powerpc/kdump: Only save CPU state first time through the secondary C…

…PU capture code

We might enter the secondary CPU capture code twice, eg if we have to
unstick some CPUs with a system reset. In this case we don't want to
overwrite the state on CPUs that had made it into the capture code OK,
so use the cpus_state_saved cpumask for that and make it local to
crash_ipi_callback.

For controlling progress now use atomic_t cpus_in_crash to count how
many CPUs have made it into the kdump code, and time_to_dump to tell
everyone it's time to dump.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/crash.c

@@ -46,7 +46,8 @@
 
 /* This keeps a track of which one is the crashing cpu. */
 int crashing_cpu = -1;
-static cpumask_t cpus_in_crash = CPU_MASK_NONE;
+static atomic_t cpus_in_crash;
+static int time_to_dump;
 
 #define CRASH_HANDLER_MAX 3
 /* NULL terminated list of shutdown handles */
@@ -67,21 +68,27 @@ static int handle_fault(struct pt_regs *regs)
 
 void crash_ipi_callback(struct pt_regs *regs)
 {
+	static cpumask_t cpus_state_saved = CPU_MASK_NONE;
+
 	int cpu = smp_processor_id();
 
 	if (!cpu_online(cpu))
 		return;
 
 	hard_irq_disable();
-	if (!cpumask_test_cpu(cpu, &cpus_in_crash))
+	if (!cpumask_test_cpu(cpu, &cpus_state_saved)) {
 		crash_save_cpu(regs, cpu);
-	cpumask_set_cpu(cpu, &cpus_in_crash);
+		cpumask_set_cpu(cpu, &cpus_state_saved);
+	}
+
+	atomic_inc(&cpus_in_crash);
+	smp_mb__after_atomic_inc();
 
 	/*
 	 * Starting the kdump boot.
 	 * This barrier is needed to make sure that all CPUs are stopped.
 	 */
-	while (!cpumask_test_cpu(crashing_cpu, &cpus_in_crash))
+	while (!time_to_dump)
 		cpu_relax();
 
 	if (ppc_md.kexec_cpu_down)
@@ -115,19 +122,18 @@ static void crash_kexec_prepare_cpus(int cpu)
 	 * respond.
 	 */
 	msecs = IPI_TIMEOUT;
-	while ((cpumask_weight(&cpus_in_crash) < ncpus) && (--msecs > 0)) {
+	while ((atomic_read(&cpus_in_crash) < ncpus) && (--msecs > 0))
 		mdelay(1);
-	}
 
 	/* Would it be better to replace the trap vector here? */
 
-	if (cpumask_weight(&cpus_in_crash) >= ncpus) {
+	if (atomic_read(&cpus_in_crash) >= ncpus) {
 		printk(KERN_EMERG "IPI complete\n");
 		return;
 	}
 
 	printk(KERN_EMERG "ERROR: %d cpu(s) not responding\n",
-		ncpus - cpumask_weight(&cpus_in_crash));
+		ncpus - atomic_read(&cpus_in_crash));
 
 	/*
 	 * If we have a panic timeout set then we can't wait indefinitely
@@ -155,10 +161,10 @@ static void crash_kexec_prepare_cpus(int cpu)
 		 * crash code again. We need to reset cpus_in_crash so we
 		 * wait for everyone to do this.
 		 */
-		cpus_in_crash = CPU_MASK_NONE;
+		atomic_set(&cpus_in_crash, 0);
 		smp_mb();
 
-		while (cpumask_weight(&cpus_in_crash) < ncpus)
+		while (atomic_read(&cpus_in_crash) < ncpus)
 			cpu_relax();
 	}
 
@@ -316,7 +322,6 @@ void default_machine_crash_shutdown(struct pt_regs *regs)
 	 * such that another IPI will not be sent.
 	 */
 	crashing_cpu = smp_processor_id();
-	crash_save_cpu(regs, crashing_cpu);
 
 	/*
 	 * If we came in via system reset, wait a while for the secondary
@@ -326,7 +331,11 @@ void default_machine_crash_shutdown(struct pt_regs *regs)
 		mdelay(PRIMARY_TIMEOUT);
 
 	crash_kexec_prepare_cpus(crashing_cpu);
-	cpumask_set_cpu(crashing_cpu, &cpus_in_crash);
+
+	crash_save_cpu(regs, crashing_cpu);
+
+	time_to_dump = 1;
+
 	crash_kexec_wait_realmode(crashing_cpu);
 
 	machine_kexec_mask_interrupts();