On 02-11-15, 11:14, Stephen Boyd wrote: > On 10/31, Viresh Kumar wrote: > > On 30-10-15, 10:06, Stephen Boyd wrote: > > > On 10/30, Viresh Kumar wrote: > > > > dev_opp_list_lock is used everywhere to protect device and OPP lists, > > > > but dev_pm_opp_set_sharing_cpus() is missed somehow. And instead we used > > > > rcu-lock, which wouldn't help here as we are adding a new list_dev. > > > > > > > > This also fixes a problem where we have called kzalloc(..., GFP_KERNEL) > > > > from within rcu-lock, which isn't allowed as kzalloc can sleep when > > > > called with GFP_KERNEL. > > > > > > Care to share the splat here? > > > > I don't know what is wrong (or right) with my exynos 5250 board, but I > > didn't got any splat here even with the right config options (yes I > > should have mentioned that earlier). I have seen this at other times > > as well, while we were running after some cpufreq traces.. > > > > But, the case in hand is pretty straight forward and Mike T. did get a > > splat as that's what he told me. We are calling a sleep-able function > > from rcu_lock and that's obviously wrong. > > That's slightly concerning. Given that the bug is so straight > forward but we can't reproduce it doesn't instill a lot of > confidence that the patch is correct.
I have asked Mike to provide the splat he got and test the new patch to see if it is fixed or not. > > > > diff --git a/drivers/base/power/opp/cpu.c b/drivers/base/power/opp/cpu.c > > > > index 7654c5606307..91f15b2e25ee 100644 > > > > --- a/drivers/base/power/opp/cpu.c > > > > +++ b/drivers/base/power/opp/cpu.c > > > > @@ -124,12 +124,12 @@ int dev_pm_opp_set_sharing_cpus(struct device > > > > *cpu_dev, cpumask_var_t cpumask) > > > > struct device *dev; > > > > int cpu, ret = 0; > > > > > > > > - rcu_read_lock(); > > > > + mutex_lock(&dev_opp_list_lock); > > > > > > > > dev_opp = _find_device_opp(cpu_dev); > > > > > > So does _find_device_opp() need to be called with rcu_read_lock() > > > held or not? The comment above the function makes it sound like > > > we need RCU, but we don't do that here anymore. > > > > That is more for the readers, as this function is going to return a > > pointer to the device OPP, and to make sure it isn't freed behind > > their back, they need to take the RCU lock. > > > > There are other writer code paths as well, like add-opp, where we just > > take the mutex as there can't be anything stronger than that :) > > > > Agreed, but the comment above the function is misleading. We > should correct that comment and/or add the lockdep checks to the > function like we have elsewhere in this file. Will do. -- viresh -- 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/