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BUG: KCSAN: data-race in snd_rawmidi_proceed / snd_rawmidi_write

write to 0xffff888121f2cab8 of 8 bytes by task 3223 on cpu 0:
 __snd_rawmidi_transmit_ack sound/core/rawmidi.c:1255 [inline]
 snd_rawmidi_proceed+0x126/0x260 sound/core/rawmidi.c:1336
 snd_vmidi_output_work+0x8e/0x200 sound/core/seq/seq_virmidi.c:139
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

read to 0xffff888121f2cab8 of 8 bytes by task 19132 on cpu 1:
 snd_rawmidi_write+0x2dd/0x6b0 sound/core/rawmidi.c:1447
 __vfs_write+0x69/0x340 fs/read_write.c:495
 __kernel_write+0xd1/0x240 fs/read_write.c:516
 write_pipe_buf+0x96/0xc0 fs/splice.c:799
 splice_from_pipe_feed fs/splice.c:502 [inline]
 __splice_from_pipe+0x1f7/0x4f0 fs/splice.c:626
 splice_from_pipe fs/splice.c:661 [inline]
 default_file_splice_write fs/splice.c:811 [inline]
 do_splice_from fs/splice.c:847 [inline]
 direct_splice_actor+0xee/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1521
 __do_sys_sendfile64 fs/read_write.c:1582 [inline]
 __se_sys_sendfile64 fs/read_write.c:1568 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1568
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19132 Comm: syz-executor.2 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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