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BUG: KCSAN: data-race in __dev_open / tun_get_user

write to 0xffff8880978ec228 of 4 bytes by task 23365 on cpu 1:
 __dev_open+0x1be/0x290 net/core/dev.c:1443
 __dev_change_flags+0x363/0x4b0 net/core/dev.c:8143
 dev_change_flags+0x62/0xd0 net/core/dev.c:8214
 dev_ifsioc+0x208/0x6a0 net/core/dev_ioctl.c:244
 dev_ioctl+0x13b/0x630 net/core/dev_ioctl.c:496
 sock_do_ioctl+0xdb/0x230 net/socket.c:1076
 sock_ioctl+0x3a2/0x5e0 net/socket.c:1204
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x101/0x150 fs/ioctl.c:763
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl fs/ioctl.c:770 [inline]
 __x64_sys_ioctl+0x47/0x60 fs/ioctl.c:770
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880978ec228 of 4 bytes by task 23380 on cpu 0:
 tun_get_user+0x11e3/0x25e0 drivers/net/tun.c:1924
 tun_chr_write_iter+0x75/0xc0 drivers/net/tun.c:1991
 call_write_iter include/linux/fs.h:1907 [inline]
 new_sync_write+0x303/0x400 fs/read_write.c:484
 __vfs_write+0x9e/0xb0 fs/read_write.c:497
 vfs_write fs/read_write.c:559 [inline]
 vfs_write+0x189/0x380 fs/read_write.c:543
 ksys_write+0xc5/0x1a0 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+0x49/0x60 fs/read_write.c:621
 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: 23380 Comm: syz-executor.4 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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