linux-kernel - Re: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

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Date:   Wed, 01 Apr 2020 22:30:08 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org
Cc:     peterx@...hat.com, Ming Lei <ming.lei@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Luiz Capitulino <lcapitulino@...hat.com>
Subject: Re: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

Peter Xu <peterx@...hat.com> writes:
> @@ -169,8 +169,12 @@ static int __init housekeeping_isolcpus_setup(char *str)
>  			continue;
>  		}
>  
> -		pr_warn("isolcpus: Error, unknown flag\n");
> -		return 0;
> +		str = strchr(str, ',');
> +		if (str)
> +			/* Skip unknown sub-parameter */
> +			str++;
> +		else
> +			return 0;

Just looked at it again because I wanted to apply this and contrary to
last time I figured out that this is broken:

     isolcpus=nohz,domain1,3,5

is a malformatted option, but the above will make it "valid" and result
in:

     HK_FLAG_TICK and a cpumask of 3,5.

The flags are required to be is_alpha() only. So you want something like
the untested below. Hmm?

Thanks,

        tglx

8<---------------
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -149,6 +149,8 @@ static int __init housekeeping_nohz_full
 static int __init housekeeping_isolcpus_setup(char *str)
 {
 	unsigned int flags = 0;
+	char *par;
+	int len;
 
 	while (isalpha(*str)) {
 		if (!strncmp(str, "nohz,", 5)) {
@@ -169,8 +171,17 @@ static int __init housekeeping_isolcpus_
 			continue;
 		}
 
-		pr_warn("isolcpus: Error, unknown flag\n");
-		return 0;
+		/*
+		 * Skip unknown sub-parameter and validate that it is not
+		 * containing an invalid character.
+		 */
+		for (par = str, len = 0; isalpha(*str); str++, len++);
+		if (*str != ',') {
+			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 */