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

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