[PATCH] PM / OPP: Protect updates to list_dev with mutex

[PATCH] PM / OPP: Protect updates to list_dev with mutex

[Viresh Kumar]

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.

With CONFIG_DEBUG_ATOMIC_SLEEP set, we will see the caller vomiting.

Fixes: 8d4d4e98acd6 ("PM / OPP: Add helpers for initializing CPU OPPs")
Reported-by: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
Mike: Can you please verify if this fixes it for you..

 drivers/base/power/opp/core.c | 2 +-
 drivers/base/power/opp/cpu.c  | 8 ++++----
 drivers/base/power/opp/opp.h  | 3 +++
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/base/power/opp/core.c b/drivers/base/power/opp/core.c
index d5c1149ff123..69f83cbe37b2 100644
--- a/drivers/base/power/opp/core.c
+++ b/drivers/base/power/opp/core.c
@@ -27,7 +27,7 @@
  */
 static LIST_HEAD(dev_opp_list);
 /* Lock to allow exclusive modification to the device and opp lists */
-static DEFINE_MUTEX(dev_opp_list_lock);
+DEFINE_MUTEX(dev_opp_list_lock);
 
 #define opp_rcu_lockdep_assert()					\
 do {									\
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);
 	if (IS_ERR(dev_opp)) {
 		ret = -EINVAL;
-		goto out_rcu_read_unlock;
+		goto unlock;
 	}
 
 	for_each_cpu(cpu, cpumask) {
@@ -150,8 +150,8 @@ int dev_pm_opp_set_sharing_cpus(struct device *cpu_dev, cpumask_var_t cpumask)
 			continue;
 		}
 	}
-out_rcu_read_unlock:
-	rcu_read_unlock();
+unlock:
+	mutex_unlock(&dev_opp_list_lock);
 
 	return 0;
 }
diff --git a/drivers/base/power/opp/opp.h b/drivers/base/power/opp/opp.h
index dcb38f78dae4..7366b2aa8997 100644
--- a/drivers/base/power/opp/opp.h
+++ b/drivers/base/power/opp/opp.h
@@ -21,6 +21,9 @@
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
 
+/* Lock to allow exclusive modification to the device and opp lists */
+extern struct mutex dev_opp_list_lock;
+
 /*
  * Internal data structure organization with the OPP layer library is as
  * follows:
-- 
2.6.2.198.g614a2ac

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Dan Carpenter]

On Fri, Oct 30, 2015 at 05:26:06PM +0530, Viresh Kumar wrote:
> --- 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);
>  	if (IS_ERR(dev_opp)) {
>  		ret = -EINVAL;
> -		goto out_rcu_read_unlock;
> +		goto unlock;
>  	}
>  
>  	for_each_cpu(cpu, cpumask) {
> @@ -150,8 +150,8 @@ int dev_pm_opp_set_sharing_cpus(struct device *cpu_dev, cpumask_var_t cpumask)
>  			continue;
>  		}
>  	}
> -out_rcu_read_unlock:
> -	rcu_read_unlock();
> +unlock:
> +	mutex_unlock(&dev_opp_list_lock);
>  
>  	return 0;

Not introduced by your patch, but this should be "return ret;"

regards,
dan carpenter

[PATCH] PM / OPP: Propagate error properly from dev_pm_opp_set_sharing_cpus()

[Viresh Kumar]

We are returning 0 even in case of errors, fix it.

Fixes: 8d4d4e98acd6 ("PM / OPP: Add helpers for initializing CPU OPPs")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/base/power/opp/cpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/power/opp/cpu.c b/drivers/base/power/opp/cpu.c
index 91f15b2e25ee..2122543e769d 100644
--- a/drivers/base/power/opp/cpu.c
+++ b/drivers/base/power/opp/cpu.c
@@ -153,7 +153,7 @@ int dev_pm_opp_set_sharing_cpus(struct device *cpu_dev, cpumask_var_t cpumask)
 unlock:
 	mutex_unlock(&dev_opp_list_lock);
 
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(dev_pm_opp_set_sharing_cpus);
 
-- 
2.6.2.198.g614a2ac

Re: [PATCH] PM / OPP: Propagate error properly from dev_pm_opp_set_sharing_cpus()

[Stephen Boyd]

On 10/30, Viresh Kumar wrote:
> We are returning 0 even in case of errors, fix it.
> 
> Fixes: 8d4d4e98acd6 ("PM / OPP: Add helpers for initializing CPU OPPs")
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---

Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Stephen Boyd]

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?

> 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.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Viresh Kumar]

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.

> > 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 :)

-- 
viresh

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Stephen Boyd]

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.

> 
> > > 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.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Viresh Kumar]

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

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Viresh Kumar]

On 02-11-15, 11:14, Stephen Boyd wrote:
> On 10/31, Viresh Kumar wrote:
> > 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.

Good that I spent some time debugging why I wasn't able to hit the
lockdep. And that's because by default CONFIG_PREEMPT_RCU was
selected on exynos and so the dummy function was getting enabled, and
so no WARN.

#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
static inline void rcu_preempt_sleep_check(void)
{
	RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
			 "Illegal context switch in RCU read-side critical section");
}
#else /* #ifdef CONFIG_PROVE_RCU */
static inline void rcu_preempt_sleep_check(void)
{
}
#endif /* #else #ifdef CONFIG_PROVE_RCU */

Whereas for omap, that's not the case :)

So, with some config changes, I was able to hit the lockdep :)

And just to confirm, they got fixed by the $Subject patch :)

-- 
viresh

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Michael Turquette]

Quoting Viresh Kumar (2015-10-30 19:14:09)
> 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.

