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SubjectRe: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters
On Wed, Apr 01, 2020 at 10:30:08PM +0200, Thomas Gleixner wrote:
> Peter Xu <peterx@redhat.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.

I would think this is no worse than applying nothing - I read the
first "isalpha()" check as something like "the subparameter's first
character must not be a digit", so to differenciate with the cpu list.
If we keep this, we can still have subparams like "double-word".

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

I'm fine with it, however note that...

>
> 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);

... this will dump "isolcpus: Invalid flag domain1,3,5", is this what
we wanted? Maybe only dumps "domain1"?

For me so far I would still prefer the original one, giving more
freedom to the future params and the patch is also a bit easier (but I
definitely like the pr_warn when there's unknown subparams). But just
let me know your preference and I'll follow yours when repost.

Thanks,

> + return 0;
> + }
> + pr_info("isolcpus: Skipped unknown flag %*s\n", len, par);
> + str++;
> }
>
> /* Default behaviour for isolcpus without flags */
>

--
Peter Xu

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