Messages in this thread | | | Date | Wed, 9 Nov 2016 17:37:00 -0800 | From | Stephen Boyd <> | Subject | Re: [PATCH V2 5/8] PM / OPP: Add infrastructure to manage multiple regulators |
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On 10/26, Viresh Kumar wrote: > On 25-10-16, 09:49, Stephen Boyd wrote: > > On 10/20, Viresh Kumar wrote: > > > diff --git a/drivers/base/power/opp/core.c b/drivers/base/power/opp/core.c > > > index 37fad2eb0f47..45c70ce07864 100644 > > > --- a/drivers/base/power/opp/core.c > > > +++ b/drivers/base/power/opp/core.c > > > @@ -235,21 +237,44 @@ unsigned long dev_pm_opp_get_max_volt_latency(struct device *dev) > > > return 0; > > > } > > > > > > - reg = opp_table->regulator; > > > - if (IS_ERR(reg)) { > > > + count = opp_table->regulator_count; > > > + > > > + if (!count) { > > > /* Regulator may not be required for device */ > > > rcu_read_unlock(); > > > return 0; > > > } > > > > > > - list_for_each_entry_rcu(opp, &opp_table->opp_list, node) { > > > - if (!opp->available) > > > - continue; > > > + size = count * sizeof(*regulators); > > > + regulators = kmemdup(opp_table->regulators, size, GFP_KERNEL); > > > > How do we allocate under RCU? Doesn't that spit out big warnings? > > That doesn't. I even tried enabling several locking debug config options.
Please read RCU documentation. From rcu_read_lock() function documentation:
In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it is illegal to block while in an RCU read-side critical section. In preemptible RCU implementations (TREE_PREEMPT_RCU) in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may be preempted, but explicit blocking is illegal. Finally, in preemptible RCU implementations in real-time (with -rt patchset) kernel builds, RCU read-side critical sections may be preempted and they may also block, but only when acquiring spinlocks that are subject to priority inheritance.
I suppose that in certain configurations it will warn and in others it won't. I thought lockdep would always complain though, so that's sad it doesn't. At least in some implementations of RCU rcu_read_lock() is the same as preempt_disable(), which basically means no sleeping calls like GFP_KERNEL allocations.
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