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SubjectRe: [PATCH v3] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters
Ping - Thomas, do you think this version is ok to you?

This has missed 5.7 already, am I right?

Thanks,

On Fri, Apr 03, 2020 at 06:35:17PM -0400, Peter Xu wrote:
> The "isolcpus=" parameter allows sub-parameters to exist before the
> cpulist is specified, and if it sees unknown sub-parameters the whole
> parameter will be ignored. This design is incompatible with itself
> when we add more sub-parameters to "isolcpus=", because the old
> kernels will not recognize the new "isolcpus=" sub-parameters, then it
> will invalidate the whole parameter so the CPU isolation will not
> really take effect if we start to use the new sub-parameters while
> later we reboot into an old kernel. Instead we will see this when
> booting the old kernel:
>
> isolcpus: Error, unknown flag
>
> The better and compatible way is to allow "isolcpus=" to skip unknown
> sub-parameters, so that even if we add new sub-parameters to it the
> old kernel will still be able to behave as usual even if with the new
> sub-parameter is specified.
>
> Ideally this patch should be there when we introduce the first
> sub-parameter for "isolcpus=", so it's already a bit late. However
> late is better than nothing.
>
> CC: Ming Lei <ming.lei@redhat.com>
> CC: Ingo Molnar <mingo@redhat.com>
> CC: Peter Zijlstra <peterz@infradead.org>
> CC: Juri Lelli <juri.lelli@redhat.com>
> CC: Luiz Capitulino <lcapitulino@redhat.com>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> v3:
> - add brackets for for loop
> - move "illegal" a bit higher, which may look tiny bit nicer
> - also allow '_'
> v2:
> - only allow isalpha() for sub-parameters [tglx]
> ---
> kernel/sched/isolation.c | 21 +++++++++++++++++++--
> 1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 008d6ac2342b..808244f3ddd9 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -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)) {
> @@ -169,8 +172,22 @@ static int __init housekeeping_isolcpus_setup(char *str)
> 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; *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 */
> --
> 2.24.1
>

--
Peter Xu

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