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

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Date:   Tue, 10 Oct 2017 04:49:04 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Stephen Hemminger" <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "'Cathy Avery'" <cavery@...hat.com>,
        Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "'Rolf Neugebauer'" <rolf.neugebauer@...ker.com>,
        "apw@...onical.com" <apw@...onical.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>
Subject: [PATCH] vmbus: hvsock: add proper sync for
 vmbus_hvsock_device_unregister()


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: K. Y. Srinivasan <kys@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: Stephen Hemminger <sthemmin@...rosoft.com>
---

The patch is rebased on today's char-misc tree's char-misc-linus branch.
Please consider it for v4.14.

 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 018d2e0..379b0df 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);
-- 
2.7.4