driver core: Fix sleeping in invalid context during device link deletion

Marek and Guenter reported that commit 287905e6 ("driver core:
Expose device link details in sysfs") caused sleeping/scheduling while
atomic warnings.

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:935
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 12, name: kworker/0:1
2 locks held by kworker/0:1/12:
  #0: ee8074a8 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work+0x174/0x7dc
  #1: ee921f20 ((work_completion)(&sdp->work)){+.+.}-{0:0}, at: process_one_work+0x174/0x7dc
Preemption disabled at:
[<c01b10f0>] srcu_invoke_callbacks+0xc0/0x154
----- 8< ----- SNIP
[<c064590c>] (device_del) from [<c0645c9c>] (device_unregister+0x24/0x64)
[<c0645c9c>] (device_unregister) from [<c01b10fc>] (srcu_invoke_callbacks+0xcc/0x154)
[<c01b10fc>] (srcu_invoke_callbacks) from [<c01493c4>] (process_one_work+0x234/0x7dc)
[<c01493c4>] (process_one_work) from [<c01499b0>] (worker_thread+0x44/0x51c)
[<c01499b0>] (worker_thread) from [<c0150bf4>] (kthread+0x158/0x1a0)
[<c0150bf4>] (kthread) from [<c0100114>] (ret_from_fork+0x14/0x20)
Exception stack(0xee921fb0 to 0xee921ff8)

This was caused by the device link device being released in the context
of srcu_invoke_callbacks().  There is no need to wait till the RCU
callback to release the device link device.  So release the device
earlier and move the call_srcu() into the device release code. That way,
the memory will get freed only after the device is released AND the RCU
callback is called.

Fixes: 287905e6 ("driver core: Expose device link details in sysfs")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200716214523.2924704-1-saravanak@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/core.c

@@ -307,10 +307,34 @@ static struct attribute *devlink_attrs[] = {
 };
 ATTRIBUTE_GROUPS(devlink);
 
+static void device_link_free(struct device_link *link)
+{
+	while (refcount_dec_not_one(&link->rpm_active))
+		pm_runtime_put(link->supplier);
+
+	put_device(link->consumer);
+	put_device(link->supplier);
+	kfree(link);
+}
+
+#ifdef CONFIG_SRCU
+static void __device_link_free_srcu(struct rcu_head *rhead)
+{
+	device_link_free(container_of(rhead, struct device_link, rcu_head));
+}
+
 static void devlink_dev_release(struct device *dev)
 {
-	kfree(to_devlink(dev));
+	struct device_link *link = to_devlink(dev);
+
+	call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
 }
+#else
+static void devlink_dev_release(struct device *dev)
+{
+	device_link_free(to_devlink(dev));
+}
+#endif
 
 static struct class devlink_class = {
 	.name = "devlink",
@@ -731,22 +755,7 @@ static void device_link_add_missing_supplier_links(void)
 	mutex_unlock(&wfs_lock);
 }
 
-static void device_link_free(struct device_link *link)
-{
-	while (refcount_dec_not_one(&link->rpm_active))
-		pm_runtime_put(link->supplier);
-
-	put_device(link->consumer);
-	put_device(link->supplier);
-	device_unregister(&link->link_dev);
-}
-
 #ifdef CONFIG_SRCU
-static void __device_link_free_srcu(struct rcu_head *rhead)
-{
-	device_link_free(container_of(rhead, struct device_link, rcu_head));
-}
-
 static void __device_link_del(struct kref *kref)
 {
 	struct device_link *link = container_of(kref, struct device_link, kref);
@@ -759,7 +768,7 @@ static void __device_link_del(struct kref *kref)
 
 	list_del_rcu(&link->s_node);
 	list_del_rcu(&link->c_node);
-	call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
+	device_unregister(&link->link_dev);
 }
 #else /* !CONFIG_SRCU */
 static void __device_link_del(struct kref *kref)
@@ -774,7 +783,7 @@ static void __device_link_del(struct kref *kref)
 
 	list_del(&link->s_node);
 	list_del(&link->c_node);
-	device_link_free(link);
+	device_unregister(&link->link_dev);
 }
 #endif /* !CONFIG_SRCU */