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Subject[PATCH] cls_cgroup: read classid atomically in classifier
Date
cls_cgroup: read classid atomically in classifier

Avoid reading the unsynchronized value cs->classid multiple times,
since it could change concurrently from non-zero to zero; this would
result in the classifier returning a positive result with a bogus
(zero) classid.

Signed-off-by: Paul Menage <menage@google.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>

---

Fixes a whitespace issue from the previous version of the patch

net/sched/cls_cgroup.c | 22 +++++++++++-----------
1 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/net/sched/cls_cgroup.c b/net/sched/cls_cgroup.c
index 1ab4542..0f815cc 100644
--- a/net/sched/cls_cgroup.c
+++ b/net/sched/cls_cgroup.c
@@ -98,8 +98,7 @@ static int cls_cgroup_classify(struct sk_buff *skb, struct tcf_proto *tp,
struct tcf_result *res)
{
struct cls_cgroup_head *head = tp->root;
- struct cgroup_cls_state *cs;
- int ret = 0;
+ u32 classid;

/*
* Due to the nature of the classifier it is required to ignore all
@@ -115,17 +114,18 @@ static int cls_cgroup_classify(struct sk_buff *skb, struct tcf_proto *tp,
return -1;

rcu_read_lock();
- cs = task_cls_state(current);
- if (cs->classid && tcf_em_tree_match(skb, &head->ematches, NULL)) {
- res->classid = cs->classid;
- res->class = 0;
- ret = tcf_exts_exec(skb, &head->exts, res);
- } else
- ret = -1;
-
+ classid = task_cls_state(current)->classid;
rcu_read_unlock();

- return ret;
+ if (!classid)
+ return -1;
+
+ if (!tcf_em_tree_match(skb, &head->ematches, NULL))
+ return -1;
+
+ res->classid = classid;
+ res->class = 0;
+ return tcf_exts_exec(skb, &head->exts, res);
}

static unsigned long cls_cgroup_get(struct tcf_proto *tp, u32 handle)


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