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Message-ID: <CAJZ5v0izLzumE4xGZyxrVJ4OJ6SNytpA5fVZ4q7pC4ve0S7pYw@mail.gmail.com>
Date: Fri, 15 Nov 2019 00:53:16 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Saravana Kannan <saravanak@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
"Cc: Android Kernel" <kernel-team@...roid.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] driver core: Allow device link operations inside sync_state()
On Thu, Nov 14, 2019 at 11:56 PM Saravana Kannan <saravanak@...gle.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@...gle.com>
All of my comments have been addressed, so:
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> drivers/base/core.c | 79 ++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 71 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index e6d3e6d485da..42a672456432 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 +728,45 @@ 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 (WARN_ON(!list_empty(&dev->links.defer_sync)))
> + return;
> +
> + get_device(dev);
> + list_add_tail(&dev->links.defer_sync, list);
> +}
> +
> +/**
> + * 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 +779,7 @@ 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 +791,17 @@ 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 +831,7 @@ 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 +875,15 @@ 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
>
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