linux-kernel - [PATCH] Fix isocpus's param handling when CPUMASK

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Message-Id: <20171015131820.7173-1-rakib.mullick@gmail.com>
Date:   Sun, 15 Oct 2017 19:18:20 +0600
From:   Rakib Mullick <rakib.mullick@...il.com>
To:     peterz@...radead.org, mingo@...nel.org
Cc:     mka@...omium.org, longman@...hat.com, adobriyan@...il.com,
        tglx@...utronix.de, akpm@...ux-foundation.org, tj@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] Fix isocpus's param handling when CPUMASK_OFFSTACK=n.

 cpulist_parse() uses nr_cpumask_bits as limit to parse the
passed buffer from kernel commandline. What nr_cpumask_bits
represents varies depends upon CONFIG_CPUMASK_OFFSTACK option.
If CONFIG_CPUMASK_OFFSTACK=n, then nr_cpumask_bits is same as
NR_CPUS, which might not represent the # of cpus really exist
(default 64). So, there's a chance of gap between nr_cpu_ids
and NR_CPUS, which ultimately lead towards invalid cpulist_parse()
operation. For example, if isolcpus=9 is passed on a 8 cpu
system (CONFIG_CPUMASK_OFFSTACK=n) it doesn't show the error
that it suppose to.

This patch fixes this issue by effectively find out the last
cpu of the passed isolcpus list and checking it with nr_cpu_ids.
Also, fixes the error message where the nr_cpu_ids should be
nr_cpu_ids-1, since the cpu numbering starts from 0.

Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
---
 include/linux/cpumask.h | 16 ++++++++++++++++
 kernel/sched/topology.c |  8 +++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 2404ad2..f9a7c9b 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -130,6 +130,11 @@ static inline unsigned int cpumask_first(const struct cpumask *srcp)
 	return 0;
 }
 
+static inline unsigned int cpumask_last(const struct cpumask *srcp)
+{
+	return 0;
+}
+
 /* Valid inputs for n are -1 and 0. */
 static inline unsigned int cpumask_next(int n, const struct cpumask *srcp)
 {
@@ -179,6 +184,17 @@ static inline unsigned int cpumask_first(const struct cpumask *srcp)
 }
 
 /**
+ * cpumask_last - get the last cpu in a cpumask
+ * @srcp:	- the cpumask pointer
+ *
+ * Returns	>= nr_cpumask_bits if no cpus set.
+ */
+static inline unsigned int cpumask_last(const struct cpumask *srcp)
+{
+	return find_last_bit(cpumask_bits(srcp), nr_cpumask_bits);
+}
+
+/**
  * cpumask_next - get the next cpu in a cpumask
  * @n: the cpu prior to the place to search (ie. return will be > @n)
  * @srcp: the cpumask pointer
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 1b0b4fb..55b5e09 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -452,12 +452,14 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 /* Setup the mask of CPUs configured for isolated domains */
 static int __init isolated_cpu_setup(char *str)
 {
-	int ret;
+	int ret, lastcpu;
 
 	alloc_bootmem_cpumask_var(&cpu_isolated_map);
 	ret = cpulist_parse(str, cpu_isolated_map);
-	if (ret) {
-		pr_err("sched: Error, all isolcpus= values must be between 0 and %d\n", nr_cpu_ids);
+	lastcpu = cpumask_last(cpu_isolated_map);
+	if (ret || lastcpu >= nr_cpu_ids) {
+		pr_err("sched: Error, all isolcpus= values must be between 0 and %d\n",
+				nr_cpu_ids-1);
 		return 0;
 	}
 	return 1;
-- 
2.9.3