[PATCH v2] driver core: Allow device link operations inside sync_state()

[PATCH v2] driver core: Allow device link operations inside sync_state()

[Saravana Kannan]

Some sync_state() implementations might need to call APIs that in turn
make calls to device link APIs. So, do the sync_state() callbacks
without holding the device link lock.

Signed-off-by: Saravana Kannan <saravanak@google.com>
---
 drivers/base/core.c | 76 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 68 insertions(+), 8 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index e6d3e6d485da..2f14d4bf1472 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -48,6 +48,8 @@ early_param("sysfs.deprecated", sysfs_deprecated_setup);
 static LIST_HEAD(wait_for_suppliers);
 static DEFINE_MUTEX(wfs_lock);
 static LIST_HEAD(deferred_sync);
+static LIST_HEAD(sync_list);
+static DEFINE_MUTEX(sync_lock);
 static unsigned int defer_sync_state_count = 1;
 
 #ifdef CONFIG_SRCU
@@ -695,7 +697,23 @@ int device_links_check_suppliers(struct device *dev)
 	return ret;
 }
 
-static void __device_links_supplier_sync_state(struct device *dev)
+/** __device_links_queue_sync_state - Queue a device for sync_state() callback
+ * @dev: Device to call sync_state() on
+ *
+ * Queues a device for a sync_state() callback when the device links write lock
+ * isn't held. This allows the sync_state() execution flow to use device links
+ * APIs.  The caller must ensure this function is called with
+ * device_links_write_lock() held.
+ *
+ * This function does a get_device() to make sure the device is not freed while
+ * on this list.
+ *
+ * So the caller must also ensure that device_links_flush_sync_list() is called
+ * as soon as the caller releases device_links_write_lock().  This is necessary
+ * to make sure the sync_state() is called in a timely fashion and the
+ * put_device() is called on this device.
+ */
+static void __device_links_queue_sync_state(struct device *dev)
 {
 	struct device_link *link;
 
@@ -709,12 +727,48 @@ static void __device_links_supplier_sync_state(struct device *dev)
 			return;
 	}
 
-	if (dev->bus->sync_state)
-		dev->bus->sync_state(dev);
-	else if (dev->driver && dev->driver->sync_state)
-		dev->driver->sync_state(dev);
-
+	/*
+	 * Set the flag here to avoid adding the same device to the sync_list
+	 * more than once. This can happen if new consumers get added to the
+	 * device before the sync_list is flushed.
+	 */
 	dev->state_synced = true;
+
+	mutex_lock(&sync_lock);
+
+	if (list_empty(&dev->links.defer_sync)) {
+		get_device(dev);
+		list_add_tail(&dev->links.defer_sync, &sync_list);
+	} else {
+		WARN_ON(1);
+	}
+
+	mutex_unlock(&sync_lock);
+}
+
+/** device_links_flush_sync_list - Call sync_state() on devices queued for it
+ *
+ * Calls sync_state() on all the devices that have been queued for it. This
+ * function is used in conjunction with __device_links_queue_sync_state().
+ */
+static void device_links_flush_sync_list(void)
+{
+	struct device *dev, *tmp;
+
+	mutex_lock(&sync_lock);
+
+	list_for_each_entry_safe(dev, tmp, &sync_list, links.defer_sync) {
+		list_del_init(&dev->links.defer_sync);
+		device_lock(dev);
+		if (dev->bus->sync_state)
+			dev->bus->sync_state(dev);
+		else if (dev->driver && dev->driver->sync_state)
+			dev->driver->sync_state(dev);
+		device_unlock(dev);
+		put_device(dev);
+	}
+
+	mutex_unlock(&sync_lock);
 }
 
 void device_links_supplier_sync_state_pause(void)
@@ -738,11 +792,16 @@ void device_links_supplier_sync_state_resume(void)
 		goto out;
 
