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BUG: KCSAN: data-race in snd_pcm_drop / snd_pcm_stop

write to 0xffff888086ba8000 of 4 bytes by task 19853 on cpu 0:
 snd_pcm_post_stop sound/core/pcm_native.c:1430 [inline]
 snd_pcm_action_single sound/core/pcm_native.c:1209 [inline]
 snd_pcm_action sound/core/pcm_native.c:1290 [inline]
 snd_pcm_stop+0x276/0x330 sound/core/pcm_native.c:1455
 snd_pcm_drop+0x122/0x1a0 sound/core/pcm_native.c:2133
 snd_pcm_kernel_ioctl+0x19d/0xc20 sound/core/pcm_native.c:3335
 snd_pcm_oss_set_trigger+0x3e9/0x490 sound/core/oss/pcm_oss.c:2102
 snd_pcm_oss_ioctl+0xce3/0x2970 sound/core/oss/pcm_oss.c:2680
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888086ba8000 of 4 bytes by task 19847 on cpu 1:
 snd_pcm_drop+0x4f/0x1a0 sound/core/pcm_native.c:2124
 snd_pcm_kernel_ioctl+0x19d/0xc20 sound/core/pcm_native.c:3335
 snd_pcm_oss_sync+0x17f/0x680 sound/core/oss/pcm_oss.c:1711
 snd_pcm_oss_ioctl+0x613/0x2970 sound/core/oss/pcm_oss.c:2590
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19847 Comm: syz-executor.5 Not tainted 5.9.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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