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Date: Thu, 2 Apr 2020 21:15:59 -0400 From: Peter Xu <peterx@...hat.com> To: linux-kernel@...r.kernel.org Cc: 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>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH v2] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters On Thu, Apr 02, 2020 at 10:59:29AM -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@...hat.com> > CC: Ingo Molnar <mingo@...hat.com> > CC: Peter Zijlstra <peterz@...radead.org> > CC: Juri Lelli <juri.lelli@...hat.com> > CC: Luiz Capitulino <lcapitulino@...hat.com> > Suggested-by: Thomas Gleixner <tglx@...utronix.de> > Signed-off-by: Peter Xu <peterx@...hat.com> > --- > v2: > - only allow isalpha() for sub-parameters [tglx] > --- > kernel/sched/isolation.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c > index 008d6ac2342b..c2e8b4a778d6 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; > + char *par; > + int len; > + bool illegal = false; > > while (isalpha(*str)) { > if (!strncmp(str, "nohz,", 5)) { > @@ -169,8 +172,21 @@ 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)) > + 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++; > } I just noticed this is still problematic if we want to mark this as stable, because "managed_irq" violate the "isalpha()" rule already... It means even if we apply this patch to the stable trees it'll still think managed_irq as illegal and ignore the whole isolcpus=. Thomas, do you want me to repost a v3 as v1 plus some pr_warn()s? Thanks, -- Peter Xu
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