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BUG: KCSAN: data-race in mISDN_ioctl / mISDN_read

write to 0xffff88813837e3c0 of 4 bytes by task 11588 on cpu 1:
 misdn_add_timer drivers/isdn/mISDN/timerdev.c:175 [inline]
 mISDN_ioctl+0x2aa/0x590 drivers/isdn/mISDN/timerdev.c:233
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:860
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813837e3c0 of 4 bytes by task 11587 on cpu 0:
 mISDN_read+0x159/0x4b0 drivers/isdn/mISDN/timerdev.c:112
 vfs_read+0x1e6/0x750 fs/read_write.c:479
 ksys_read+0xd9/0x190 fs/read_write.c:619
 __do_sys_read fs/read_write.c:629 [inline]
 __se_sys_read fs/read_write.c:627 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:627
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11587 Comm: syz-executor.1 Not tainted 5.17.0-rc5-syzkaller-00004-g038101e6b2cd-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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