linux-kernel - [PATCH 04/16] Drivers: hv: vmbus: avoid double kfree for device

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Message-Id: <1423016804-22014-4-git-send-email-kys@microsoft.com>
Date:	Tue,  3 Feb 2015 18:26:32 -0800
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	vkuznets@...hat.com
Cc:	Vitaly Kuznetsov 
	<"[mailto:vkuznets@...hat.com]"@linuxonhyperv.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 04/16] Drivers: hv: vmbus: avoid double kfree for device_obj

From: Vitaly Kuznetsov <[mailto:vkuznets@...hat.com]>

On driver shutdown device_obj is being freed twice:
1) In vmbus_free_channels()
2) vmbus_device_release() (which is being triggered by device_unregister() in
   vmbus_device_unregister().
This double kfree leads to the following sporadic crash on driver unload:

[   23.469876] general protection fault: 0000 [#1] SMP
[   23.470036] Modules linked in: hv_vmbus(-)
[   23.470036] CPU: 2 PID: 213 Comm: rmmod Not tainted 3.19.0-rc5_bug923184+ #488
[   23.470036] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090006  05/23/2012
[   23.470036] task: ffff880036ef1cb0 ti: ffff880036ce8000 task.ti: ffff880036ce8000
[   23.470036] RIP: 0010:[<ffffffff811d2e1b>]  [<ffffffff811d2e1b>] __kmalloc_node_track_caller+0xdb/0x1e0
[   23.470036] RSP: 0018:ffff880036cebcc8  EFLAGS: 00010246
...

When this crash does not happen on driver unload the similar one is expected if
we try to load hv_vmbus again.

Remove kfree from vmbus_free_channels() as freeing it from
vmbus_device_release() seems right.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 drivers/hv/channel_mgmt.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index ba4b25f..36bacc7 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -262,7 +262,6 @@ void vmbus_free_channels(void)
 
 	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
 		vmbus_device_unregister(channel->device_obj);
-		kfree(channel->device_obj);
 		free_channel(channel);
 	}
 }
-- 
1.7.4.1

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