linux-kernel - [RFC][PATCH 2/2] PNP: Avoid leaving unregistered device objects in lists

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Message-ID: <2977356.EqGQaLDDaS@vostro.rjw.lan>
Date:	Thu, 12 Mar 2015 02:22:50 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: [RFC][PATCH 2/2] PNP: Avoid leaving unregistered device objects in lists

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

pnp_register_protocol() and __pnp_add_device() both have the problem
that if device_register() fails, the objects they create will be left
in the lists they have been put on beforehand.  Unfortunately, that
is not handled by the callers of those routines either, so in case
of a device registration errors the PNP bus type's data structures
will end up in an inconsistent state.

Make pnp_register_protocol() and __pnp_add_device() remove the
objects from the lists if device registration fails.

In addition to that, since pnp_lock is a mutex now, device registration
can be put under it too to avoid the gap in which the device is in the
PNP bus type's lists, but has not been registered yet (or the other
way around during removal).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/pnp/core.c |   52 +++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 41 insertions(+), 11 deletions(-)

Index: linux-pm/drivers/pnp/core.c
===================================================================
--- linux-pm.orig/drivers/pnp/core.c
+++ linux-pm/drivers/pnp/core.c
@@ -42,6 +42,11 @@ void *pnp_alloc(long size)
 	return result;
 }
 
+static void pnp_remove_protocol(struct pnp_protocol *protocol)
+{
+	list_del(&protocol->protocol_list);
+}
+
 /**
  * pnp_protocol_register - adds a pnp protocol to the pnp layer
  * @protocol: pointer to the corresponding pnp_protocol structure
@@ -50,12 +55,13 @@ void *pnp_alloc(long size)
  */
 int pnp_register_protocol(struct pnp_protocol *protocol)
 {
-	int nodenum;
 	struct list_head *pos;
+	int nodenum, ret = 0;
 
 	INIT_LIST_HEAD(&protocol->devices);
 	INIT_LIST_HEAD(&protocol->cards);
 	nodenum = 0;
+
 	mutex_lock(&pnp_lock);
 
 	/* assign the lowest unused number */
@@ -67,12 +73,17 @@ int pnp_register_protocol(struct pnp_pro
 		}
 	}
 
-	list_add_tail(&protocol->protocol_list, &pnp_protocols);
-	mutex_unlock(&pnp_lock);
-
 	protocol->number = nodenum;
 	dev_set_name(&protocol->dev, "pnp%d", nodenum);
-	return device_register(&protocol->dev);
+
+	list_add_tail(&protocol->protocol_list, &pnp_protocols);
+
+	ret = device_register(&protocol->dev);
+	if (ret)
+		pnp_remove_protocol(protocol);
+
+	mutex_unlock(&pnp_lock);
+	return ret;
 }
 
 /**
@@ -82,9 +93,9 @@ int pnp_register_protocol(struct pnp_pro
 void pnp_unregister_protocol(struct pnp_protocol *protocol)
 {
 	mutex_lock(&pnp_lock);
-	list_del(&protocol->protocol_list);
-	mutex_unlock(&pnp_lock);
+	pnp_remove_protocol(protocol);
 	device_unregister(&protocol->dev);
+	mutex_unlock(&pnp_lock);
 }
 
 static void pnp_free_ids(struct pnp_dev *dev)
@@ -158,18 +169,38 @@ struct pnp_dev *pnp_alloc_dev(struct pnp
 	return dev;
 }
 
+static void pnp_delist_device(struct pnp_dev *dev)
+{
+	list_del(&dev->global_list);
+	list_del(&dev->protocol_list);
+}
+
 int __pnp_add_device(struct pnp_dev *dev)
 {
+	int ret;
+
 	pnp_fixup_device(dev);
 	dev->status = PNP_READY;
+
 	mutex_lock(&pnp_lock);
+
 	list_add_tail(&dev->global_list, &pnp_global);
 	list_add_tail(&dev->protocol_list, &dev->protocol->devices);
+
+	ret = device_register(&dev->dev);
+	if (ret) {
+		pnp_delist_device(dev);
+		mutex_unlock(&pnp_lock);
+		return ret;
+	}
+
 	mutex_unlock(&pnp_lock);
+
 	if (dev->protocol->can_wakeup)
 		device_set_wakeup_capable(&dev->dev,
 				dev->protocol->can_wakeup(dev));
-	return device_register(&dev->dev);
+
+	return 0;
 }
 
 /*
@@ -205,10 +236,9 @@ int pnp_add_device(struct pnp_dev *dev)
 void __pnp_remove_device(struct pnp_dev *dev)
 {
 	mutex_lock(&pnp_lock);
-	list_del(&dev->global_list);
-	list_del(&dev->protocol_list);
-	mutex_unlock(&pnp_lock);
+	pnp_delist_device(dev);
 	device_unregister(&dev->dev);
+	mutex_unlock(&pnp_lock);
 }
 
 static int __init pnp_init(void)

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