2012-08-18 12:09:11

by Denis Efremov

Subject: [PATCH] tcm_fc: rcu_deref outside rcu lock/unlock section

Use rcu_dereference_protected in order to prevent lockdep
complaint. Sequel of the patch 863555be

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Denis Efremov <[email protected]>
---
drivers/target/tcm_fc/tfc_sess.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/target/tcm_fc/tfc_sess.c b/drivers/target/tcm_fc/tfc_sess.c
index 87901fa..3c9e5b5 100644
--- a/drivers/target/tcm_fc/tfc_sess.c
+++ b/drivers/target/tcm_fc/tfc_sess.c
@@ -456,7 +456,9 @@ static void ft_prlo(struct fc_rport_priv *rdata)
struct ft_tport *tport;

mutex_lock(&ft_lport_lock);
- tport = rcu_dereference(rdata->local_port->prov[FC_TYPE_FCP]);
+ tport = rcu_dereference_protected(rdata->local_port->prov[FC_TYPE_FCP],
+ lockdep_is_held(&ft_lport_lock));
+
if (!tport) {
mutex_unlock(&ft_lport_lock);
return;
--
1.7.7

2012-08-18 22:35:37

by Nicholas A. Bellinger

Subject: Re: [PATCH] tcm_fc: rcu_deref outside rcu lock/unlock section

On Sat, 2012-08-18 at 16:10 +0400, Denis Efremov wrote:
> Use rcu_dereference_protected in order to prevent lockdep
> complaint. Sequel of the patch 863555be
>
> Found by Linux Driver Verification project (linuxtesting.org).
>
> Signed-off-by: Denis Efremov <[email protected]>
> ---
> drivers/target/tcm_fc/tfc_sess.c | 4 +++-
> 1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/target/tcm_fc/tfc_sess.c b/drivers/target/tcm_fc/tfc_sess.c
> index 87901fa..3c9e5b5 100644
> --- a/drivers/target/tcm_fc/tfc_sess.c
> +++ b/drivers/target/tcm_fc/tfc_sess.c
> @@ -456,7 +456,9 @@ static void ft_prlo(struct fc_rport_priv *rdata)
> struct ft_tport *tport;
>
> mutex_lock(&ft_lport_lock);
> - tport = rcu_dereference(rdata->local_port->prov[FC_TYPE_FCP]);
> + tport = rcu_dereference_protected(rdata->local_port->prov[FC_TYPE_FCP],
> + lockdep_is_held(&ft_lport_lock));
> +
> if (!tport) {
> mutex_unlock(&ft_lport_lock);
> return;

This looks OK to silence lockdep. CC'ing MDR + Kiran for good measure
here, and will move from target-pending queue -> master with their ACK.

Thanks Dennis!

--nab

2012-08-20 16:39:25

by Rustad, Mark D

Subject: Re: [PATCH] tcm_fc: rcu_deref outside rcu lock/unlock section

On Aug 18, 2012, at 3:35 PM, Nicholas A. Bellinger wrote:

> On Sat, 2012-08-18 at 16:10 +0400, Denis Efremov wrote:
>> Use rcu_dereference_protected in order to prevent lockdep
>> complaint. Sequel of the patch 863555be
>>
>> Found by Linux Driver Verification project (linuxtesting.org).
>>
>> Signed-off-by: Denis Efremov <[email protected]>
>> ---
>> drivers/target/tcm_fc/tfc_sess.c | 4 +++-
>> 1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/target/tcm_fc/tfc_sess.c b/drivers/target/tcm_fc/tfc_sess.c
>> index 87901fa..3c9e5b5 100644
>> --- a/drivers/target/tcm_fc/tfc_sess.c
>> +++ b/drivers/target/tcm_fc/tfc_sess.c
>> @@ -456,7 +456,9 @@ static void ft_prlo(struct fc_rport_priv *rdata)
>> struct ft_tport *tport;
>>
>> mutex_lock(&ft_lport_lock);
>> - tport = rcu_dereference(rdata->local_port->prov[FC_TYPE_FCP]);
>> + tport = rcu_dereference_protected(rdata->local_port->prov[FC_TYPE_FCP],
>> + lockdep_is_held(&ft_lport_lock));
>> +
>> if (!tport) {
>> mutex_unlock(&ft_lport_lock);
>> return;
>
> This looks OK to silence lockdep. CC'ing MDR + Kiran for good measure
> here, and will move from target-pending queue -> master with their ACK.
>
> Thanks Dennis!
>
> --nab


Ack. In fact I wonder why I didn't encounter it myself.

--
Mark Rustad, LAN Access Division, Intel Corporation