powerpc/xmon: Add support for running a command on all cpus in xmon

It is sometimes desirable to run a command on all cpus in xmon. A
typical scenario is to obtain the backtrace from all cpus in xmon if
there is a soft lockup. Add rudimentary support for the same. The
command to be run on all cpus should be prefixed with 'c#'. As an
example, 'c#t' will run 't' command and produce a backtrace on all cpus
in xmon.

Since many xmon commands are not sensible for running in this manner, we
only allow a predefined list of commands -- 'r', 'S' and 't' for now.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210601074801.617363-1-naveen.n.rao@linux.vnet.ibm.com

arch/powerpc/xmon/xmon.c

@@ -70,6 +70,9 @@ static cpumask_t cpus_in_xmon = CPU_MASK_NONE;
 static unsigned long xmon_taken = 1;
 static int xmon_owner;
 static int xmon_gate;
+static int xmon_batch;
+static unsigned long xmon_batch_start_cpu;
+static cpumask_t xmon_batch_cpus = CPU_MASK_NONE;
 #else
 #define xmon_owner 0
 #endif /* CONFIG_SMP */
@@ -133,6 +136,12 @@ static void prdump(unsigned long, long);
 static int ppc_inst_dump(unsigned long, long, int);
 static void dump_log_buf(void);
 
+#ifdef CONFIG_SMP
+static int xmon_switch_cpu(unsigned long);
+static int xmon_batch_next_cpu(void);
+static int batch_cmds(struct pt_regs *);
+#endif
+
 #ifdef CONFIG_PPC_POWERNV
 static void dump_opal_msglog(void);
 #else
@@ -216,7 +225,8 @@ Commands:\n\
 #ifdef CONFIG_SMP
   "\
   c	print cpus stopped in xmon\n\
-  c#	try to switch to cpu number h (in hex)\n"
+  c#	try to switch to cpu number h (in hex)\n\
+  c# $	run command '$' (one of 'r','S' or 't') on all cpus in xmon\n"
 #endif
   "\
   C	checksum\n\
@@ -644,7 +654,12 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
 			spin_cpu_relax();
 			touch_nmi_watchdog();
 		} else {
-			if (!locked_down)
+			cmd = 1;
+#ifdef CONFIG_SMP
+			if (xmon_batch)
+				cmd = batch_cmds(regs);
+#endif
+			if (!locked_down && cmd)
 				cmd = cmds(regs);
 			if (locked_down || cmd != 0) {
 				/* exiting xmon */
@@ -1243,11 +1258,112 @@ static void bootcmds(void)
 	}
 }
 
+#ifdef CONFIG_SMP
+static int xmon_switch_cpu(unsigned long cpu)
+{
+	int timeout;
+
+	xmon_taken = 0;
+	mb();
+	xmon_owner = cpu;
+	timeout = 10000000;
+	while (!xmon_taken) {
+		if (--timeout == 0) {
+			if (test_and_set_bit(0, &xmon_taken))
+				break;
+			/* take control back */
+			mb();
+			xmon_owner = smp_processor_id();
+			printf("cpu 0x%lx didn't take control\n", cpu);
+			return 0;
+		}
+		barrier();
+	}
+	return 1;
+}
+
+static int xmon_batch_next_cpu(void)
+{
+	unsigned long cpu;
+
+	while (!cpumask_empty(&xmon_batch_cpus)) {
+		cpu = cpumask_next_wrap(smp_processor_id(), &xmon_batch_cpus,
+					xmon_batch_start_cpu, true);
+		if (cpu == nr_cpumask_bits)
+			break;
+		if (xmon_batch_start_cpu == -1)
+			xmon_batch_start_cpu = cpu;
+		if (xmon_switch_cpu(cpu))
+			return 0;
+		cpumask_clear_cpu(cpu, &xmon_batch_cpus);
+	}
+
+	xmon_batch = 0;
+	printf("%x:mon> \n", smp_processor_id());
+	return 1;
+}
+
+static int batch_cmds(struct pt_regs *excp)
+{
+	int cmd;
+
+	/* simulate command entry */
+	cmd = xmon_batch;
+	termch = '\n';
+
+	last_cmd = NULL;
+	xmon_regs = excp;
+
+	printf("%x:", smp_processor_id());
+	printf("mon> ");
+	printf("%c\n", (char)cmd);
+
+	switch (cmd) {
+	case 'r':
+		prregs(excp);	/* print regs */
+		break;
+	case 'S':
+		super_regs();
+		break;
+	case 't':
+		backtrace(excp);
+		break;
+	}
+
+	cpumask_clear_cpu(smp_processor_id(), &xmon_batch_cpus);
+
+	return xmon_batch_next_cpu();
+}
+
 static int cpu_cmd(void)
 {
-#ifdef CONFIG_SMP
 	unsigned long cpu, first_cpu, last_cpu;
-	int timeout;
+
+	cpu = skipbl();
+	if (cpu == '#') {
+		xmon_batch = skipbl();
+		if (xmon_batch) {
+			switch (xmon_batch) {
+			case 'r':
+			case 'S':
+			case 't':
+				cpumask_copy(&xmon_batch_cpus, &cpus_in_xmon);
+				if (cpumask_weight(&xmon_batch_cpus) <= 1) {
+					printf("There are no other cpus in xmon\n");
+					break;
+				}
+				xmon_batch_start_cpu = -1;
+				if (!xmon_batch_next_cpu())
+					return 1;
+				break;
+			default:
+				printf("c# only supports 'r', 'S' and 't' commands\n");
+			}
+			xmon_batch = 0;
+			return 0;
+		}
+	}
+	termch = cpu;
 
 	if (!scanhex(&cpu)) {
 		/* print cpus waiting or in xmon */
@@ -1279,27 +1395,15 @@ static int cpu_cmd(void)
 #endif
 		return 0;
 	}
-	xmon_taken = 0;
-	mb();
-	xmon_owner = cpu;
-	timeout = 10000000;
-	while (!xmon_taken) {
-		if (--timeout == 0) {
-			if (test_and_set_bit(0, &xmon_taken))
-				break;
-			/* take control back */
-			mb();
-			xmon_owner = smp_processor_id();
-			printf("cpu 0x%lx didn't take control\n", cpu);
-			return 0;
-		}
-		barrier();
-	}
-	return 1;
+
+	return xmon_switch_cpu(cpu);
+}
 #else
+static int cpu_cmd(void)
+{
 	return 0;
-#endif /* CONFIG_SMP */
 }
+#endif /* CONFIG_SMP */
 
 static unsigned short fcstab[256] = {
 	0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,