd_rawmidi_write+0x5ce/0x740 sound/core/rawmidi.c:1424
 __vfs_write+0x58/0xb0 fs/read_write.c:494
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x189/0x380 fs/read_write.c:542
 ksys_write+0x16a/0x1a0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x49/0x60 fs/read_write.c:620
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19778 Comm: syz-executor.4 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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