Messages in this thread Patch in this message | | | Date | Fri, 30 Sep 2011 14:06:25 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH RFC] stop_machine: make stop_machine safe and efficient to call early |
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On Fri, 30 Sep 2011 10:00:06 -0700 Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> On 09/30/2011 09:34 AM, Steven Rostedt wrote: > > Doesn't interrupts need to be disabled here too? As stop machine > > functions also guarantee that they will not be interrupted by > > interrupts. -- Steve > > Good point. > > J > > Make stop_machine() safe to call early in boot, before SMP has been > set up, by simply calling the callback function directly if there's > only one CPU online.
Being a trusting soul, I shall assume that you presently have or soon will have some code which requires this change?
> > ... > > --- a/kernel/stop_machine.c > +++ b/kernel/stop_machine.c > @@ -485,6 +485,17 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) > .num_threads = num_online_cpus(), > .active_cpus = cpus }; > > + if (smdata.num_threads == 1) { > + unsigned long flags; > + int ret; > + > + local_save_flags(flags); > + ret = (*fn)(data); > + local_irq_restore(flags); > + > + return ret; > + }
It is quite unobvious to readers why this code exists. Therefore, we should tell them.
Also, bug. local_save_flags() is used to read the irq flags - it does not actually disable interrupts. We want local_irq_save() here. None of these interfaces are documented and their naming system is crappy. Cause, effect.
--- a/kernel/stop_machine.c~stop_machine-make-stop_machine-safe-and-efficient-to-call-early-fix +++ a/kernel/stop_machine.c @@ -486,10 +486,14 @@ int __stop_machine(int (*fn)(void *), vo .active_cpus = cpus }; if (smdata.num_threads == 1) { + /* + * Handle the case where stop_machine() is called early in boot + * before SMP startup. + */ unsigned long flags; int ret; - local_save_flags(flags); + local_irq_save(flags); ret = (*fn)(data); local_irq_restore(flags); _
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