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BUG: KCSAN: data-race in snd_rawmidi_drain_output / snd_rawmidi_transmit

write to 0xffff88810c70f878 of 8 bytes by task 2917 on cpu 0:
 __snd_rawmidi_transmit_ack sound/core/rawmidi.c:1267 [inline]
 snd_rawmidi_transmit+0x2b8/0x3b0 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+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88810c70f878 of 8 bytes by task 16687 on cpu 1:
 snd_rawmidi_drain_output+0x141/0x440 sound/core/rawmidi.c:232
 close_substream+0x14c/0x2e0 sound/core/rawmidi.c:520
 rawmidi_release_priv+0x96/0xf0 sound/core/rawmidi.c:546
 snd_rawmidi_release+0x33/0x80 sound/core/rawmidi.c:577
 __fput+0x263/0x4f0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0x8e/0x110 kernel/task_work.c:140
 exit_task_work include/linux/task_work.h:30 [inline]
 do_exit+0x471/0x15e0 kernel/exit.c:825
 do_group_exit+0xce/0x180 kernel/exit.c:922
 get_signal+0xf93/0x1510 kernel/signal.c:2781
 arch_do_signal_or_restart+0x2a/0x270 arch/x86/kernel/signal.c:789
 handle_signal_work kernel/entry/common.c:147 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x11a/0x1b0 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 16687 Comm: syz-executor.5 Tainted: G        W         5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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