On Friday, August 30, 2013 08:26:34 PM Daniel Fu wrote: > X-NVConfidentiality: public > > In SMP, When doing the cpuidle driver registration. There maybe only 1 cpu > have register cpuidle(CPU0), > but In the process of registration cpuidle driver, the scheduler maybe > schedule the process to the other CPU (eg. CPU0 have heay load, migrate to > CPU1) > cpuidle_get_driver() --> get_cpu() , will get CPU1, if CPU1 didn't register > cpuidle driver, Will get NULL. > > I know we should prevent the registration migrate to the other CPU, but we > should check drv before add refcount to prevent kernel panic at least, Right?
Well, cpuidle_driver_ref() has only one caller, which is not the registration. However, the caller apparently assumes that that function may return NULL and cpuidle_driver_unref() check drv against NULL too, so cpuidle_driver_ref() should do that either. Did you see that problem in testing or just through code inspection? Rafael > -----Original Message----- > From: Rafael J. Wysocki [mailto:r...@sisk.pl] > Sent: 2013年8月30日 20:01 > To: Daniel Fu > Cc: daniel.lezc...@linaro.org; linux...@vger.kernel.org; > linux-kernel@vger.kernel.org; Johnny Qiu > Subject: Re: [PATCH] cpuidle: Check cpuidle driver before add refcount > > On Friday, August 30, 2013 07:48:22 PM Daniel Fu wrote: > > If the current CPU has no cpuidle driver, drv will be NULL. > > Check if we get drv successfully before add refount to prevent Kernel > > panic. > > What is the actual scenario that may lead to this panic? > > Rafael > > > > Signed-off-by: Daniel Fu <dan...@nvidia.com> > > --- > > drivers/cpuidle/driver.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c index > > 3ac499d..6e11701 100644 > > --- a/drivers/cpuidle/driver.c > > +++ b/drivers/cpuidle/driver.c > > @@ -331,7 +331,8 @@ struct cpuidle_driver *cpuidle_driver_ref(void) > > spin_lock(&cpuidle_driver_lock); > > > > drv = cpuidle_get_driver(); > > - drv->refcnt++; > > + if (drv) > > + drv->refcnt++; > > > > spin_unlock(&cpuidle_driver_lock); > > return drv; > > > -- > I speak only for myself. > Rafael J. Wysocki, Intel Open Source Technology Center. > -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
