[PATCH v3] driver core: Allow device link operations inside sync_state()

[PATCH v3] 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 | 80 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 72 insertions(+), 8 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index e6d3e6d485da..9a88bcfd5d33 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -695,7 +695,26 @@ 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
+ * @list: List head to queue the @dev 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 list_head *list)
 {
 	struct device_link *link;
 
@@ -709,12 +728,46 @@ 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 a list more
+	 * than once. This can happen if new consumers get added to the device
+	 * and probed before the list is flushed.
+	 */
 	dev->state_synced = true;
+
+	if (list_empty(&dev->links.defer_sync)) {
+		get_device(dev);
+		list_add_tail(&dev->links.defer_sync, list);
+	} else {
+		WARN_ON(1);
+	}
+}
+
+/**
+ * device_links_flush_sync_list - Call sync_state() on a list of devices
+ * @list: List of devices to call sync_state() on
+ *
+ * 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(struct list_head *list)
+{
+	struct device *dev, *tmp;
+
+	list_for_each_entry_safe(dev, tmp, 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);
+	}
 }
 
 void device_links_supplier_sync_state_pause(void)
@@ -727,6 +780,7 @@ void device_links_supplier_sync_state_pause(void)
 void device_links_supplier_sync_state_resume(void)
 {
 	struct device *dev, *tmp;
+	LIST_HEAD(sync_list);
 
 	device_links_write_lock();
 	if (!defer_sync_state_count) {
@@ -738,11 +792,17 @@ 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, &sync_list);
 	}
 out:
 	device_links_write_unlock();
+
+	device_links_flush_sync_list(&sync_list);
 }
 
 static int sync_state_resume_initcall(void)
@@ -772,6 +832,7 @@ static void __device_links_supplier_defer_sync(struct device *sup)
 void device_links_driver_bound(struct device *dev)
 {
 	struct device_link *link;
+	LIST_HEAD(sync_list);
 
 	/*
 	 * If a device probes successfully, it's expected to have created all
@@ -815,12 +876,15 @@ 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,
+							&sync_list);
 	}
 
 	dev->links.status = DL_DEV_DRIVER_BOUND;
 
 	device_links_write_unlock();
+
+	device_links_flush_sync_list(&sync_list);
 }
 
 static void device_link_drop_managed(struct device_link *link)
-- 
2.24.0.432.g9d3f5f5b63-goog

Re: [PATCH v3] driver core: Allow device link operations inside sync_state()

[Rafael J. Wysocki]

On Thu, Nov 14, 2019 at 11:23 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>
> ---
>  drivers/base/core.c | 80 ++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 72 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index e6d3e6d485da..9a88bcfd5d33 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -695,7 +695,26 @@ 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
> + * @list: List head to queue the @dev 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 list_head *list)
>  {
>         struct device_link *link;
>
> @@ -709,12 +728,46 @@ 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 a list more
> +        * than once. This can happen if new consumers get added to the device
> +        * and probed before the list is flushed.
> +        */
>         dev->state_synced = true;
> +
> +       if (list_empty(&dev->links.defer_sync)) {
> +               get_device(dev);
> +               list_add_tail(&dev->links.defer_sync, list);
> +       } else {
> +               WARN_ON(1);
> +       }

Now you can do:

        if (WARN_ON(!list_empty(&dev->links.defer_sync)))
                return;

        get_device(dev);
        list_add_tail(&dev->links.defer_sync, list);

The rest of the patch LGTM.

Re: [PATCH v3] driver core: Allow device link operations inside sync_state()

[Saravana Kannan]

On Thu, Nov 14, 2019 at 2:45 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Thu, Nov 14, 2019 at 11:23 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>
> > ---
> >  drivers/base/core.c | 80 ++++++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 72 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index e6d3e6d485da..9a88bcfd5d33 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -695,7 +695,26 @@ 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
> > + * @list: List head to queue the @dev 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 list_head *list)
> >  {
> >         struct device_link *link;
> >
> > @@ -709,12 +728,46 @@ 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 a list more
> > +        * than once. This can happen if new consumers get added to the device
> > +        * and probed before the list is flushed.
> > +        */
> >         dev->state_synced = true;
> > +
> > +       if (list_empty(&dev->links.defer_sync)) {
> > +               get_device(dev);
> > +               list_add_tail(&dev->links.defer_sync, list);
> > +       } else {
> > +               WARN_ON(1);
> > +       }
>
> Now you can do:
>
>         if (WARN_ON(!list_empty(&dev->links.defer_sync)))
>                 return;
>
>         get_device(dev);
>         list_add_tail(&dev->links.defer_sync, list);
>
> The rest of the patch LGTM.

Sending the patch right away in hopes of getting a reviewed-by or ack :)

-Saravana