linux-kernel - [PATCH 3.2 083/152] virtio_pci: defer kfree until release callback

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Message-ID: <lsq.1424137613.966198054@decadent.org.uk>
Date:	Tue, 17 Feb 2015 01:46:53 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Michael S. Tsirkin" <mst@...hat.com>,
	"Sasha Levin" <sasha.levin@...cle.com>
Subject: [PATCH 3.2 083/152] virtio_pci: defer kfree until release callback

3.2.67-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sasha Levin <sasha.levin@...cle.com>

commit 63bd62a08ca45a0c804c3c89777edc7f76a2d6da upstream.

A struct device which has just been unregistered can live on past the
point at which a driver decides to drop it's initial reference to the
kobject gained on allocation.

This implies that when releasing a virtio device, we can't free a struct
virtio_device until the underlying struct device has been released,
which might not happen immediately on device_unregister().

Unfortunately, this is exactly what virtio pci does:
it has an empty release callback, and frees memory immediately
after unregistering the device.

This causes an easy to reproduce crash if CONFIG_DEBUG_KOBJECT_RELEASE
it enabled.

To fix, free the memory only once we know the device is gone in the release
callback.

Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/virtio/virtio_pci.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -612,11 +612,10 @@ static struct virtio_config_ops virtio_p
 
 static void virtio_pci_release_dev(struct device *_d)
 {
-	/*
-	 * No need for a release method as we allocate/free
-	 * all devices together with the pci devices.
-	 * Provide an empty one to avoid getting a warning from core.
-	 */
+	struct virtio_device *vdev = dev_to_virtio(_d);
+	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+
+	kfree(vp_dev);
 }
 
 /* the PCI probing function */
@@ -704,7 +703,6 @@ static void __devexit virtio_pci_remove(
 	pci_iounmap(pci_dev, vp_dev->ioaddr);
 	pci_release_regions(pci_dev);
 	pci_disable_device(pci_dev);
-	kfree(vp_dev);
 }
 
 #ifdef CONFIG_PM

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