Messages in this thread | | | Date | Wed, 12 Oct 2022 15:13:25 +0200 | From | Andrew Jones <> | Subject | Re: [PATCH v2] RISC-V: Fix /proc/cpuinfo cpumask warning |
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On Wed, Oct 12, 2022 at 05:55:29AM -0700, Yury Norov wrote: > On Wed, Oct 12, 2022 at 10:29:49AM +0200, Andrew Jones wrote: > > Commit 78e5a3399421 ("cpumask: fix checking valid cpu range") has > > started issuing warnings[*] when cpu indices equal to nr_cpu_ids - 1 > > are passed to cpumask_next* functions. seq_read_iter() and cpuinfo's > > start and next seq operations implement a pattern like > > > > n = cpumask_next(n - 1, mask); > > show(n); > > while (1) { > > ++n; > > n = cpumask_next(n - 1, mask); > > if (n >= nr_cpu_ids) > > break; > > show(n); > > } > > Can you instead of sudo-code print show the real control flow? What > function hosts the infinite loop?
The function is seq_read_iter(), which is pointed out above. I'd rather not reproduce / describe more than what I've done here, as the function is large. I'd be happy for reviewers to double check my pseudocode to make sure I got it and the analysis right, though.
> > > which will issue the warning when reading /proc/cpuinfo. Ensure no > > warning is generated by validating the cpu index before calling > > cpumask_next(). > > > > [*] Warnings will only appear with DEBUG_PER_CPU_MAPS enabled. > > > > Signed-off-by: Andrew Jones <ajones@ventanamicro.com> > > Cc: Yury Norov <yury.norov@gmail.com> > > --- > > v2: > > - Got comments on the x86 equivalent patch and made the same > > changes to this one > > - Added all the information I should have in the first place > > to the commit message [Boris] > > - Changed style of fix [Boris] > > > > > > arch/riscv/kernel/cpu.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c > > index 4aa8cd749441..63138b880b92 100644 > > --- a/arch/riscv/kernel/cpu.c > > +++ b/arch/riscv/kernel/cpu.c > > @@ -166,6 +166,9 @@ static void print_mmu(struct seq_file *f) > > > > static void *c_start(struct seq_file *m, loff_t *pos) > > { > > + if (*pos >= nr_cpu_ids) > > + return NULL; > > + > > *pos = cpumask_next(*pos - 1, cpu_online_mask); > > if ((*pos) < nr_cpu_ids) > > return (void *)(uintptr_t)(1 + *pos); > > OK, as far as I understood your explanations, *pos == nr_cpu_ids > is a valid index because it's used as stop-code for traversing. > > However, you're completely silencing cpumask_check(), including > those cases where *pos > nr_cpu_ids. I suspect there's no valid > cases for it. If so, the patch should look like: > > + if (*pos == nr_cpu_ids) > + return NULL; > +
That makes sense and it's probably worth a v3. I'll wait and see if more comments roll in before sending though.
> > The same for x86 patch. > > If it comes to v3, can you send both as a series?
OK. I'll write a cover letter trying to explain that I don't expect them to both go through the same tree.
Thanks, drew
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