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Re: [PATCH 3/2] cgroup_show_path: use a new helper to get current cgns css_set

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  Re: [PATCH 3/2] cgroup_show_path: use a new helper to get current  cgns css_set "Serge E. Hallyn" <serge@hallyn.com> - 2016-04-29 23:50 +0200
    Re: [PATCH 3/2] cgroup_show_path: use a new helper to get current  cgns css_set Tejun Heo <tj@kernel.org> - 2016-05-02 18:40 +0200
      Re: [PATCH 3/2] cgroup_show_path: use a new helper to get current  cgns css_set "Serge E. Hallyn" <serge@hallyn.com> - 2016-05-03 16:30 +0200

#1391454 — Re: [PATCH 3/2] cgroup_show_path: use a new helper to get current cgns css_set

[ I'm sorry, apparently I had sent the wrong version of this patch.  Here
is the correct one from
https://git.kernel.org/cgit/linux/kernel/git/sergeh/linux-security.git/commit/?h=2016-04-17/kernfs.show&id=79f784037098fddae92258579ef494537a12f1b2
Thanks Michael for pointing that out
]

Since we're getting current's cgroup namespace info, and are
not modifying it, we don't need the cgroup_mutex.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
---
 kernel/cgroup.c | 40 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9a0d7b3..1243e3e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1215,6 +1215,41 @@ static void cgroup_destroy_root(struct cgroup_root *root)
 	cgroup_free_root(root);
 }
 
+/*
+ * look up cgroup associated with current task's cgroup namespace on the
+ * specified hierarchy
+ */
+static struct cgroup *
+current_cgns_cgroup_from_root(struct cgroup_root *root)
+{
+	struct cgroup *res = NULL;
+	struct css_set *cset;
+
+	lockdep_assert_held(&css_set_lock);
+
+	rcu_read_lock();
+
+	cset = current->nsproxy->cgroup_ns->root_cset;
+	if (cset == &init_css_set) {
+		res = &root->cgrp;
+	} else {
+		struct cgrp_cset_link *link;
+
+		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
+			struct cgroup *c = link->cgrp;
+
+			if (c->root == root) {
+				res = c;
+				break;
+			}
+		}
+	}
+	rcu_read_unlock();
+
+	BUG_ON(!res);
+	return res;
+}
+
 /* look up cgroup associated with given css_set on the specified hierarchy */
 static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
 					    struct cgroup_root *root)
@@ -1598,13 +1633,11 @@ static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
 {
 	int len = 0, ret = 0;
 	char *buf = NULL;
-	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
 	struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
 	struct cgroup *ns_cgroup;
 
-	mutex_lock(&cgroup_mutex);
 	spin_lock_bh(&css_set_lock);
-	ns_cgroup = cset_cgroup_from_root(ns->root_cset, kf_cgroot);
+	ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
 	len = kernfs_path_from_node(kf_node, ns_cgroup->kn, NULL, 0);
 	if (len > 0)
 		buf = kmalloc(len + 1, GFP_ATOMIC);
@@ -1612,7 +1645,6 @@ static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
 		ret = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, len + 1);
 
 	spin_unlock_bh(&css_set_lock);
-	mutex_unlock(&cgroup_mutex);
 
 	if (len <= 0)
 		return len;
-- 
2.7.4

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#1392370

On Fri, Apr 29, 2016 at 04:42:54PM -0500, Serge E. Hallyn wrote:
> [ I'm sorry, apparently I had sent the wrong version of this patch.  Here
> is the correct one from
> https://git.kernel.org/cgit/linux/kernel/git/sergeh/linux-security.git/commit/?h=2016-04-17/kernfs.show&id=79f784037098fddae92258579ef494537a12f1b2
> Thanks Michael for pointing that out
> ]
> 
> Since we're getting current's cgroup namespace info, and are
> not modifying it, we don't need the cgroup_mutex.
> 
> Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>

Can you please fold this into the previous patch?

Thanks.

-- 
tejun

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#1393449

Quoting Tejun Heo (tj@kernel.org):
> On Fri, Apr 29, 2016 at 04:42:54PM -0500, Serge E. Hallyn wrote:
> > [ I'm sorry, apparently I had sent the wrong version of this patch.  Here
> > is the correct one from
> > https://git.kernel.org/cgit/linux/kernel/git/sergeh/linux-security.git/commit/?h=2016-04-17/kernfs.show&id=79f784037098fddae92258579ef494537a12f1b2
> > Thanks Michael for pointing that out
> > ]
> > 
> > Since we're getting current's cgroup namespace info, and are
> > not modifying it, we don't need the cgroup_mutex.
> > 
> > Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
> 
> Can you please fold this into the previous patch?

Will do, and will add the documentation Michael asked for.  In the
middle of something still today, but will send this out this week.

thanks,
-serge

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