[Devel] Re: [PATCH 1/3] cgroup - removing superfluous rcu_read_lock_held check

[Jiri Olsa]

On Wed, Nov 03, 2010 at 01:54:55AM +0800, Li Zefan wrote:
> On 2010年11月02日 03:15, Jiri Olsa wrote:
> > hi,
> 
> This..
> 
> > the rcu_dereference_check is defined as
> > 
> > 	#define rcu_dereference_check(p, c) \
> > 	   __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
> > 
> > so the caller does not need to specify rcu_read_lock_held() condition.
> >
>  
> > wbr,
> > jirka
> 
> and this should be excluded from the changelog.
> 
> > 
> > 
> > Signed-off-by: Jiri Olsa <jolsa at redhat.com>
> 
> Reviewed-by: Li Zefan <lizf at cn.fujitsu.com>
> 
> However a nitpick:
> 
> > ---
> >  include/linux/cgroup.h |    1 -
> >  kernel/cgroup.c        |    6 ++----
> >  2 files changed, 2 insertions(+), 5 deletions(-)
> ...
> > @@ -4544,7 +4542,7 @@ unsigned short css_id(struct cgroup_subsys_state *css)
> >  	 * it's unchanged until freed.
> >  	 */
> >  	cssid = rcu_dereference_check(css->id,
> > -			rcu_read_lock_held() || atomic_read(&css->refcnt));
> > +			atomic_read(&css->refcnt));
> 
> Now the 2 lines can be made into one line and still fit into 80 chars.
> 
> >  
> >  	if (cssid)
> >  		return cssid->id;
> > @@ -4557,7 +4555,7 @@ unsigned short css_depth(struct cgroup_subsys_state *css)
> >  	struct css_id *cssid;
> >  
> >  	cssid = rcu_dereference_check(css->id,
> > -			rcu_read_lock_held() || atomic_read(&css->refcnt));
> > +			atomic_read(&css->refcnt));
> 
> dito
> 
> >  
> >  	if (cssid)
> >  		return cssid->depth;

attaching changed patch

wbr,
jirka

---
No need to specify rcu_read_lock_held() condition in rcu_dereference_check.


Signed-off-by: Jiri Olsa <jolsa at redhat.com>
---
 include/linux/cgroup.h |    1 -
 kernel/cgroup.c        |    8 ++------
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ed4ba11..caed568 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -536,7 +536,6 @@ static inline struct cgroup_subsys_state *cgroup_subsys_state(
  */
 #define task_subsys_state_check(task, subsys_id, __c)			\
 	rcu_dereference_check(task->cgroups->subsys[subsys_id],		\
-			      rcu_read_lock_held() ||			\
 			      lockdep_is_held(&task->alloc_lock) ||	\
 			      cgroup_lock_is_held() || (__c))
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 66a416b..a8d2221 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1687,7 +1687,6 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
 {
 	char *start;
 	struct dentry *dentry = rcu_dereference_check(cgrp->dentry,
-						      rcu_read_lock_held() ||
 						      cgroup_lock_is_held());
 
 	if (!dentry || cgrp == dummytop) {
@@ -1713,7 +1712,6 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
 			break;
 
 		dentry = rcu_dereference_check(cgrp->dentry,
-					       rcu_read_lock_held() ||
 					       cgroup_lock_is_held());
 		if (!cgrp->parent)
 			continue;
@@ -4543,8 +4541,7 @@ unsigned short css_id(struct cgroup_subsys_state *css)
 	 * on this or this is under rcu_read_lock(). Once css->id is allocated,
 	 * it's unchanged until freed.
 	 */
-	cssid = rcu_dereference_check(css->id,
-			rcu_read_lock_held() || atomic_read(&css->refcnt));
+	cssid = rcu_dereference_check(css->id, atomic_read(&css->refcnt));
 
 	if (cssid)
 		return cssid->id;
@@ -4556,8 +4553,7 @@ unsigned short css_depth(struct cgroup_subsys_state *css)
 {
 	struct css_id *cssid;
 
-	cssid = rcu_dereference_check(css->id,
-			rcu_read_lock_held() || atomic_read(&css->refcnt));
+	cssid = rcu_dereference_check(css->id, atomic_read(&css->refcnt));
 
 	if (cssid)
 		return cssid->depth;
-- 
1.7.1

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