[tip/core/rcu,45/86] net,act_police,rcu: remove rcu_barrier()

Message ID 1304256126-26015-45-git-send-email-paulmck@linux.vnet.ibm.com
State New
Headers show

Commit Message

Paul E. McKenney May 1, 2011, 1:21 p.m.
From: Lai Jiangshan <laijs@cn.fujitsu.com>

There is no callback of this module maybe queued
since we use kfree_rcu(), we can safely remove the rcu_barrier().

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 net/sched/act_police.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

Comments

Josh Triplett May 1, 2011, 3:59 p.m. | #1
On Sun, May 01, 2011 at 06:21:25AM -0700, Paul E. McKenney wrote:
> From: Lai Jiangshan <laijs@cn.fujitsu.com>
> 
> There is no callback of this module maybe queued
> since we use kfree_rcu(), we can safely remove the rcu_barrier().
> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> Acked-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
>  net/sched/act_police.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/net/sched/act_police.c b/net/sched/act_police.c
> index d6bcd64..b3b9b32 100644
> --- a/net/sched/act_police.c
> +++ b/net/sched/act_police.c
> @@ -396,7 +396,6 @@ static void __exit
>  police_cleanup_module(void)
>  {
>  	tcf_unregister_action(&act_police_ops);
> -	rcu_barrier(); /* Wait for completion of call_rcu()'s (tcf_police_free_rcu) */
>  }

Very nice side-effect of having common callback code.  Seems worth doing
a review of other callers of rcu_barrier as well, to see if they still
need to do so.

- Josh Triplett
Paul E. McKenney May 2, 2011, 8:36 a.m. | #2
On Sun, May 01, 2011 at 08:59:35AM -0700, Josh Triplett wrote:
> On Sun, May 01, 2011 at 06:21:25AM -0700, Paul E. McKenney wrote:
> > From: Lai Jiangshan <laijs@cn.fujitsu.com>
> > 
> > There is no callback of this module maybe queued
> > since we use kfree_rcu(), we can safely remove the rcu_barrier().
> > 
> > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> > Acked-by: David S. Miller <davem@davemloft.net>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > ---
> >  net/sched/act_police.c |    1 -
> >  1 files changed, 0 insertions(+), 1 deletions(-)
> > 
> > diff --git a/net/sched/act_police.c b/net/sched/act_police.c
> > index d6bcd64..b3b9b32 100644
> > --- a/net/sched/act_police.c
> > +++ b/net/sched/act_police.c
> > @@ -396,7 +396,6 @@ static void __exit
> >  police_cleanup_module(void)
> >  {
> >  	tcf_unregister_action(&act_police_ops);
> > -	rcu_barrier(); /* Wait for completion of call_rcu()'s (tcf_police_free_rcu) */
> >  }
> 
> Very nice side-effect of having common callback code.  Seems worth doing
> a review of other callers of rcu_barrier as well, to see if they still
> need to do so.

Agreed, and good point on the review.  /me wonders how this review could
be automated...

							Thanx, Paul
Josh Triplett May 2, 2011, 5:50 p.m. | #3
On Mon, May 02, 2011 at 01:36:18AM -0700, Paul E. McKenney wrote:
> On Sun, May 01, 2011 at 08:59:35AM -0700, Josh Triplett wrote:
> > On Sun, May 01, 2011 at 06:21:25AM -0700, Paul E. McKenney wrote:
> > > From: Lai Jiangshan <laijs@cn.fujitsu.com>
> > > 
> > > There is no callback of this module maybe queued
> > > since we use kfree_rcu(), we can safely remove the rcu_barrier().
> > > 
> > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> > > Acked-by: David S. Miller <davem@davemloft.net>
> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > ---
> > >  net/sched/act_police.c |    1 -
> > >  1 files changed, 0 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/net/sched/act_police.c b/net/sched/act_police.c
> > > index d6bcd64..b3b9b32 100644
> > > --- a/net/sched/act_police.c
> > > +++ b/net/sched/act_police.c
> > > @@ -396,7 +396,6 @@ static void __exit
> > >  police_cleanup_module(void)
> > >  {
> > >  	tcf_unregister_action(&act_police_ops);
> > > -	rcu_barrier(); /* Wait for completion of call_rcu()'s (tcf_police_free_rcu) */
> > >  }
> > 
> > Very nice side-effect of having common callback code.  Seems worth doing
> > a review of other callers of rcu_barrier as well, to see if they still
> > need to do so.
> 
> Agreed, and good point on the review.  /me wonders how this review could
> be automated...

Build everything as a module, and for each module check whether it uses
the symbol rcu_barrier but not the symbol call_rcu.  Same for the
corresponding call_rcu_sched and call_rcu_bh.

Also, Coccinelle could likely handle simple cases of
call_rcu(function_that_calls_container_of_then_kfree), at least when
the call and the function appear in the same source file.

- Josh Triplett
Paul E. McKenney May 2, 2011, 10:21 p.m. | #4
On Mon, May 02, 2011 at 10:50:11AM -0700, Josh Triplett wrote:
> On Mon, May 02, 2011 at 01:36:18AM -0700, Paul E. McKenney wrote:
> > On Sun, May 01, 2011 at 08:59:35AM -0700, Josh Triplett wrote:
> > > On Sun, May 01, 2011 at 06:21:25AM -0700, Paul E. McKenney wrote:
> > > > From: Lai Jiangshan <laijs@cn.fujitsu.com>
> > > > 
> > > > There is no callback of this module maybe queued
> > > > since we use kfree_rcu(), we can safely remove the rcu_barrier().
> > > > 
> > > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> > > > Acked-by: David S. Miller <davem@davemloft.net>
> > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > ---
> > > >  net/sched/act_police.c |    1 -
> > > >  1 files changed, 0 insertions(+), 1 deletions(-)
> > > > 
> > > > diff --git a/net/sched/act_police.c b/net/sched/act_police.c
> > > > index d6bcd64..b3b9b32 100644
> > > > --- a/net/sched/act_police.c
> > > > +++ b/net/sched/act_police.c
> > > > @@ -396,7 +396,6 @@ static void __exit
> > > >  police_cleanup_module(void)
> > > >  {
> > > >  	tcf_unregister_action(&act_police_ops);
> > > > -	rcu_barrier(); /* Wait for completion of call_rcu()'s (tcf_police_free_rcu) */
> > > >  }
> > > 
> > > Very nice side-effect of having common callback code.  Seems worth doing
> > > a review of other callers of rcu_barrier as well, to see if they still
> > > need to do so.
> > 
> > Agreed, and good point on the review.  /me wonders how this review could
> > be automated...
> 
> Build everything as a module, and for each module check whether it uses
> the symbol rcu_barrier but not the symbol call_rcu.  Same for the
> corresponding call_rcu_sched and call_rcu_bh.

Good point -- I will give this a shot when I find AC power.

> Also, Coccinelle could likely handle simple cases of
> call_rcu(function_that_calls_container_of_then_kfree), at least when
> the call and the function appear in the same source file.

Good point -- it wasn't too hard by hand this time, but it would be
a good addition to RCU checking.

							Thanx, Paul

Patch

diff --git a/net/sched/act_police.c b/net/sched/act_police.c
index d6bcd64..b3b9b32 100644
--- a/net/sched/act_police.c
+++ b/net/sched/act_police.c
@@ -396,7 +396,6 @@  static void __exit
 police_cleanup_module(void)
 {
 	tcf_unregister_action(&act_police_ops);
-	rcu_barrier(); /* Wait for completion of call_rcu()'s (tcf_police_free_rcu) */
 }
 
 module_init(police_init_module);