 	list_for_each_entry_safe(dev, tmp, &deferred_sync, links.defer_sync) {
-		__device_links_supplier_sync_state(dev);
+		/*
+		 * Delete from deferred_sync list before queuing it to
+		 * sync_list because defer_sync is used for both lists.
+		 */
 		list_del_init(&dev->links.defer_sync);
+		__device_links_queue_sync_state(dev);
 	}
 out:
 	device_links_write_unlock();
+	device_links_flush_sync_list();
 }
 
 static int sync_state_resume_initcall(void)
@@ -815,12 +874,13 @@ void device_links_driver_bound(struct device *dev)
 		if (defer_sync_state_count)
 			__device_links_supplier_defer_sync(link->supplier);
 		else
-			__device_links_supplier_sync_state(link->supplier);
+			__device_links_queue_sync_state(link->supplier);
 	}
 
 	dev->links.status = DL_DEV_DRIVER_BOUND;
 
 	device_links_write_unlock();
+	device_links_flush_sync_list();
 }
 
 static void device_link_drop_managed(struct device_link *link)
-- 
2.24.0.432.g9d3f5f5b63-goog

Re: [PATCH v2] driver core: Allow device link operations inside sync_state()

[Rafael J. Wysocki]

On Thu, Nov 14, 2019 at 8:42 PM Saravana Kannan <saravanak@google.com> wrote:
>
> Some sync_state() implementations might need to call APIs that in turn
> make calls to device link APIs. So, do the sync_state() callbacks
> without holding the device link lock.
>
> Signed-off-by: Saravana Kannan <saravanak@google.com>

It would have been kind of nice to let me respond to your last reply
before sending this.  Oh well.

> ---
>  drivers/base/core.c | 76 ++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 68 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index e6d3e6d485da..2f14d4bf1472 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -48,6 +48,8 @@ early_param("sysfs.deprecated", sysfs_deprecated_setup);
>  static LIST_HEAD(wait_for_suppliers);
>  static DEFINE_MUTEX(wfs_lock);
>  static LIST_HEAD(deferred_sync);
> +static LIST_HEAD(sync_list);
> +static DEFINE_MUTEX(sync_lock);

The two items above are not needed AFAICS.

>  static unsigned int defer_sync_state_count = 1;
>
>  #ifdef CONFIG_SRCU
> @@ -695,7 +697,23 @@ int device_links_check_suppliers(struct device *dev)
>         return ret;
>  }
>
> -static void __device_links_supplier_sync_state(struct device *dev)
> +/** __device_links_queue_sync_state - Queue a device for sync_state() callback

This should be

/**
 * __device_links_queue_sync_state - Queue a device for sync_state() callback

> + * @dev: Device to call sync_state() on
> + *
> + * Queues a device for a sync_state() callback when the device links write lock
> + * isn't held. This allows the sync_state() execution flow to use device links
> + * APIs.  The caller must ensure this function is called with
> + * device_links_write_lock() held.
> + *
> + * This function does a get_device() to make sure the device is not freed while
> + * on this list.
> + *
> + * So the caller must also ensure that device_links_flush_sync_list() is called
> + * as soon as the caller releases device_links_write_lock().  This is necessary
> + * to make sure the sync_state() is called in a timely fashion and the
> + * put_device() is called on this device.
> + */
> +static void __device_links_queue_sync_state(struct device *dev)

Pass a list head as a second arg.

>  {
>         struct device_link *link;
>
> @@ -709,12 +727,48 @@ static void __device_links_supplier_sync_state(struct device *dev)
>                         return;
>         }
>
> -       if (dev->bus->sync_state)
> -               dev->bus->sync_state(dev);
> -       else if (dev->driver && dev->driver->sync_state)
> -               dev->driver->sync_state(dev);
> -
> +       /*
> +        * Set the flag here to avoid adding the same device to the sync_list
> +        * more than once. This can happen if new consumers get added to the
> +        * device before the sync_list is flushed.
> +        */
>         dev->state_synced = true;
> +
> +       mutex_lock(&sync_lock);
> +
> +       if (list_empty(&dev->links.defer_sync)) {
> +               get_device(dev);
> +               list_add_tail(&dev->links.defer_sync, &sync_list);

Add it to the list that you have passed as the second arg.  No locking.

