driver core: Fix adding device links to probing suppliers

Currently, it is not valid to add a device link from a consumer
driver ->probe callback to a supplier that is still probing too, but
generally this is a valid use case.  For example, if the consumer has
just acquired a resource that can only be available if the supplier
is functional, adding a device link to that supplier right away
should be safe (and even desirable arguably), but device_link_add()
doesn't handle that case correctly and the initial state of the link
created by it is wrong then.

To address this problem, change the initial state of device links
added between a probing supplier and a probing consumer to
DL_STATE_CONSUMER_PROBE and update device_links_driver_bound() to
skip such links on the supplier side.

With this change, if the supplier probe completes first,
device_links_driver_bound() called for it will skip the link state
update and when it is called for the consumer, the link state will
be updated to "active".  In turn, if the consumer probe completes
first, device_links_driver_bound() called for it will change the
state of the link to "active" and when it is called for the
supplier, the link status update will be skipped.

However, in principle the supplier or consumer probe may still fail
after the link has been added, so modify device_links_no_driver() to
change device links in the "active" or "consumer probe" state to
"dormant" on the supplier side and update __device_links_no_driver()
to change the link state to "available" only if it is "consumer
probe" or "active".

Then, if the supplier probe fails first, the leftover link to the
probing consumer will become "dormant" and device_links_no_driver()
called for the consumer (when its probe fails) will clean it up.
In turn, if the consumer probe fails first, it will either drop the
link, or change its state to "available" and, in the latter case,
when device_links_no_driver() is called for the supplier, it will
update the link state to "dormant".  [If the supplier probe fails,
but the consumer probe succeeds, which should not happen as long as
the consumer driver is correct, the link still will be around, but
it will be "dormant" until the supplier is probed again.]

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 66 insertions, 8 deletions

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 8611385e44b5..d58ea075f807 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -300,17 +300,26 @@ struct device_link *device_link_add(struct device *consumer,
 		link->status = DL_STATE_NONE;
 	} else {
 		switch (supplier->links.status) {
-		case DL_DEV_DRIVER_BOUND:
+		case DL_DEV_PROBING:
 			switch (consumer->links.status) {
 			case DL_DEV_PROBING:
 				/*
-				 * Some callers expect the link creation during
-				 * consumer driver probe to resume the supplier
-				 * even without DL_FLAG_RPM_ACTIVE.
+				 * A consumer driver can create a link to a
+				 * supplier that has not completed its probing
+				 * yet as long as it knows that the supplier is
+				 * already functional (for example, it has just
+				 * acquired some resources from the supplier).
 				 */
-				if (flags & DL_FLAG_PM_RUNTIME)
-					pm_runtime_resume(supplier);
-
+				link->status = DL_STATE_CONSUMER_PROBE;
+				break;
+			default:
+				link->status = DL_STATE_DORMANT;
+				break;
+			}
+			break;
+		case DL_DEV_DRIVER_BOUND:
+			switch (consumer->links.status) {
+			case DL_DEV_PROBING:
 				link->status = DL_STATE_CONSUMER_PROBE;
 				break;
 			case DL_DEV_DRIVER_BOUND:
@@ -331,6 +340,14 @@ struct device_link *device_link_add(struct device *consumer,
 	}
 
 	/*
+	 * Some callers expect the link creation during consumer driver probe to
+	 * resume the supplier even without DL_FLAG_RPM_ACTIVE.
+	 */
+	if (link->status == DL_STATE_CONSUMER_PROBE &&
+	    flags & DL_FLAG_PM_RUNTIME)
+		pm_runtime_resume(supplier);
+
+	/*
 	 * Move the consumer and all of the devices depending on it to the end
 	 * of dpm_list and the devices_kset list.
 	 *
@@ -518,6 +535,16 @@ void device_links_driver_bound(struct device *dev)
 		if (link->flags & DL_FLAG_STATELESS)
 			continue;
 
+		/*
+		 * Links created during consumer probe may be in the "consumer
+		 * probe" state to start with if the supplier is still probing
+		 * when they are created and they may become "active" if the
+		 * consumer probe returns first.  Skip them here.
+		 */
+		if (link->status == DL_STATE_CONSUMER_PROBE ||
+		    link->status == DL_STATE_ACTIVE)
+			continue;
+
 		WARN_ON(link->status != DL_STATE_DORMANT);
 		WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
 	}
@@ -557,17 +584,48 @@ static void __device_links_no_driver(struct device *dev)
 
 		if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER)
 			__device_link_del(&link->kref);
-		else if (link->status != DL_STATE_SUPPLIER_UNBIND)
+		else if (link->status == DL_STATE_CONSUMER_PROBE ||
+			 link->status == DL_STATE_ACTIVE)
 			WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
 	}
 
 	dev->links.status = DL_DEV_NO_DRIVER;
 }
 
+/**
+ * device_links_no_driver - Update links after failing driver probe.
+ * @dev: Device whose driver has just failed to probe.
+ *
+ * Clean up leftover links to consumers for @dev and invoke
+ * %__device_links_no_driver() to update links to suppliers for it as
+ * appropriate.
+ *
+ * Links with the DL_FLAG_STATELESS flag set are ignored.
+ */
 void device_links_no_driver(struct device *dev)
 {
+	struct device_link *link;
+
 	device_links_write_lock();
+
+	list_for_each_entry(link, &dev->links.consumers, s_node) {
+		if (link->flags & DL_FLAG_STATELESS)
+			continue;
+
+		/*
+		 * The probe has failed, so if the status of the link is
+		 * "consumer probe" or "active", it must have been added by
+		 * a probing consumer while this device was still probing.
+		 * Change its state to "dormant", as it represents a valid
+		 * relationship, but it is not functionally meaningful.
+		 */
+		if (link->status == DL_STATE_CONSUMER_PROBE ||
+		    link->status == DL_STATE_ACTIVE)
+			WRITE_ONCE(link->status, DL_STATE_DORMANT);
+	}
+
 	__device_links_no_driver(dev);
+
 	device_links_write_unlock();
 }