linux-kernel - [PATCH V2 1/1] vmbus: hvsock: add proper sync for vmbus_hvsock_device

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Date:   Wed, 18 Oct 2017 02:08:40 -0700
From:   kys@...hange.microsoft.com
To:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
        vkuznets@...hat.com, jasowang@...hat.com,
        leann.ogasawara@...onical.com, marcelo.cerri@...onical.com,
        sthemmin@...rosoft.com
Cc:     Dexuan Cui <decui@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "K . Y . Srinivasan" <kys@...rosoft.com>
Subject: [PATCH V2 1/1] vmbus: hvsock: add proper sync for vmbus_hvsock_device_unregister()

From: Dexuan Cui <decui@...rosoft.com>

Without the patch, vmbus_hvsock_device_unregister() can destroy the device
prematurely when close() is called, and can cause NULl dereferencing or
potential data loss (the last portion of the data stream may be dropped
prematurely).

Signed-off-by: Dexuan Cui <decui@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: Stephen Hemminger <sthemmin@...rosoft.com>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
Please consider this for 4.14.
V2: Moved some comments around (Dan Carpenter)

 drivers/hv/channel_mgmt.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 018d2e0f8ec5..379b0df123be 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -937,7 +937,10 @@ void vmbus_hvsock_device_unregister(struct vmbus_channel *channel)
 {
 	BUG_ON(!is_hvsock_channel(channel));
 
-	channel->rescind = true;
+	/* We always get a rescind msg when a connection is closed. */
+	while (!READ_ONCE(channel->probe_done) || !READ_ONCE(channel->rescind))
+		msleep(1);
+
 	vmbus_device_unregister(channel->device_obj);
 }
 EXPORT_SYMBOL_GPL(vmbus_hvsock_device_unregister);
-- 
2.14.1