linux-kernel - [PATCH 3.16.y-ckt 58/58] virtio_pci: document why we defer kfree

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Message-Id: <1424353948-31863-59-git-send-email-luis.henriques@canonical.com>
Date:	Thu, 19 Feb 2015 13:52:28 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 58/58] virtio_pci: document why we defer kfree

3.16.7-ckt7 -stable review patch.  If anyone has any objections, please let me know.

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

From: "Michael S. Tsirkin" <mst@...hat.com>

commit a1eb03f546d651a8f39c7d0692b1f7f5b4e7e3cd upstream.

The reason we defer kfree until release function is because it's a
general rule for kobjects: kfree of the reference counter itself is only
legal in the release function.

Previous patch didn't make this clear, document this in code.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
[ luis: backported to 3.16:
  - file rename: virtio_pci_legacy.c -> virtio_pci.c ]
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/virtio/virtio_pci.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index a46570005a98..52c4607fec9e 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -671,6 +671,9 @@ static void virtio_pci_release_dev(struct device *_d)
 	struct virtio_device *vdev = dev_to_virtio(_d);
 	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
 
+	/* As struct device is a kobject, it's not safe to
+	 * free the memory (including the reference counter itself)
+	 * until it's release callback. */
 	kfree(vp_dev);
 }
 
-- 
2.1.4

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