linux-kernel - [PATCH] sched/debug: initialize sd_sysctl_cpus if !CONFIG_CPUMASK

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Date:   Tue, 29 Jan 2019 10:12:45 -0500
From:   Masayoshi Mizuma <msys.mizuma@...il.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Cc:     Masayoshi Mizuma <msys.mizuma@...il.com>,
        Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
        Joe Lawrence <joe.lawrence@...hat.com>
Subject: [PATCH] sched/debug: initialize sd_sysctl_cpus if !CONFIG_CPUMASK_OFFSTACK

From: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>

register_sched_domain_sysctl() copies the cpu_possible_mask into
sd_sysctl_cpus, but only if sd_sysctl_cpus hasn't already been
allocated (ie, CONFIG_CPUMASK_OFFSTACK is set).  However, when
CONFIG_CPUMASK_OFFSTACK is not set, sd_sysctl_cpus is left uninitialized
(all zeroes) and the kernel may fail to initialize sched_domain sysctl
entries for all possible cpus.

This is visible to the user if the kernel is booted with maxcpus=n, or
if ACPI tables have been modified to leave cpus offline, and then
checking for missing /proc/sys/kernel/sched_domain/cpu* entries.

Fix this by separating the allocataion and initialization, and adding
a flag to initialize the possible cpu entries while system booting only.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Reviewed-by: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
Tested-by: Syuuichirou Ishii <ishii.shuuichir@...fujitsu.com>
Tested-by: Tarumizu, Kohei <tarumizu.kohei@...fujitsu.com>
---
 kernel/sched/debug.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index de3de997e245..9c6637f3e21d 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -310,6 +310,7 @@ static struct ctl_table *sd_alloc_ctl_cpu_table(int cpu)
 
 static cpumask_var_t		sd_sysctl_cpus;
 static struct ctl_table_header	*sd_sysctl_header;
+static int register_sched_domain_sysctl_on_boot = 1;
 
 void register_sched_domain_sysctl(void)
 {
@@ -344,9 +345,12 @@ void register_sched_domain_sysctl(void)
 	if (!cpumask_available(sd_sysctl_cpus)) {
 		if (!alloc_cpumask_var(&sd_sysctl_cpus, GFP_KERNEL))
 			return;
+	}
 
+	if (register_sched_domain_sysctl_on_boot) {
 		/* init to possible to not have holes in @cpu_entries */
 		cpumask_copy(sd_sysctl_cpus, cpu_possible_mask);
+		register_sched_domain_sysctl_on_boot = 0;
 	}
 
 	for_each_cpu(i, sd_sysctl_cpus) {
-- 
2.20.1