[PATCH] cgroup: minor tweak for logic to get cgroup css

[PATCH] cgroup: minor tweak for logic to get cgroup css

[Peng Wang]

We could only handle the case that css exists
and css_try_get_online() fails.

Signed-off-by: Peng Wang <rocking@whu.edu.cn>
---
 kernel/cgroup/cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index bf9dbffd46b1..a988d77f6c6d 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -488,7 +488,7 @@ static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
 
 	rcu_read_lock();
 	css = cgroup_css(cgrp, ss);
-	if (!css || !css_tryget_online(css))
+	if (css && !css_tryget_online(css))
 		css = NULL;
 	rcu_read_unlock();
 
-- 
2.19.1

Re: [PATCH] cgroup: minor tweak for logic to get cgroup css

[Tejun Heo]

On Wed, Jul 03, 2019 at 10:07:49AM +0800, Peng Wang wrote:
> We could only handle the case that css exists
> and css_try_get_online() fails.

As css_tryget_online() can't handle NULL input, this is a bug fix.
Can you please clarify that in the description?

Thanks.

-- 
tejun

Re: [PATCH] cgroup: minor tweak for logic to get cgroup css

[Roman Gushchin]

On Mon, Jul 08, 2019 at 09:42:43AM -0700, Tejun Heo wrote:
> On Wed, Jul 03, 2019 at 10:07:49AM +0800, Peng Wang wrote:
> > We could only handle the case that css exists
> > and css_try_get_online() fails.
> 
> As css_tryget_online() can't handle NULL input, this is a bug fix.
> Can you please clarify that in the description?

-       if (!css || !css_tryget_online(css))
+       if (css && !css_tryget_online(css))

If css == NULL, !css is true, and the second part of the || statement
will not be evaluated. So it's not a bug fix.

Thanks!

Re: [PATCH] cgroup: minor tweak for logic to get cgroup css

[Tejun Heo]

On Mon, Jul 08, 2019 at 05:29:49PM +0000, Roman Gushchin wrote:
> On Mon, Jul 08, 2019 at 09:42:43AM -0700, Tejun Heo wrote:
> > On Wed, Jul 03, 2019 at 10:07:49AM +0800, Peng Wang wrote:
> > > We could only handle the case that css exists
> > > and css_try_get_online() fails.
> > 
> > As css_tryget_online() can't handle NULL input, this is a bug fix.
> > Can you please clarify that in the description?
> 
> -       if (!css || !css_tryget_online(css))
> +       if (css && !css_tryget_online(css))
> 
> If css == NULL, !css is true, and the second part of the || statement
> will not be evaluated. So it's not a bug fix.

Ah right, it's just confusing.  Will apply after the merge window.

Thanks.

-- 
tejun

Re: [PATCH] cgroup: minor tweak for logic to get cgroup css

[Tejun Heo]

On Wed, Jul 03, 2019 at 10:07:49AM +0800, Peng Wang wrote:
> We could only handle the case that css exists
> and css_try_get_online() fails.
> 
> Signed-off-by: Peng Wang <rocking@whu.edu.cn>

Applied to cgroup/for-5.4.

Thanks.

-- 
tejun