linux-kernel - [PATCH v3 3/3] reboot: refactor and comment the cpu selection code

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Date:   Tue,  3 Nov 2020 22:40:25 +0100
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     linux-kernel@...r.kernel.org
Cc:     Guenter Roeck <linux@...ck-us.net>, Petr Mladek <pmladek@...e.com>,
        Arnd Bergmann <arnd@...db.de>, Mike Rapoport <rppt@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Robin Holt <robinmholt@...il.com>,
        Fabian Frederick <fabf@...net.be>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH v3 3/3] reboot: refactor and comment the cpu selection code

From: Matteo Croce <mcroce@...rosoft.com>

Small improvements to the code, without changing the way it works:
- use a local variable, to avoid a small time lapse where reboot_cpu
  can have an invalid value
- comment the code which is not easy to understand at a glance
- merge two identical code blocks into one
- replace pointer arithmetics with equivalent array syntax

Signed-off-by: Matteo Croce <mcroce@...rosoft.com>
---
 kernel/reboot.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index af6f23d8bea1..dd483bde932b 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -551,20 +551,24 @@ static int __init reboot_setup(char *str)
 			break;
 
 		case 's':
-			if (isdigit(*(str+1)))
-				reboot_cpu = simple_strtoul(str+1, NULL, 0);
-			else if (str[1] == 'm' && str[2] == 'p' &&
-							isdigit(*(str+3)))
-				reboot_cpu = simple_strtoul(str+3, NULL, 0);
-			else
+			/*
+			 * 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])) {
+				int cpu = simple_strtoul(str, NULL, 0);
+
+				if (cpu >= num_possible_cpus()) {
+					pr_err("Ignoring the CPU number in reboot= option. "
+					"CPU %d exceeds possible cpu number %d\n",
+					cpu, num_possible_cpus());
+					break;
+				}
+				reboot_cpu = cpu;
+			} else
 				*mode = REBOOT_SOFT;
-			if (reboot_cpu >= num_possible_cpus()) {
-				pr_err("Ignoring the CPU number in reboot= option. "
-				       "CPU %d exceeds possible cpu number %d\n",
-				       reboot_cpu, num_possible_cpus());
-				reboot_cpu = 0;
-				break;
-			}
 			break;
 
 		case 'g':
-- 
2.28.0