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BUG: KCSAN: data-race in __snd_rawmidi_transmit_ack / snd_rawmidi_poll

write to 0xffff8880aee34ab8 of 8 bytes by task 3440 on cpu 1:
 __snd_rawmidi_transmit_ack+0xcc/0x1c0 sound/core/rawmidi.c:1234
 snd_rawmidi_transmit+0x8c/0xc0 sound/core/rawmidi.c:1293
 snd_vmidi_output_work+0xaf/0x1f0 sound/core/seq/seq_virmidi.c:144
 process_one_work+0x424/0x930 kernel/workqueue.c:2268
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
 kthread+0x203/0x230 kernel/kthread.c:268
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8880aee34ab8 of 8 bytes by task 11270 on cpu 0:
 snd_rawmidi_ready sound/core/rawmidi.c:102 [inline]
 snd_rawmidi_poll+0x1db/0x300 sound/core/rawmidi.c:1483
 vfs_poll include/linux/poll.h:90 [inline]
 do_select+0x7cf/0x1020 fs/select.c:534
 core_sys_select+0x2c7/0x5f0 fs/select.c:677
 do_pselect.constprop.0+0x125/0x160 fs/select.c:759
 __do_sys_pselect6 fs/select.c:784 [inline]
 __se_sys_pselect6 fs/select.c:769 [inline]
 __x64_sys_pselect6+0x12a/0x160 fs/select.c:769
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11270 Comm: syz-executor.5 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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