x86/kdump: make crash kernel boot faster

euleros inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SJBG?from=project-issue
CVE: NA

---------------------------

If other cpus offline before handle the crash NMI, the
waiting_for_crash_ipi can not be decreased to 0, and
current cpu will wait 1 second. So break if all other
cpus offline.
Signed-off-by: NBin Wang <wangbin224@huawei.com>
Reviewed-by: Nluo chunsheng <luochunsheng@huawei.com>
Reviewed-by: NYang Jihong <yangjihong1@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/x86/kernel/reboot.c

@@ -871,6 +871,14 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 
 	msecs = 1000; /* Wait at most a second for the other cpus to stop */
 	while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
+		/*
+		 * If other cpus offline before handle the crash NMI, the
+		 * waiting_for_crash_ipi can not be decreased to 0, and
+		 * current cpu will wait 1 second. So break if all other
+		 * cpus offline.
+		 */
+		if (num_online_cpus() == 1)
+			break;
 		mdelay(1);
 		msecs--;
 	}