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BUG: KCSAN: data-race in snd_rawmidi_transmit / snd_rawmidi_write

write to 0xffff88801d7a3cf8 of 8 bytes by task 3248 on cpu 1:
 __snd_rawmidi_transmit_ack sound/core/rawmidi.c:1255 [inline]
 snd_rawmidi_transmit+0x2e5/0x400 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+0x1ff/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88801d7a3cf8 of 8 bytes by task 14582 on cpu 0:
 snd_rawmidi_write+0x597/0x6b0 sound/core/rawmidi.c:1475
 __kernel_write+0x124/0x5f0 fs/read_write.c:528
 write_pipe_buf+0x96/0xc0 fs/splice.c:818
 splice_from_pipe_feed fs/splice.c:501 [inline]
 __splice_from_pipe+0x222/0x4d0 fs/splice.c:645
 splice_from_pipe fs/splice.c:680 [inline]
 default_file_splice_write fs/splice.c:830 [inline]
 do_splice_from fs/splice.c:866 [inline]
 direct_splice_actor+0xee/0x150 fs/splice.c:1035
 splice_direct_to_actor+0x365/0x660 fs/splice.c:990
 do_splice_direct+0xf5/0x170 fs/splice.c:1078
 do_sendfile+0x574/0xb70 fs/read_write.c:1238
 __do_sys_sendfile64 fs/read_write.c:1299 [inline]
 __se_sys_sendfile64 fs/read_write.c:1285 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1285
 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: 14582 Comm: syz-executor.5 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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