From: Rebecca Schultz Zavin <rebecca@android.com>
Date: Mon, 20 Aug 2012 22:41:11 +0000 (-0700)
Subject: gpu: ion: Fix race between ion_import and ion_free
X-Git-Tag: firefly_0821_release~4090^2~682
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=3122d079e38b31d02e4814eee1b772a90ab88375;p=firefly-linux-kernel-4.4.55.git

gpu: ion: Fix race between ion_import and ion_free

If preemted during ion_free after the refcount is updated but
before the handle can be removed from the rb_tree, import
might find that handle in the tree and try to reuse it
when execution returns to free, the handle will be cleaned
up leaving the caller of import with a corrupt handle.
This patch modifies the locking to protect agains this race.

Change-Id: I31d18cc6398f0ca18e05cd919e2bcf86fa18d568
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
---

diff --git a/drivers/gpu/ion/ion.c b/drivers/gpu/ion/ion.c
index ddf8c007a75d..cde2d1c2dc59 100644
--- a/drivers/gpu/ion/ion.c
+++ b/drivers/gpu/ion/ion.c
@@ -253,8 +253,6 @@ static void ion_handle_destroy(struct kref *kref)
 	struct ion_client *client = handle->client;
 	struct ion_buffer *buffer = handle->buffer;
 
-	mutex_lock(&client->lock);
-
 	mutex_lock(&buffer->lock);
 	while (handle->kmap_cnt)
 		ion_handle_kmap_put(handle);
@@ -262,7 +260,6 @@ static void ion_handle_destroy(struct kref *kref)
 
 	if (!RB_EMPTY_NODE(&handle->node))
 		rb_erase(&handle->node, &client->handles);
-	mutex_unlock(&client->lock);
 
 	ion_buffer_put(buffer);
 	kfree(handle);
@@ -406,13 +403,13 @@ void ion_free(struct ion_client *client, struct ion_handle *handle)
 
 	mutex_lock(&client->lock);
 	valid_handle = ion_handle_validate(client, handle);
-	mutex_unlock(&client->lock);
 
 	if (!valid_handle) {
 		WARN(1, "%s: invalid handle passed to free.\n", __func__);
 		return;
 	}
 	ion_handle_put(handle);
+	mutex_unlock(&client->lock);
 }
 EXPORT_SYMBOL(ion_free);