linux-kernel - [PATCH v2 1/5] Drivers: hv: vmbus: avoid double kfree for device

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Message-Id: <1422377059-7858-2-git-send-email-vkuznets@redhat.com>
Date:	Tue, 27 Jan 2015 17:44:15 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>,
	devel@...uxdriverproject.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	linux-kernel@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>
Subject: [PATCH v2 1/5] Drivers: hv: vmbus: avoid double kfree for device_obj

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>
---
 drivers/hv/channel_mgmt.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 1d7df25..ac357b8 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -259,7 +259,6 @@ 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);
 	}
 }
-- 
1.9.3

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