[PATCH 4.14 086/121] sched/debug: Initialize sd_sysctl_cpus if !CONFIG_CPUMASK_OFFSTACK

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 1ca4fa3ab604734e38e2a3000c9abf788512ffa7 ]

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@xxxxxxxxxxxxxx>
Tested-by: Tarumizu, Kohei <tarumizu.kohei@xxxxxxxxxxxxxx>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
Acked-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Masayoshi Mizuma <msys.mizuma@xxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190129151245.5073-1-msys.mizuma@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/sched/debug.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 2f93e4a2d9f6..187c04a34ba1 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -339,6 +339,7 @@ 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;
 
@@ -368,7 +369,10 @@ 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);
 	}
-- 
2.19.1