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BUG: KCSAN: data-race in snd_rawmidi_transmit / snd_rawmidi_write

read-write to 0xffff888134241638 of 8 bytes by task 2050 on cpu 1:
 __snd_rawmidi_transmit_ack sound/core/rawmidi.c:1267 [inline]
 snd_rawmidi_transmit+0x2b0/0x390 sound/core/rawmidi.c:1326
 snd_vmidi_output_work+0xf1/0x200 sound/core/seq/seq_virmidi.c:144
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff888134241638 of 8 bytes by task 6923 on cpu 0:
 snd_rawmidi_write+0x5ef/0x720 sound/core/rawmidi.c:1489
 vfs_write+0x21a/0x7c0 fs/read_write.c:603
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 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: 6923 Comm: syz-executor.4 Not tainted 5.11.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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