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Date: Thu, 14 Nov 2019 13:58:32 -0800
From: Saravana Kannan <saravanak@...gle.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Cc: Android Kernel" <kernel-team@...roid.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] driver core: Allow device link operations inside sync_state()
On Thu, Nov 14, 2019 at 1:56 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Nov 14, 2019 at 8:42 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>
>
> 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
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