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BUG: KCSAN: data-race in snd_rawmidi_kernel_write1 / snd_rawmidi_poll

write to 0xffff888095acde78 of 8 bytes by task 1491 on cpu 1:
 snd_rawmidi_kernel_write1+0x1e1/0x430 sound/core/rawmidi.c:1378
 snd_rawmidi_write+0x31b/0x6b0 sound/core/rawmidi.c:1452
 __vfs_write+0x69/0x340 fs/read_write.c:495
 vfs_write+0x19b/0x350 fs/read_write.c:559
 ksys_write+0xce/0x180 fs/read_write.c:612
 __do_sys_write fs/read_write.c:624 [inline]
 __se_sys_write fs/read_write.c:621 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:621
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888095acde78 of 8 bytes by task 1499 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: 1499 Comm: syz-executor.3 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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