linux-kernel - [PATCH 3/4] Drivers: hv: vmbus: protect vmbus_get_outgoing

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Message-Id: <1422982839-3948-4-git-send-email-vkuznets@redhat.com>
Date:	Tue,  3 Feb 2015 18:00:38 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>,
	devel@...uxdriverproject.org
Cc:	Haiyang Zhang <haiyangz@...rosoft.com>,
	linux-kernel@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>,
	Jason Wang <jasowang@...hat.com>
Subject: [PATCH 3/4] Drivers: hv: vmbus: protect vmbus_get_outgoing_channel() against channel removal

list_for_each_safe() we have in vmbus_get_outgoing_channel() works, however, we
are not protected against the channel being removed (e.g. after receiving rescind
offer). Users of this function (storvsc_do_io() is the only one at this moment)
can get a link to an already freed channel. Make vmbus_get_outgoing_channel()
search holding primary->lock as child channels are not being freed unless they're
removed from parent's list.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 drivers/hv/channel_mgmt.c  | 10 +++++++---
 drivers/scsi/storvsc_drv.c |  2 ++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index fdccd16..af6243c 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -881,18 +881,20 @@ cleanup:
  */
 struct vmbus_channel *vmbus_get_outgoing_channel(struct vmbus_channel *primary)
 {
-	struct list_head *cur, *tmp;
+	struct list_head *cur;
 	int cur_cpu;
 	struct vmbus_channel *cur_channel;
 	struct vmbus_channel *outgoing_channel = primary;
 	int cpu_distance, new_cpu_distance;
+	unsigned long flags;
 
 	if (list_empty(&primary->sc_list))
-		return outgoing_channel;
+		return vmbus_get_channel(outgoing_channel);
 
 	cur_cpu = hv_context.vp_index[get_cpu()];
 	put_cpu();
-	list_for_each_safe(cur, tmp, &primary->sc_list) {
+	spin_lock_irqsave(&primary->lock, flags);
+	list_for_each(cur, &primary->sc_list) {
 		cur_channel = list_entry(cur, struct vmbus_channel, sc_list);
 		if (cur_channel->state != CHANNEL_OPENED_STATE)
 			continue;
@@ -913,6 +915,8 @@ struct vmbus_channel *vmbus_get_outgoing_channel(struct vmbus_channel *primary)
 
 		outgoing_channel = cur_channel;
 	}
+	outgoing_channel = vmbus_get_channel(outgoing_channel);
+	spin_unlock_irqrestore(&primary->lock, flags);
 
 	return outgoing_channel;
 }
diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 4cff0dd..3b9b851 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1370,6 +1370,8 @@ static int storvsc_do_io(struct hv_device *device,
 			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
 	}
 
+	vmbus_put_channel(outgoing_channel);
+
 	if (ret != 0)
 		return ret;
 
-- 
1.9.3

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