[PATCH] macvtap: rcu_dereference outside read-lock section

In this case it is not an error. rcu_dereference
occurs in update section. Replacement by
rcu_dereference_protected (with spinlock) in order to
prevent lockdep complaint.

Found by Linux Driver Verification project (linuxtesting.org)

Signed-off-by: Denis Efremov <redacted>
---
 drivers/net/macvtap.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 0737bd4..8ef11a8 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c

@@ -94,7 +94,8 @@ static int get_slot(struct macvlan_dev *vlan, struct macvtap_queue *q)
 	int i;
 
 	for (i = 0; i < MAX_MACVTAP_QUEUES; i++) {
-		if (rcu_dereference(vlan->taps[i]) == q)
+		if (rcu_dereference_protected(vlan->taps[i],
+				lockdep_is_held(&macvtap_lock)) == q)
 			return i;
 	}
 

-- 
1.7.7

From: Denis Efremov <redacted>
Date: Sat, 11 Aug 2012 14:05:27 +0400

-		if (rcu_dereference(vlan->taps[i]) == q)
+		if (rcu_dereference_protected(vlan->taps[i],
+				lockdep_is_held(&macvtap_lock)) == q)

You must use the proper combination of TAB character and spaces
to line up the lockdep_is_held() argument with the first column
after openning "(" on the previous line.

Never be lazy and use only TABs.

rcu_dereference occurs in update section. Replacement by
rcu_dereference_protected in order to prevent lockdep
complaint.

Found by Linux Driver Verification project (linuxtesting.org)

Signed-off-by: Denis Efremov <redacted>
---
 drivers/net/macvtap.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 0737bd4..0f0f9ce 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c

@@ -94,7 +94,8 @@ static int get_slot(struct macvlan_dev *vlan, struct macvtap_queue *q)
 	int i;
 
 	for (i = 0; i < MAX_MACVTAP_QUEUES; i++) {
-		if (rcu_dereference(vlan->taps[i]) == q)
+		if (rcu_dereference_protected(vlan->taps[i],
+					      lockdep_is_held(&macvtap_lock)) == q)
 			return i;
 	}
 

-- 
1.7.7

On Sun, Aug 12, 2012 at 10:26:31AM +0400, Denis Efremov wrote:

And now it's too long.  Maybe a temporary would be better?

		struct macvtap_queue *t;
		t = rcu_dereference_protected(vlan->taps[i],
					      lockdep_is_held(&macvtap_lock));
		if (t == q)
  			return i;
		
?

Anyway -

Acked-by: Michael S. Tsirkin <mst@redhat.com>

 			return i;
 	}
 
-- 
1.7.7

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Sun, 12 Aug 2012 11:49:29 +0300

On Sun, Aug 12, 2012 at 10:26:31AM +0400, Denis Efremov wrote:

quoted

rcu_dereference occurs in update section. Replacement by
rcu_dereference_protected in order to prevent lockdep
complaint.

Found by Linux Driver Verification project (linuxtesting.org)

Signed-off-by: Denis Efremov <redacted>

...

Acked-by: Michael S. Tsirkin <mst@redhat.com>

Applied, thanks everyone.