linux-kernel - [PATCH] vmbus: don't acquire the mutex in vmbus_hvsock_device

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Date:   Wed, 16 Aug 2017 03:40:40 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "apw@...onical.com" <apw@...onical.com>,
        Andy Lutomirski <luto@...nel.org>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        "leann.ogasawara@...onical.com" <leann.ogasawara@...onical.com>,
        "Rolf Neugebauer" <rolf.neugebauer@...ker.com>,
        'Marcelo Cerri' <marcelo.cerri@...onical.com>
Subject: [PATCH] vmbus: don't acquire the mutex in
 vmbus_hvsock_device_unregister()


Due to commit 54a66265d675 ("Drivers: hv: vmbus: Fix rescind handling"),
we need this patch to resolve the below deadlock:

after we get the mutex in vmbus_hvsock_device_unregister() and call
vmbus_device_unregister() -> device_unregister() -> ... -> device_release()
-> vmbus_device_release(), we'll get a deadlock, because
vmbus_device_release() tries to get the same mutex.

Signed-off-by: Dexuan Cui <decui@...rosoft.com>
Cc: K. Y. Srinivasan <kys@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: Stephen Hemminger <sthemmin@...rosoft.com>
---
 drivers/hv/channel_mgmt.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 4bbb8de..0373611 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -922,14 +922,10 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
 
 void vmbus_hvsock_device_unregister(struct vmbus_channel *channel)
 {
-	mutex_lock(&vmbus_connection.channel_mutex);
-
 	BUG_ON(!is_hvsock_channel(channel));
 
 	channel->rescind = true;
 	vmbus_device_unregister(channel->device_obj);
-
-	mutex_unlock(&vmbus_connection.channel_mutex);
 }
 EXPORT_SYMBOL_GPL(vmbus_hvsock_device_unregister);
 
-- 
2.7.4