Commit 3662daf0 authored Apr 03, 2020 by Peter Xu Committed by Thomas Gleixner Apr 15, 2020

sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters



The "isolcpus=" parameter allows sub-parameters before the cpulist is
specified, and if the parser detects an unknown sub-parameters the whole
parameter will be ignored.

This design is incompatible with itself when new sub-parameters are added.
An older kernel will not recognize the new sub-parameter and will
invalidate the whole parameter so the CPU isolation will not take
effect. It emits a warning:

    isolcpus: Error, unknown flag

The better and compatible way is to allow "isolcpus=" to skip unknown
sub-parameters, so that even if new sub-parameters are added an older
kernel will still be able to behave as usual even if with the new
sub-parameter specified on the command line.

Ideally this should have been there when the first sub-parameter for
"isolcpus=" was introduced.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200403223517.406353-1-peterx@redhat.com

parent 8f3d9f35

kernel/sched/isolation.c

+19 −2

Original line number	Diff line number	Diff line
		@@ -149,6 +149,9 @@ __setup("nohz_full=", housekeeping_nohz_full_setup);
		static int __init housekeeping_isolcpus_setup(char *str)
		{
		unsigned int flags = 0;
		bool illegal = false;
		char *par;
		int len;

		while (isalpha(*str)) {
		if (!strncmp(str, "nohz,", 5)) {
		@@ -169,10 +172,24 @@ static int __init housekeeping_isolcpus_setup(char *str)
		continue;
		}

		pr_warn("isolcpus: Error, unknown flag\n");
		/*
		* Skip unknown sub-parameter and validate that it is not
		* containing an invalid character.
		*/
		for (par = str, len = 0; str && str != ','; str++, len++) {
		if (!isalpha(str) && str != '_')
		illegal = true;
		}

		if (illegal) {
		pr_warn("isolcpus: Invalid flag %.*s\n", len, par);
		return 0;
		}

		pr_info("isolcpus: Skipped unknown flag %.*s\n", len, par);
		str++;
		}

		/* Default behaviour for isolcpus without flags */
		if (!flags)
		flags \|= HK_FLAG_DOMAIN;

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