Re: 2.6.29-rc1 does not boot

Ingo Molnar
2009-01-12T18:56:19Z

* Mike Travis <travis@sgi.com> wrote:

> Ingo Molnar wrote:
> > * Mike Travis <travis@sgi.com> wrote:
> ...
> >> Rusty - any ideas on how to avoid these clashes with the
> >> get_online_cpus() call in work_on_cpu()? Or something else to indicate
> >> to lockdep that the circular lock dependency is ok (as you mentioned
> >> before)?
> >
> > I've queued up the revert below, please check the commit message whether
> > you agree with the analysis.
> >
> > Mike, could you also check any other patches where you add work_on_cpu()
> > usage to make sure we dont have similar mishaps? work_on_cpu() seems
> > completely unsuited for any sort of set_cpus_allowed() replacement ...
> >
> > Ingo
>
> Yes, I'll do that now. With the resume feature also calling these functions,
> I'm even less comfortable with it.
>
> Shall I resurrect the 2nd cpumask in the task struct from my original patches,
> (and one that akpm also suggested more than a year ago)?
>
> Basically, it looks like this:
>
> --- linux-2.6-for-ingo.orig/include/linux/sched.h 2009-01-11 10:43:19.000000000 -0800
> +++ linux-2.6-for-ingo/include/linux/sched.h 2009-01-12 09:45:02.871247038 -0800
> @@ -1132,6 +1132,7 @@ struct task_struct {
>
> unsigned int policy;
> cpumask_t cpus_allowed;
> + cpumask_t save_cpus_allowed;
>
> --- linux-2.6-for-ingo.orig/arch/x86/kernel/microcode_core.c 2009-01-12 09:05:36.000000000 -0800
> +++ linux-2.6-for-ingo/arch/x86/kernel/microcode_core.c 2009-01-12 09:49:19.315276144 -0800
> @@ -110,11 +110,10 @@ EXPORT_SYMBOL_GPL(ucode_cpu_info);
> #ifdef CONFIG_MICROCODE_OLD_INTERFACE
> static int do_microcode_update(const void __user *buf, size_t size)
> {
> - cpumask_t old;
> int error = 0;
> int cpu;
>
> - old = current->cpus_allowed;
> + cpumask_copy(&current->save_cpus_allowed, &current->cpus_allowed);
>
> for_each_online_cpu(cpu) {
> struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
> @@ -122,7 +121,7 @@ static int do_microcode_update(const voi
> if (!uci->valid)
> continue;
>
> - set_cpus_allowed_ptr(current, &cpumask_of_cpu(cpu));
> + set_cpus_allowed_ptr(current, cpumask_of(cpu));
> error = microcode_ops->request_microcode_user(cpu, buf, size);
> if (error < 0)
> goto out;
> @@ -130,7 +129,7 @@ static int do_microcode_update(const voi
> microcode_ops->apply_microcode(cpu);
> }
> out:
> - set_cpus_allowed_ptr(current, &old);
> + set_cpus_allowed_ptr(current, &current->save_cpus_allowed);
> return error;
> }
>
> The primary concern is that there is only one temp, so I had also put in
> a warning if it was already in use. But the scope of where it's used is
> very short-lived, so I don't know if a preempt_disable() is required,
> but it seems the safe thing to do.

that's rather fragile. Fix work_on_cpu() instead? Why does it need to take
the CPU-hotplug lock?

Ingo