Splat:

[    2.461883] ===============================
[    2.466278] [ INFO: suspicious RCU usage. ]
[    2.470703] 4.3.0-rc7-00004-g7f16d90-dirty #11 Not tainted
[    2.476501] -------------------------------
[    2.480895] include/linux/rcupdate.h:578 Illegal context switch in RCU read-side critical section!
[    2.490325]
[    2.490325] other info that might help us debug this:
[    2.490325]
[    2.498779]
[    2.498779] rcu_scheduler_active = 1, debug_locks = 1
[    2.505645] 4 locks held by swapper/0/1:
[    2.509796]  #0:  (&dev->mutex){......}, at: [<c0678e1c>] __device_attach+0x20/0x10c
[    2.518066]  #1:  (cpu_hotplug.lock){++++++}, at: [<c024c204>] get_online_cpus+0x40/0xb0
[    2.526672]  #2:  (subsys mutex#5){+.+.+.}, at: [<c0677900>] subsys_interface_register+0x44/0xdc
[    2.535980]  #3:  (rcu_read_lock){......}, at: [<c0687bc8>] set_cpus_sharing_opps+0x0/0x1d4
[    2.544860]
[    2.544860] stack backtrace:
[    2.549499] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.3.0-rc7-00004-g7f16d90-dirty #11
[    2.558013] Hardware name: Generic OMAP4 (Flattened Device Tree)
[    2.564361] [<c0219c34>] (unwind_backtrace) from [<c0215228>] (show_stack+0x10/0x14)
[    2.572570] [<c0215228>] (show_stack) from [<c04c2af0>] (dump_stack+0x98/0xc0)
[    2.580200] [<c04c2af0>] (dump_stack) from [<c0270a84>] (___might_sleep+0x24c/0x298)
[    2.588378] [<c0270a84>] (___might_sleep) from [<c0328ccc>] (kmem_cache_alloc+0xe8/0x164)
[    2.597015] [<c0328ccc>] (kmem_cache_alloc) from [<c068706c>] (_add_list_dev+0x20/0x48)
[    2.605468] [<c068706c>] (_add_list_dev) from [<c0687c98>] (set_cpus_sharing_opps+0xd0/0x1d4)
[    2.614471] [<c0687c98>] (set_cpus_sharing_opps) from [<c086b9b4>] (cpufreq_init+0x4cc/0x62c)
[    2.623474] [<c086b9b4>] (cpufreq_init) from [<c0867780>] (cpufreq_online+0xc8/0x704)
[    2.631713] [<c0867780>] (cpufreq_online) from [<c0677954>] (subsys_interface_register+0x98/0xdc)
[    2.641082] [<c0677954>] (subsys_interface_register) from [<c08682b4>] (cpufreq_register_driver+0x110/0x17c)
[    2.651458] [<c08682b4>] (cpufreq_register_driver) from [<c086bb74>] (dt_cpufreq_probe+0x60/0x8c)
[    2.660827] [<c086bb74>] (dt_cpufreq_probe) from [<c067a9f8>] (platform_drv_probe+0x44/0xa4)
[    2.669708] [<c067a9f8>] (platform_drv_probe) from [<c0679134>] (driver_probe_device+0x208/0x2f4)
[    2.679077] [<c0679134>] (driver_probe_device) from [<c0677630>] (bus_for_each_drv+0x60/0x94)
[    2.688079] [<c0677630>] (bus_for_each_drv) from [<c0678ea4>] (__device_attach+0xa8/0x10c)
[    2.696777] [<c0678ea4>] (__device_attach) from [<c0678584>] (bus_probe_device+0x88/0x90)
[    2.705413] [<c0678584>] (bus_probe_device) from [<c0676934>] (device_add+0x3e8/0x574)
[    2.713775] [<c0676934>] (device_add) from [<c067a70c>] (platform_device_add+0xb4/0x20c)
[    2.722320] [<c067a70c>] (platform_device_add) from [<c067af70>] (platform_device_register_full+0xc4/0xe8)
[    2.732482] [<c067af70>] (platform_device_register_full) from [<c0eaccf0>] (omap2_common_pm_late_init+0x108/0x114)
[    2.743377] [<c0eaccf0>] (omap2_common_pm_late_init) from [<c0ea9f18>] (omap_common_late_init+0xc/0x14)
[    2.753295] [<c0ea9f18>] (omap_common_late_init) from [<c0eaa3d8>] (omap4430_init_late+0x8/0x14)
[    2.762542] [<c0eaa3d8>] (omap4430_init_late) from [<c0e9e8cc>] (init_machine_late+0x20/0x94)
[    2.771545] [<c0e9e8cc>] (init_machine_late) from [<c020ad50>] (do_one_initcall+0x8c/0x1d8)
[    2.780395] [<c020ad50>] (do_one_initcall) from [<c0e9ce08>] (kernel_init_freeable+0x158/0x1f8)
[    2.789581] [<c0e9ce08>] (kernel_init_freeable) from [<c0a4ac04>] (kernel_init+0xc/0xe8)
[    2.798126] [<c0a4ac04>] (kernel_init) from [<c0210dd0>] (ret_from_fork+0x14/0x24)

Regards,
Mike

> 
> > > 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 :)
> 
> -- 
> viresh

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Viresh Kumar]

On 04-11-15, 02:22, Michael Turquette wrote:
> Splat:
> 

Thanks, but I also need your Tested-by :)

-- 
viresh

Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

[Stephen Boyd]

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.
> 
> With CONFIG_DEBUG_ATOMIC_SLEEP set, we will see the caller vomiting.
> 
> Fixes: 8d4d4e98acd6 ("PM / OPP: Add helpers for initializing CPU OPPs")
> Reported-by: Michael Turquette <mturquette@baylibre.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---

Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>

I assume some other patch will come to fix the comment and/or add
the lockdep check.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project