linux-kernel - [PATCH 3/3] msi: free msi_desc entry only after we've released the kobject

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Date:	Tue, 17 Sep 2013 03:47:44 +0200
From:	Veaceslav Falico <vfalico@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Veaceslav Falico <vfalico@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Subject: [PATCH 3/3] msi: free msi_desc entry only after we've released the kobject

Currently, we first do kobject_put(&entry->kobj) and the kfree(entry),
however kobject_put() doesn't guarantee us that it was the last reference
and that the kobj isn't used currently by someone else, so after we
kfree(entry) with the struct kobject - other users will begin using the
freed memory, instead of the actual kobject.

Fix this by using the kobject->release callback, which is called last when
the kobject is indeed not used and is cleaned up - it's msi_kobj_release(),
which can do the kfree(entry) safely (kobject_put/cleanup doesn't use the
kobj itself after ->release() was called, so we're safe).

In case we've failed to create the sysfs directories - just kfree()
it - cause we don't have the kobjects attached.

Also, remove the same functionality from populate_msi_sysfs(), cause on
failure we anyway call free_msi_irqs(), which will take care of all the
kobjects properly.

CC: Bjorn Helgaas <bhelgaas@...gle.com>
CC: linux-pci@...r.kernel.org
CC: linux-kernel@...r.kernel.org
Signed-off-by: Veaceslav Falico <vfalico@...hat.com>
---
 drivers/pci/msi.c | 27 +++++++++------------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 68da921..c9236e4 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -374,19 +374,22 @@ static void free_msi_irqs(struct pci_dev *dev)
 				iounmap(entry->mask_base);
 		}
 
+		list_del(&entry->list);
+
 		/*
 		 * Its possible that we get into this path
 		 * When populate_msi_sysfs fails, which means the entries
 		 * were not registered with sysfs.  In that case don't
-		 * unregister them.
+		 * unregister them, and just free. Otherwise the
+		 * kobject->release will take care of freeing the entry via
+		 * msi_kobj_release().
 		 */
 		if (entry->kobj.parent) {
 			kobject_del(&entry->kobj);
 			kobject_put(&entry->kobj);
+		} else {
+			kfree(entry);
 		}
-
-		list_del(&entry->list);
-		kfree(entry);
 	}
 
 	kset_unregister(dev->msi_kset);
@@ -512,6 +515,7 @@ static void msi_kobj_release(struct kobject *kobj)
 	struct msi_desc *entry = to_msi_desc(kobj);
 
 	pci_dev_put(entry->dev);
+	kfree(entry);
 }
 
 static struct kobj_type msi_irq_ktype = {
@@ -525,7 +529,6 @@ static int populate_msi_sysfs(struct pci_dev *pdev)
 	struct msi_desc *entry;
 	struct kobject *kobj;
 	int ret;
-	int count = 0;
 
 	pdev->msi_kset = kset_create_and_add("msi_irqs", NULL, &pdev->dev.kobj);
 	if (!pdev->msi_kset)
@@ -539,23 +542,11 @@ static int populate_msi_sysfs(struct pci_dev *pdev)
 				     "%u", entry->irq);
 		if (ret) {
 			pci_dev_put(pdev);
-			goto out_unroll;
+			return ret;
 		}
-
-		count++;
 	}
 
 	return 0;
-
-out_unroll:
-	list_for_each_entry(entry, &pdev->msi_list, list) {
-		if (!count)
-			break;
-		kobject_del(&entry->kobj);
-		kobject_put(&entry->kobj);
-		count--;
-	}
-	return ret;
 }
 
 /**
-- 
1.8.4

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