Messages in this thread | | | Date | Mon, 29 Apr 2013 17:51:46 -0700 | From | John Stultz <> | Subject | Re: [patch 04/15] clocksource: Add module refcount |
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On 04/25/2013 01:31 PM, Thomas Gleixner wrote: > Add a module refcount, so the current clocksource cannot be removed > unconditionally. > > Signed-off-by: Thomas Gleixner<tglx@linutronix.de> > --- > include/linux/clocksource.h | 3 +++ > kernel/time/timekeeping.c | 15 ++++++++++----- > 2 files changed, 13 insertions(+), 5 deletions(-) > > Index: tip/include/linux/clocksource.h > =================================================================== > --- tip.orig/include/linux/clocksource.h > +++ tip/include/linux/clocksource.h > @@ -21,6 +21,7 @@ > /* clocksource cycle base type */ > typedef u64 cycle_t; > struct clocksource; > +struct module; > > #ifdef CONFIG_ARCH_CLOCKSOURCE_DATA > #include <asm/clocksource.h> > @@ -162,6 +163,7 @@ extern u64 timecounter_cyc2time(struct t > * @suspend: suspend function for the clocksource, if necessary > * @resume: resume function for the clocksource, if necessary > * @cycle_last: most recent cycle counter value seen by ::read() > + * @owner: module reference > */ > struct clocksource { > /* > @@ -195,6 +197,7 @@ struct clocksource { > cycle_t cs_last; > cycle_t wd_last; > #endif > + struct module *owner;
Maybe could you add a comment about who is expected to set the owner ptr?
> } ____cacheline_aligned; > > /* > Index: tip/kernel/time/timekeeping.c > =================================================================== > --- tip.orig/kernel/time/timekeeping.c > +++ tip/kernel/time/timekeeping.c > @@ -627,11 +627,16 @@ static int change_clocksource(void *data > write_seqcount_begin(&timekeeper_seq); > > timekeeping_forward_now(tk); > - if (!new->enable || new->enable(new) == 0) { > - old = tk->clock; > - tk_setup_internals(tk, new); > - if (old->disable) > - old->disable(old); > + if (try_module_get(new->owner)) {
Hrm.. So this works, but the interface is a bit non-intuitive, since without looking up try_module_get() I'd be surprised that this would succeed if the owner ptr is null. Maybe deserves a comment?
> + if (!new->enable || new->enable(new) == 0) { > + old = tk->clock; > + tk_setup_internals(tk, new); > + if (old->disable) > + old->disable(old); > + module_put(old->owner); > + } else { > + module_put(new->owner); > + } > } > timekeeping_update(tk, true, true); >
thanks -john
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