> +       } else {
> +               WARN_ON(1);
> +       }
> +
> +       mutex_unlock(&sync_lock);
> +}
> +
> +/** device_links_flush_sync_list - Call sync_state() on devices queued for it
> + *
> + * Calls sync_state() on all the devices that have been queued for it. This
> + * function is used in conjunction with __device_links_queue_sync_state().
> + */
> +static void device_links_flush_sync_list(void)

Make it take a list to flush as an arg.

> +{
> +       struct device *dev, *tmp;
> +
> +       mutex_lock(&sync_lock);

This isn't necessary.

> +
> +       list_for_each_entry_safe(dev, tmp, &sync_list, links.defer_sync) {
> +               list_del_init(&dev->links.defer_sync);
> +               device_lock(dev);

Empty lines around this?

> +               if (dev->bus->sync_state)
> +                       dev->bus->sync_state(dev);
> +               else if (dev->driver && dev->driver->sync_state)
> +                       dev->driver->sync_state(dev);
> +               device_unlock(dev);

And this?

> +               put_device(dev);
> +       }
> +
> +       mutex_unlock(&sync_lock);

This isn't necessary.

>  }
>
>  void device_links_supplier_sync_state_pause(void)
> @@ -738,11 +792,16 @@ void device_links_supplier_sync_state_resume(void)
>                 goto out;
>
>         list_for_each_entry_safe(dev, tmp, &deferred_sync, links.defer_sync) {
> -               __device_links_supplier_sync_state(dev);
> +               /*
> +                * Delete from deferred_sync list before queuing it to
> +                * sync_list because defer_sync is used for both lists.
> +                */
>                 list_del_init(&dev->links.defer_sync);
> +               __device_links_queue_sync_state(dev);

Use a local list (initially empty) in this function and pass it to the above.

>         }
>  out:
>         device_links_write_unlock();
> +       device_links_flush_sync_list();

Pass the local list here too.

>  }
>
>  static int sync_state_resume_initcall(void)
> @@ -815,12 +874,13 @@ void device_links_driver_bound(struct device *dev)
>                 if (defer_sync_state_count)
>                         __device_links_supplier_defer_sync(link->supplier);
>                 else
> -                       __device_links_supplier_sync_state(link->supplier);
> +                       __device_links_queue_sync_state(link->supplier);

Like in the previous case, use a local list (initially empty) in this
function and pass it to the above.

>         }
>
>         dev->links.status = DL_DEV_DRIVER_BOUND;
>
>         device_links_write_unlock();
> +       device_links_flush_sync_list();

And pass that list here too.

>  }
>
>  static void device_link_drop_managed(struct device_link *link)
> --

Re: [PATCH v2] driver core: Allow device link operations inside sync_state()

[Saravana Kannan]

