Update Linux to v5.4.148

Sourced from [1]

[1] https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.4.148.tar.gz

Change-Id: Ib3d26c5ba9b022e2e03533005c4fed4d7c30b61b
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index e2a46cf..890f951 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -8,6 +8,7 @@
  * Copyright 2018 Nick Piggin, Michael Ellerman, IBM Corp.
  */
 
+#include <linux/delay.h>
 #include <linux/export.h>
 #include <linux/kallsyms.h>
 #include <linux/module.h>
@@ -19,6 +20,7 @@
 #include <asm/ptrace.h>
 #include <asm/processor.h>
 #include <linux/ftrace.h>
+#include <linux/delay.h>
 #include <asm/kprobes.h>
 
 #include <asm/paca.h>
@@ -230,17 +232,31 @@
 
 static void raise_backtrace_ipi(cpumask_t *mask)
 {
+	struct paca_struct *p;
 	unsigned int cpu;
+	u64 delay_us;
 
 	for_each_cpu(cpu, mask) {
-		if (cpu == smp_processor_id())
+		if (cpu == smp_processor_id()) {
 			handle_backtrace_ipi(NULL);
-		else
-			smp_send_safe_nmi_ipi(cpu, handle_backtrace_ipi, 5 * USEC_PER_SEC);
-	}
+			continue;
+		}
 
-	for_each_cpu(cpu, mask) {
-		struct paca_struct *p = paca_ptrs[cpu];
+		delay_us = 5 * USEC_PER_SEC;
+
+		if (smp_send_safe_nmi_ipi(cpu, handle_backtrace_ipi, delay_us)) {
+			// Now wait up to 5s for the other CPU to do its backtrace
+			while (cpumask_test_cpu(cpu, mask) && delay_us) {
+				udelay(1);
+				delay_us--;
+			}
+
+			// Other CPU cleared itself from the mask
+			if (delay_us)
+				continue;
+		}
+
+		p = paca_ptrs[cpu];
 
 		cpumask_clear_cpu(cpu, mask);