[PATCH v2 2/2] reboot: fix parsing of reboot cpu number

[Matteo Croce <mcroce@linux.microsoft.com>]

From: Matteo Croce <mcroce@microsoft.com>

The kernel cmdline reboot= argument allows to specify the CPU used
for rebooting, with the syntax `s####` among the other flags, e.g.

  reboot=soft,s4
  reboot=warm,s31,force

In the early days the parsing was done with simple_strtoul(), later
deprecated in favor of the safer kstrtoint() which handles overflow.

But kstrtoint() returns -EINVAL if there are non-digit characters
in a string, so if this flag is not the last given, it's silently
ignored as well as the subsequent ones.

To fix it, revert the usage of simple_strtoul(), which is no longer
deprecated, and restore the old behaviour.

While at it, merge two identical code blocks into one.

Fixes: 616feab75397 ("kernel/reboot.c: convert simple_strtoul to kstrtoint")
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
---
 kernel/reboot.c | 30 ++++++++++++------------------
 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index c4e7965c39b9..a09c5937c0b6 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -552,25 +552,19 @@ static int __init reboot_setup(char *str)
 
 		case 's':
 		{
-			int rc;
-
-			if (isdigit(*(str+1))) {
-				rc = kstrtoint(str+1, 0, &reboot_cpu);
-				if (rc)
-					return rc;
-				if (reboot_cpu >= num_possible_cpus()) {
-					reboot_cpu = 0;
-					return -ERANGE;
-				}
-			} else if (str[1] == 'm' && str[2] == 'p' &&
-				   isdigit(*(str+3))) {
-				rc = kstrtoint(str+3, 0, &reboot_cpu);
-				if (rc)
-					return rc;
-				if (reboot_cpu >= num_possible_cpus()) {
-					reboot_cpu = 0;
+			int cpu;
+
+			/*
+			 * reboot_cpu is s[mp]#### with #### being the processor
+			 * to be used for rebooting. Skip 's' or 'smp' prefix.
+			 */
+			str += str[1] == 'm' && str[2] == 'p' ? 3 : 1;
+
+			if (isdigit(str[0])) {
+				cpu = simple_strtoul(str, NULL, 0);
+				if (cpu >= num_possible_cpus())
 					return -ERANGE;
-				}
+				reboot_cpu = cpu;
 			} else
 				*mode = REBOOT_SOFT;
 			break;
-- 
2.28.0