On Thu, Nov 14, 2019 at 1:56 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Thu, Nov 14, 2019 at 8:42 PM Saravana Kannan <saravanak@google.com> wrote:
> >
> > Some sync_state() implementations might need to call APIs that in turn
> > make calls to device link APIs. So, do the sync_state() callbacks
> > without holding the device link lock.
> >
> > Signed-off-by: Saravana Kannan <saravanak@google.com>
>
> It would have been kind of nice to let me respond to your last reply
> before sending this.  Oh well.
>
> > ---
> >  drivers/base/core.c | 76 ++++++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 68 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index e6d3e6d485da..2f14d4bf1472 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -48,6 +48,8 @@ early_param("sysfs.deprecated", sysfs_deprecated_setup);
> >  static LIST_HEAD(wait_for_suppliers);
> >  static DEFINE_MUTEX(wfs_lock);
> >  static LIST_HEAD(deferred_sync);
> > +static LIST_HEAD(sync_list);
> > +static DEFINE_MUTEX(sync_lock);
>
> The two items above are not needed AFAICS.
>
> >  static unsigned int defer_sync_state_count = 1;
> >
> >  #ifdef CONFIG_SRCU
> > @@ -695,7 +697,23 @@ int device_links_check_suppliers(struct device *dev)
> >         return ret;
> >  }
> >
> > -static void __device_links_supplier_sync_state(struct device *dev)
> > +/** __device_links_queue_sync_state - Queue a device for sync_state() callback
>
> This should be
>
> /**
>  * __device_links_queue_sync_state - Queue a device for sync_state() callback
>
> > + * @dev: Device to call sync_state() on
> > + *
> > + * Queues a device for a sync_state() callback when the device links write lock
> > + * isn't held. This allows the sync_state() execution flow to use device links
> > + * APIs.  The caller must ensure this function is called with
> > + * device_links_write_lock() held.
> > + *
> > + * This function does a get_device() to make sure the device is not freed while
> > + * on this list.
> > + *
> > + * So the caller must also ensure that device_links_flush_sync_list() is called
> > + * as soon as the caller releases device_links_write_lock().  This is necessary
> > + * to make sure the sync_state() is called in a timely fashion and the
> > + * put_device() is called on this device.
> > + */
> > +static void __device_links_queue_sync_state(struct device *dev)
>
> Pass a list head as a second arg.
>
> >  {
> >         struct device_link *link;
> >
> > @@ -709,12 +727,48 @@ static void __device_links_supplier_sync_state(struct device *dev)
> >                         return;
> >         }
> >
> > -       if (dev->bus->sync_state)
> > -               dev->bus->sync_state(dev);
> > -       else if (dev->driver && dev->driver->sync_state)
> > -               dev->driver->sync_state(dev);
> > -
> > +       /*
> > +        * Set the flag here to avoid adding the same device to the sync_list
> > +        * more than once. This can happen if new consumers get added to the
> > +        * device before the sync_list is flushed.
> > +        */
> >         dev->state_synced = true;
> > +
> > +       mutex_lock(&sync_lock);
> > +
> > +       if (list_empty(&dev->links.defer_sync)) {
> > +               get_device(dev);
> > +               list_add_tail(&dev->links.defer_sync, &sync_list);
>
> Add it to the list that you have passed as the second arg.  No locking.
>
> > +       } else {
> > +               WARN_ON(1);
> > +       }
> > +
> > +       mutex_unlock(&sync_lock);
> > +}
> > +
> > +/** device_links_flush_sync_list - Call sync_state() on devices queued for it
> > + *
> > + * Calls sync_state() on all the devices that have been queued for it. This
> > + * function is used in conjunction with __device_links_queue_sync_state().
> > + */
> > +static void device_links_flush_sync_list(void)
>
> Make it take a list to flush as an arg.
>
> > +{
> > +       struct device *dev, *tmp;
> > +
> > +       mutex_lock(&sync_lock);
>
> This isn't necessary.
>
> > +
> > +       list_for_each_entry_safe(dev, tmp, &sync_list, links.defer_sync) {
> > +               list_del_init(&dev->links.defer_sync);
> > +               device_lock(dev);
>
> Empty lines around this?
>
> > +               if (dev->bus->sync_state)
> > +                       dev->bus->sync_state(dev);
> > +               else if (dev->driver && dev->driver->sync_state)
> > +                       dev->driver->sync_state(dev);
> > +               device_unlock(dev);
>
> And this?
>
> > +               put_device(dev);
> > +       }
> > +
> > +       mutex_unlock(&sync_lock);
>
> This isn't necessary.
>
> >  }
> >
> >  void device_links_supplier_sync_state_pause(void)
> > @@ -738,11 +792,16 @@ void device_links_supplier_sync_state_resume(void)
> >                 goto out;
> >
> >         list_for_each_entry_safe(dev, tmp, &deferred_sync, links.defer_sync) {
> > -               __device_links_supplier_sync_state(dev);
> > +               /*
> > +                * Delete from deferred_sync list before queuing it to
> > +                * sync_list because defer_sync is used for both lists.
> > +                */
> >                 list_del_init(&dev->links.defer_sync);
> > +               __device_links_queue_sync_state(dev);
>
> Use a local list (initially empty) in this function and pass it to the above.
>
> >         }
> >  out:
> >         device_links_write_unlock();
> > +       device_links_flush_sync_list();
>
> Pass the local list here too.
>
> >  }
> >
> >  static int sync_state_resume_initcall(void)
> > @@ -815,12 +874,13 @@ void device_links_driver_bound(struct device *dev)
> >                 if (defer_sync_state_count)
> >                         __device_links_supplier_defer_sync(link->supplier);
> >                 else
> > -                       __device_links_supplier_sync_state(link->supplier);
> > +                       __device_links_queue_sync_state(link->supplier);
>
> Like in the previous case, use a local list (initially empty) in this
> function and pass it to the above.
>
> >         }
> >
> >         dev->links.status = DL_DEV_DRIVER_BOUND;
> >
> >         device_links_write_unlock();
> > +       device_links_flush_sync_list();
>
> And pass that list here too.
>
> >  }
> >
> >  static void device_link_drop_managed(struct device_link *link)
> > --

