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BUG: KCSAN: data-race in snd_rawmidi_poll / snd_rawmidi_transmit

write to 0xffff888121b53578 of 8 bytes by task 3225 on cpu 1:
 __snd_rawmidi_transmit_ack sound/core/rawmidi.c:1255 [inline]
 snd_rawmidi_transmit+0x2e6/0x410 sound/core/rawmidi.c:1314
 snd_vmidi_output_work+0xf1/0x200 sound/core/seq/seq_virmidi.c:144
 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 0xffff888121b53578 of 8 bytes by task 10284 on cpu 0:
 snd_rawmidi_ready sound/core/rawmidi.c:102 [inline]
 snd_rawmidi_poll+0x1ce/0x210 sound/core/rawmidi.c:1506
 vfs_poll include/linux/poll.h:90 [inline]
 do_select+0x8f6/0xf70 fs/select.c:534
 core_sys_select+0x3e3/0x610 fs/select.c:677
 do_pselect fs/select.c:759 [inline]
 __do_sys_pselect6 fs/select.c:800 [inline]
 __se_sys_pselect6+0x248/0x290 fs/select.c:791
 __x64_sys_pselect6+0x74/0x80 fs/select.c:791
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10284 Comm: syz-executor.5 Not tainted 5.8.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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