[PATCH] opp: Reduce the size of critical section in _opp_table_kref_release()

[PATCH] opp: Reduce the size of critical section in _opp_table_kref_release()

[Viresh Kumar]

There is a lot of stuff here which can be done outside of the big
opp_table_lock, do that. This helps avoiding few circular dependency
lockdeps around debugfs and interconnects.

Reported-by: Rob Clark <robdclark@gmail.com>
Reported-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
Rob: I know this only fixes the issue partially for you and I am still
looking into that. I just wanted to get this merged in early as this
fixes lockdep for other users as well.

 drivers/opp/core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 4ac4e7ce6b8b..0e0a5269dc82 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -1181,6 +1181,10 @@ static void _opp_table_kref_release(struct kref *kref)
 	struct opp_device *opp_dev, *temp;
 	int i;
 
+	/* Drop the lock as soon as we can */
+	list_del(&opp_table->node);
+	mutex_unlock(&opp_table_lock);
+
 	_of_clear_opp_table(opp_table);
 
 	/* Release clk */
@@ -1208,10 +1212,7 @@ static void _opp_table_kref_release(struct kref *kref)
 
 	mutex_destroy(&opp_table->genpd_virt_dev_lock);
 	mutex_destroy(&opp_table->lock);
-	list_del(&opp_table->node);
 	kfree(opp_table);
-
-	mutex_unlock(&opp_table_lock);
 }
 
 void dev_pm_opp_put_opp_table(struct opp_table *opp_table)
-- 
2.25.0.rc1.19.g042ed3e048af

Re: [PATCH] opp: Reduce the size of critical section in _opp_table_kref_release()

[Stephen Boyd]

Quoting Viresh Kumar (2020-10-27 00:57:06)
> There is a lot of stuff here which can be done outside of the big
> opp_table_lock, do that. This helps avoiding few circular dependency
> lockdeps around debugfs and interconnects.
> 
> Reported-by: Rob Clark <robdclark@gmail.com>
> Reported-by: Dmitry Osipenko <digetx@gmail.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---

Any Fixes tag?

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

Re: [PATCH] opp: Reduce the size of critical section in _opp_table_kref_release()

[Viresh Kumar]

On 28-10-20, 16:32, Stephen Boyd wrote:
> Quoting Viresh Kumar (2020-10-27 00:57:06)
> > There is a lot of stuff here which can be done outside of the big
> > opp_table_lock, do that. This helps avoiding few circular dependency
> > lockdeps around debugfs and interconnects.
> > 
> > Reported-by: Rob Clark <robdclark@gmail.com>
> > Reported-by: Dmitry Osipenko <digetx@gmail.com>
> > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> > ---
> 
> Any Fixes tag?

The circular dependency lockdep appears with 5.11 stuff and so we
don't need to fix it in any of the earlier releases. And so I didn't
wanted to bother with the fixes tag, as the code had been like this
for ever.

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

Thanks a lot. I was a bit worried about the crazy idea I had to solve
this :)

-- 
viresh

Re: [PATCH] opp: Reduce the size of critical section in _opp_table_kref_release()

[Dmitry Osipenko]

27.10.2020 10:57, Viresh Kumar пишет:
> There is a lot of stuff here which can be done outside of the big
> opp_table_lock, do that. This helps avoiding few circular dependency
> lockdeps around debugfs and interconnects.
> 
> Reported-by: Rob Clark <robdclark@gmail.com>
> Reported-by: Dmitry Osipenko <digetx@gmail.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> Rob: I know this only fixes the issue partially for you and I am still
> looking into that. I just wanted to get this merged in early as this
> fixes lockdep for other users as well.
> 
>  drivers/opp/core.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index 4ac4e7ce6b8b..0e0a5269dc82 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -1181,6 +1181,10 @@ static void _opp_table_kref_release(struct kref *kref)
>  	struct opp_device *opp_dev, *temp;
>  	int i;
>  
> +	/* Drop the lock as soon as we can */
> +	list_del(&opp_table->node);
> +	mutex_unlock(&opp_table_lock);
> +
>  	_of_clear_opp_table(opp_table);
>  
>  	/* Release clk */
> @@ -1208,10 +1212,7 @@ static void _opp_table_kref_release(struct kref *kref)
>  
>  	mutex_destroy(&opp_table->genpd_virt_dev_lock);
>  	mutex_destroy(&opp_table->lock);
> -	list_del(&opp_table->node);
>  	kfree(opp_table);
> -
> -	mutex_unlock(&opp_table_lock);
>  }
>  
>  void dev_pm_opp_put_opp_table(struct opp_table *opp_table)
> 

Fixes the NVIDIA Tegra devfreq driver lockup using WIP ICC patches, thanks.

Tested-by: Dmitry Osipenko <digetx@gmail.com>

Re: [PATCH] opp: Reduce the size of critical section in _opp_table_kref_release()

[Viresh Kumar]

On 29-10-20, 09:40, Viresh Kumar wrote:
> Thanks a lot. I was a bit worried about the crazy idea I had to solve
> this :)

Hmm, I thought this is the other patch where I had that crazy idea.
This one was quite straight forward :)

-- 
viresh

Re: [PATCH] opp: Reduce the size of critical section in _opp_table_kref_release()

[Stephen Boyd]

Quoting Viresh Kumar (2020-10-29 21:20:00)
> On 29-10-20, 09:40, Viresh Kumar wrote:
> > Thanks a lot. I was a bit worried about the crazy idea I had to solve
> > this :)
> 
> Hmm, I thought this is the other patch where I had that crazy idea.
> This one was quite straight forward :)
> 

What's the other crazy idea patch?

Re: [PATCH] opp: Reduce the size of critical section in _opp_table_kref_release()

[Viresh Kumar]

On 30-10-20, 19:53, Stephen Boyd wrote:
> Quoting Viresh Kumar (2020-10-29 21:20:00)
> > On 29-10-20, 09:40, Viresh Kumar wrote:
> > > Thanks a lot. I was a bit worried about the crazy idea I had to solve
> > > this :)
> > 
> > Hmm, I thought this is the other patch where I had that crazy idea.
> > This one was quite straight forward :)
> > 
> 
> What's the other crazy idea patch?

Surprisingly I never sent it properly, just shared in another email thread with
Rob Clark to test it out.

Sent that now.

-- 
viresh