linux-kernel - Re: [oliver.sang@...el.com: [cpumask] b9a7ecc71f: WARNING:at_include/linux/cpumask.h:#__is_kernel_percpu

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Date:   Tue, 11 Oct 2022 19:21:26 +0200
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>, lkp@...ts.01.org,
        lkp@...el.com, Linux Memory Management List <linux-mm@...ck.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [oliver.sang@...el.com: [cpumask] b9a7ecc71f:
 WARNING:at_include/linux/cpumask.h:#__is_kernel_percpu_address]

On Tue, Oct 11, 2022 at 10:16:01AM -0700, Yury Norov wrote:
> > Hi Yury,
> > 
> > I just wanted to report that the warning fires when doing
> > 'cat /proc/cpuinfo' on at least x86 and riscv. I don't think
> > those are false positives. I'm guessing a patch should be
> > something like the following diff. If you haven't already
> > addressed this and I'm not off in left field, then I guess
> > we should integrate it into your series.
> > 
> > Thanks,
> > drew
>  
> Hi Andrew,
> 
> Can you please send it as a patch with a description?

Will do. I'll send two patches, one for each arch.

> 
> > 
> > diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> > index 4aa8cd749441..4c5dfa230d4b 100644
> > --- a/arch/riscv/kernel/cpu.c
> > +++ b/arch/riscv/kernel/cpu.c
> > @@ -166,9 +166,12 @@ static void print_mmu(struct seq_file *f)
> >  
> >  static void *c_start(struct seq_file *m, loff_t *pos)
> >  {
> > -	*pos = cpumask_next(*pos - 1, cpu_online_mask);
> > -	if ((*pos) < nr_cpu_ids)
> > -		return (void *)(uintptr_t)(1 + *pos);
> > +	if (*pos < nr_cpu_ids) {
> > +		*pos = cpumask_next(*pos - 1, cpu_online_mask);
> > +		if ((*pos) < nr_cpu_ids)
> 
> Braces around *pos are not needed.

The braces were preexisting, but I'll drop them while indenting.

Thanks,
drew

> 
> > +			return (void *)(uintptr_t)(1 + *pos);
> > +	}
> > +
> >  	return NULL;
> >  }
> >  
> > diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> > index 099b6f0d96bd..2ea614e78e28 100644
> > --- a/arch/x86/kernel/cpu/proc.c
> > +++ b/arch/x86/kernel/cpu/proc.c
> > @@ -153,9 +153,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
> >  
> >  static void *c_start(struct seq_file *m, loff_t *pos)
> >  {
> > -	*pos = cpumask_next(*pos - 1, cpu_online_mask);
> > -	if ((*pos) < nr_cpu_ids)
> > -		return &cpu_data(*pos);
> > +	if (*pos < nr_cpu_ids) {
> > +		*pos = cpumask_next(*pos - 1, cpu_online_mask);
> > +		if ((*pos) < nr_cpu_ids)
> 
> Here too.
> 
> Thanks,
> Yury
> 
> > +			return &cpu_data(*pos);
> > +	}
> > +
> >  	return NULL;
> >  }
> >  
> > >  
> > > > I suspect that to avoid any automation noise, you should just rebase
> > > > so that the fixes come first. Otherwise we'll end up wasting a lot of
> > > > time on the noise.
> > > > 
> > > > This is not that different from introducing new buil;d-time warnings:
> > > > the things they point out need to be fixed before the warning can be
> > > > integrated, or it causes bisection problems.
> > > 
> > > OK, I'll reorder the patches. Thanks for your help.
> > >