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Re: [PATCH 1/3] cgroup - removing superfluous rcu_read_lock_held check [message #41967 is a reply to message #41966]

Wed, 03 November 2010 08:58

Jiri Olsa
Messages: 6
Registered: November 2010

Junior Member

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@redhat.com>
>
> Reviewed-by: Li Zefan <lizf@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@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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[Message index]

		[PATCH 0/3] rcu - removing superfluous rcu_read_lock_held check By: Jiri Olsa on Mon, 01 November 2010 19:15
		[PATCH 1/3] cgroup - removing superfluous rcu_read_lock_held check By: Jiri Olsa on Mon, 01 November 2010 19:15
		Re: [PATCH 1/3] cgroup - removing superfluous rcu_read_lock_held check By: Li Zefan on Tue, 02 November 2010 17:54
		Re: [PATCH 1/3] cgroup - removing superfluous rcu_read_lock_held check By: Jiri Olsa on Wed, 03 November 2010 08:58
		Re: [PATCH 1/3] cgroup - removing superfluous rcu_read_lock_held check By: Li Zefan on Wed, 03 November 2010 18:40
		[PATCH 2/3] kernel, cred, kvm, security - removing superfluous rcu_read_lock_held check By: Jiri Olsa on Mon, 01 November 2010 19:15
		Re: [PATCH 2/3] kernel, cred, kvm, security - removing superfluous rcu_read_lock_held check By: Paolo Bonzini on Mon, 01 November 2010 22:42
		Re: [PATCH 2/3] kernel, cred, kvm, security - removing superfluous rcu_read_lock_held check By: Jiri Olsa on Tue, 02 November 2010 07:21
		[PATCH 3/3] net - removing superfluous rcu_read_lock_held check By: Jiri Olsa on Mon, 01 November 2010 19:15

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