2012-08-11 10:02:57

by Denis Efremov

Subject: [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 <[email protected]>
---
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

2012-08-12 01:16:46

by David Miller

Subject: Re: [PATCH] macvtap: rcu_dereference outside read-lock section

From: Denis Efremov <[email protected]>
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.

2012-08-12 06:23:21

by Denis Efremov

Subject: [PATCH v2] macvtap: rcu_dereference outside read-lock section

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 <[email protected]>
---
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

2012-08-12 08:48:39

by Michael S. Tsirkin

Subject: Re: [PATCH v2] macvtap: rcu_dereference outside read-lock section

On Sun, Aug 12, 2012 at 10:26:31AM +0400, Denis Efremov wrote:
> 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 <[email protected]>
> ---
> 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)

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 <[email protected]>


> return i;
> }
>
> --
> 1.7.7

2012-08-12 20:41:21

by David Miller

Subject: Re: [PATCH v2] macvtap: rcu_dereference outside read-lock section

From: "Michael S. Tsirkin" <[email protected]>
Date: Sun, 12 Aug 2012 11:49:29 +0300

> On Sun, Aug 12, 2012 at 10:26:31AM +0400, Denis Efremov wrote:
>> 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 <[email protected]>
...
> Acked-by: Michael S. Tsirkin <[email protected]>

Applied, thanks everyone.