linux-kernel - [tip:sched/core] sched/debug: Initialize sd_sysctl_cpus if !CONFIG_CPUMASK

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Date:   Mon, 4 Feb 2019 01:02:01 -0800
From:   tip-bot for Hidetoshi Seto <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     ishii.shuuichir@...fujitsu.com, torvalds@...ux-foundation.org,
        seto.hidetoshi@...fujitsu.com, tglx@...utronix.de,
        joe.lawrence@...hat.com, peterz@...radead.org,
        tarumizu.kohei@...fujitsu.com, mingo@...nel.org,
        m.mizuma@...fujitsu.com, efault@....de,
        linux-kernel@...r.kernel.org, msys.mizuma@...il.com, hpa@...or.com
Subject: [tip:sched/core] sched/debug: Initialize sd_sysctl_cpus if
 !CONFIG_CPUMASK_OFFSTACK

Commit-ID:  1ca4fa3ab604734e38e2a3000c9abf788512ffa7
Gitweb:     https://git.kernel.org/tip/1ca4fa3ab604734e38e2a3000c9abf788512ffa7
Author:     Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
AuthorDate: Tue, 29 Jan 2019 10:12:45 -0500
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 4 Feb 2019 09:13:21 +0100

sched/debug: Initialize sd_sysctl_cpus if !CONFIG_CPUMASK_OFFSTACK

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 allocation and initialization, and adding a
flag to initialize the possible CPU entries while system booting only.

Tested-by: Syuuichirou Ishii <ishii.shuuichir@...fujitsu.com>
Tested-by: Tarumizu, Kohei <tarumizu.kohei@...fujitsu.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Masayoshi Mizuma <m.mizuma@...fujitsu.com>
Acked-by: Joe Lawrence <joe.lawrence@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Masayoshi Mizuma <msys.mizuma@...il.com>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: https://lkml.kernel.org/r/20190129151245.5073-1-msys.mizuma@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/debug.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index de3de997e245..8039d62ae36e 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -315,6 +315,7 @@ void register_sched_domain_sysctl(void)
 {
 	static struct ctl_table *cpu_entries;
 	static struct ctl_table **cpu_idx;
+	static bool init_done = false;
 	char buf[32];
 	int i;
 
@@ -344,7 +345,10 @@ void register_sched_domain_sysctl(void)
 	if (!cpumask_available(sd_sysctl_cpus)) {
 		if (!alloc_cpumask_var(&sd_sysctl_cpus, GFP_KERNEL))
 			return;
+	}
 
+	if (!init_done) {
+		init_done = true;
 		/* init to possible to not have holes in @cpu_entries */
 		cpumask_copy(sd_sysctl_cpus, cpu_possible_mask);
 	}