Ok, I'll move it to a local list, add the blank lines and send out a patch?

-Saravana

Re: [PATCH v2] driver core: Allow device link operations inside sync_state()

[Rafael J. Wysocki]

On Thu, Nov 14, 2019 at 10:59 PM Saravana Kannan <saravanak@google.com> wrote:
>
> On Thu, Nov 14, 2019 at 1:56 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Thu, Nov 14, 2019 at 8:42 PM Saravana Kannan <saravanak@google.com> wrote:
> > >
> > > Some sync_state() implementations might need to call APIs that in turn
> > > make calls to device link APIs. So, do the sync_state() callbacks
> > > without holding the device link lock.
> > >
> > > Signed-off-by: Saravana Kannan <saravanak@google.com>
> >
> > It would have been kind of nice to let me respond to your last reply
> > before sending this.  Oh well.
> >
> > > ---
> > >  drivers/base/core.c | 76 ++++++++++++++++++++++++++++++++++++++++-----
> > >  1 file changed, 68 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > > index e6d3e6d485da..2f14d4bf1472 100644
> > > --- a/drivers/base/core.c
> > > +++ b/drivers/base/core.c
> > > @@ -48,6 +48,8 @@ early_param("sysfs.deprecated", sysfs_deprecated_setup);
> > >  static LIST_HEAD(wait_for_suppliers);
> > >  static DEFINE_MUTEX(wfs_lock);
> > >  static LIST_HEAD(deferred_sync);
> > > +static LIST_HEAD(sync_list);
> > > +static DEFINE_MUTEX(sync_lock);
> >
> > The two items above are not needed AFAICS.
> >
> > >  static unsigned int defer_sync_state_count = 1;
> > >
> > >  #ifdef CONFIG_SRCU
> > > @@ -695,7 +697,23 @@ int device_links_check_suppliers(struct device *dev)
> > >         return ret;
> > >  }
> > >
> > > -static void __device_links_supplier_sync_state(struct device *dev)
> > > +/** __device_links_queue_sync_state - Queue a device for sync_state() callback
> >
> > This should be
> >
> > /**
> >  * __device_links_queue_sync_state - Queue a device for sync_state() callback
> >
> > > + * @dev: Device to call sync_state() on
> > > + *
> > > + * Queues a device for a sync_state() callback when the device links write lock
> > > + * isn't held. This allows the sync_state() execution flow to use device links
> > > + * APIs.  The caller must ensure this function is called with
> > > + * device_links_write_lock() held.
> > > + *
> > > + * This function does a get_device() to make sure the device is not freed while
> > > + * on this list.
> > > + *
> > > + * So the caller must also ensure that device_links_flush_sync_list() is called
> > > + * as soon as the caller releases device_links_write_lock().  This is necessary
> > > + * to make sure the sync_state() is called in a timely fashion and the
> > > + * put_device() is called on this device.
> > > + */
> > > +static void __device_links_queue_sync_state(struct device *dev)
> >
> > Pass a list head as a second arg.
> >
> > >  {
> > >         struct device_link *link;
> > >
> > > @@ -709,12 +727,48 @@ static void __device_links_supplier_sync_state(struct device *dev)
> > >                         return;
> > >         }
> > >
> > > -       if (dev->bus->sync_state)
> > > -               dev->bus->sync_state(dev);
> > > -       else if (dev->driver && dev->driver->sync_state)
> > > -               dev->driver->sync_state(dev);
> > > -
> > > +       /*
> > > +        * Set the flag here to avoid adding the same device to the sync_list
> > > +        * more than once. This can happen if new consumers get added to the
> > > +        * device before the sync_list is flushed.
> > > +        */
> > >         dev->state_synced = true;
