Commit e22cdc3f authored Oct 23, 2017 by Rakib Mullick Committed by Ingo Molnar Oct 24, 2017

sched/isolcpus: Fix "isolcpus=" boot parameter handling when !CONFIG_CPUMASK_OFFSTACK



cpulist_parse() uses nr_cpumask_bits as a limit to parse the
passed buffer from kernel commandline. What nr_cpumask_bits
represents varies depending upon the CONFIG_CPUMASK_OFFSTACK option:

 - If CONFIG_CPUMASK_OFFSTACK=n, then nr_cpumask_bits is the same as
   NR_CPUS, which might not represent the # of CPUs that really exist
   (default 64). So, there's a chance of a gap between nr_cpu_ids
   and NR_CPUS, which ultimately lead towards invalid cpulist_parse()
   operation. For example, if isolcpus=9 is passed on an 8 cpu
   system (CONFIG_CPUMASK_OFFSTACK=n) it doesn't show the error
   that it's supposed to.

This patch fixes this bug by finding the last CPU of the passed
isolcpus= list and checking it against nr_cpu_ids.

It also fixes the error message where the nr_cpu_ids should be
nr_cpu_ids-1, since CPU numbering starts from 0.

Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: adobriyan@gmail.com
Cc: akpm@linux-foundation.org
Cc: longman@redhat.com
Cc: mka@chromium.org
Cc: tj@kernel.org
Link: http://lkml.kernel.org/r/20171023130154.9050-1-rakib.mullick@gmail.com


[ Enhanced the changelog and the kernel message. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

 include/linux/cpumask.h |   16 ++++++++++++++++
 kernel/sched/topology.c |    4 ++--
 2 files changed, 18 insertions(+), 2 deletions(-)

parent 6be53520

include/linux/cpumask.h

+16 −0

Original line number	Diff line number	Diff line
		@@ -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);

		/**

kernel/sched/topology.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -476,8 +476,8 @@ 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 - ignoring them.\n", nr_cpu_ids-1);
		return 0;
		}
		return 1;

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