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 19:09:49 +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 Sat, Oct 01, 2022 at 10:16:36AM -0700, Yury Norov wrote:
> On Sat, Oct 01, 2022 at 09:20:53AM -0700, Linus Torvalds wrote:
> > On Fri, Sep 30, 2022 at 6:51 PM Yury Norov <yury.norov@...il.com> wrote:
> > >
> > > The commit  b9a7ecc71fe582e ("cpumask: fix checking valid cpu range")
> > > fixes broken cpumask_check(), which for now doesn't warn user when it
> > > should. After the fix, I observed many false-positive warnings which
> > > were addressed in the following patches.
> > 
> > Are all the false positives fixed?
> 
> I build-tested on x86_64 and arm64. All fixed except for those
> generated by cpumask_next_wrap(). And I'm not even sure they
> are false positives.
> 
> This is what I'm working on right now. Hope moving it in next
> merge window.

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


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)
+			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)
+			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.
>