> > > +
> > > +       mutex_lock(&sync_lock);
> > > +
> > > +       if (list_empty(&dev->links.defer_sync)) {
> > > +               get_device(dev);
> > > +               list_add_tail(&dev->links.defer_sync, &sync_list);
> >
> > Add it to the list that you have passed as the second arg.  No locking.
> >
> > > +       } else {
> > > +               WARN_ON(1);
> > > +       }
> > > +
> > > +       mutex_unlock(&sync_lock);
> > > +}
> > > +
> > > +/** device_links_flush_sync_list - Call sync_state() on devices queued for it
> > > + *
> > > + * Calls sync_state() on all the devices that have been queued for it. This
> > > + * function is used in conjunction with __device_links_queue_sync_state().
> > > + */
> > > +static void device_links_flush_sync_list(void)
> >
> > Make it take a list to flush as an arg.
> >
> > > +{
> > > +       struct device *dev, *tmp;
> > > +
> > > +       mutex_lock(&sync_lock);
> >
> > This isn't necessary.
> >
> > > +
> > > +       list_for_each_entry_safe(dev, tmp, &sync_list, links.defer_sync) {
> > > +               list_del_init(&dev->links.defer_sync);
> > > +               device_lock(dev);
> >
> > Empty lines around this?
> >
> > > +               if (dev->bus->sync_state)
> > > +                       dev->bus->sync_state(dev);
> > > +               else if (dev->driver && dev->driver->sync_state)
> > > +                       dev->driver->sync_state(dev);
> > > +               device_unlock(dev);
> >
> > And this?
> >
> > > +               put_device(dev);
> > > +       }
> > > +
> > > +       mutex_unlock(&sync_lock);
> >
> > This isn't necessary.
> >
> > >  }
> > >
> > >  void device_links_supplier_sync_state_pause(void)
> > > @@ -738,11 +792,16 @@ void device_links_supplier_sync_state_resume(void)
> > >                 goto out;
> > >
> > >         list_for_each_entry_safe(dev, tmp, &deferred_sync, links.defer_sync) {
> > > -               __device_links_supplier_sync_state(dev);
> > > +               /*
> > > +                * Delete from deferred_sync list before queuing it to
> > > +                * sync_list because defer_sync is used for both lists.
> > > +                */
> > >                 list_del_init(&dev->links.defer_sync);
> > > +               __device_links_queue_sync_state(dev);
> >
> > Use a local list (initially empty) in this function and pass it to the above.
> >
> > >         }
> > >  out:
> > >         device_links_write_unlock();
> > > +       device_links_flush_sync_list();
> >
> > Pass the local list here too.
> >
> > >  }
> > >
> > >  static int sync_state_resume_initcall(void)
> > > @@ -815,12 +874,13 @@ void device_links_driver_bound(struct device *dev)
> > >                 if (defer_sync_state_count)
> > >                         __device_links_supplier_defer_sync(link->supplier);
> > >                 else
> > > -                       __device_links_supplier_sync_state(link->supplier);
> > > +                       __device_links_queue_sync_state(link->supplier);
> >
> > Like in the previous case, use a local list (initially empty) in this
> > function and pass it to the above.
> >
> > >         }
> > >
> > >         dev->links.status = DL_DEV_DRIVER_BOUND;
> > >
> > >         device_links_write_unlock();
> > > +       device_links_flush_sync_list();
> >
> > And pass that list here too.
> >
> > >  }
> > >
> > >  static void device_link_drop_managed(struct device_link *link)
> > > --
>
> Ok, I'll move it to a local list, add the blank lines and send out a patch?

Works for me. :-)