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

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Message-Id: <20171023130154.9050-1-rakib.mullick@gmail.com>
Date:   Mon, 23 Oct 2017 19:01:54 +0600
From:   Rakib Mullick <rakib.mullick@...il.com>
To:     mingo@...nel.org
Cc:     peterz@...radead.org, 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.


> On Mon, Oct 23, 2017 at 5:50 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
>> * Rakib Mullick <rakib.mullick@...il.com> wrote:
>> +/**
>> + * cpumask_last - get the last cpu in a cpumask
>
> Please capitalize 'CPU' properly in documentation.
>
OK.
>> +     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 %u\n", nr_cpu_ids);
>> +     lastcpu = cpumask_last(cpu_isolated_map);
>> +     if (ret || lastcpu >= nr_cpu_ids) {
>
> Any reason why 'lastcpu' has to be introduced - why not just use cpumask_last()
> directly in the condition? It looks obvious enough of a pattern.
Thought it reflects what we're doing here, but yes, actually it's redundant.

>> +             pr_err("sched: Error, all isolcpus= values must be between 0 and %u\n",
>> +                             nr_cpu_ids-1);
>
> Please don't break the line mindlessly just due to checkpatch complaining - it
> makes the code less readable.
>
Yes, right, mindlessly followed what checkpatch was complaining.

Please see the following patch, with changes made based on your review and
patched up against -rc6.

Thanks,
Rakib
---

[PATCH](v1) 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.

Changes since v0 (Ingo):
	* use cpumask_last() directly into the condition.
	* use CPU rather cpu in documentation
	* undo line break

Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
---
 include/linux/cpumask.h | 16 ++++++++++++++++
 kernel/sched/topology.c |  4 ++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index cd415b7..63661de 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)
 {
@@ -178,6 +183,17 @@ static inline unsigned int cpumask_first(const struct cpumask *srcp)
 	return find_first_bit(cpumask_bits(srcp), nr_cpumask_bits);
 }
 
+/**
+ * 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);
+}
+
 unsigned int cpumask_next(int n, const struct cpumask *srcp);
 
 /**
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index f1cf4f3..060cee5 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -470,8 +470,8 @@ static int __init isolated_cpu_setup(char *str)
 
 	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 %u\n", nr_cpu_ids);
+	if (ret || cpumask_last(cpu_isolated_map) >= nr_cpu_ids) {
+		pr_err("sched: Error, all isolcpus= values must be between 0 and %u\n", nr_cpu_ids-1);
 		return 0;
 	}
 	return 1;
-- 
2.9.3