Re: [PATCH 10/14] net: sched: extend act API for lockless actions

Jiri Pirko
2018-05-16T08:56:35Z

Wed, May 16, 2018 at 10:16:13AM CEST, vladbu@mellanox.com wrote:
>
>On Wed 16 May 2018 at 07:50, Jiri Pirko <jiri@resnulli.us> wrote:
>> Mon, May 14, 2018 at 04:27:11PM CEST, vladbu@mellanox.com wrote:
>>>Implement new action API function to atomically delete action with
>>>specified index and to atomically insert unique action. These functions are
>>>required to implement init and delete functions for specific actions that
>>>do not rely on rtnl lock.
>>>
>>>Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
>>>---
>>> include/net/act_api.h | 2 ++
>>> net/sched/act_api.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>>> 2 files changed, 47 insertions(+)
>>>
>>>diff --git a/include/net/act_api.h b/include/net/act_api.h
>>>index a8c8570..bce0cf1 100644
>>>--- a/include/net/act_api.h
>>>+++ b/include/net/act_api.h
>>>@@ -153,7 +153,9 @@ int tcf_idr_create(struct tc_action_net *tn, u32 index, struct nlattr *est,
>>> struct tc_action **a, const struct tc_action_ops *ops,
>>> int bind, bool cpustats);
>>> void tcf_idr_insert(struct tc_action_net *tn, struct tc_action *a);
>>>+void tcf_idr_insert_unique(struct tc_action_net *tn, struct tc_action *a);
>>>
>>>+int tcf_idr_find_delete(struct tc_action_net *tn, u32 index);
>>> int __tcf_idr_release(struct tc_action *a, bool bind, bool strict);
>>>
>>> static inline int tcf_idr_release(struct tc_action *a, bool bind)
>>>diff --git a/net/sched/act_api.c b/net/sched/act_api.c
>>>index 2772276e..a5193dc 100644
>>>--- a/net/sched/act_api.c
>>>+++ b/net/sched/act_api.c
>>>@@ -330,6 +330,41 @@ bool tcf_idr_check(struct tc_action_net *tn, u32 index, struct tc_action **a,
>>> }
>>> EXPORT_SYMBOL(tcf_idr_check);
>>>
>>>+int tcf_idr_find_delete(struct tc_action_net *tn, u32 index)
>>>+{
>>>+ struct tcf_idrinfo *idrinfo = tn->idrinfo;
>>>+ struct tc_action *p;
>>>+ int ret = 0;
>>>+
>>>+ spin_lock_bh(&idrinfo->lock);
>>
>> Why "_bh" is needed here?
>
>Original idr remove function used _bh version so I used it here as well.
>As I already replied to your previous question about idrinfo lock usage,
>I don't see any particular reason for locking with _bh at this point.
>I've contacted the author(Chris Mi) and he said that he just preserved
>locking the same way as it was before he changed hash table to idr for
>action lookup.
>
>You want me to do standalone patch that cleans up idrinfo locking?

Yes please. You can send it separately, not as a part of this patchset.

>
>>
>>
>>>+ p = idr_find(&idrinfo->action_idr, index);
>>>+ if (!p) {
>>>+ spin_unlock(&idrinfo->lock);
>>>+ return -ENOENT;
>>>+ }
>>>+
>>>+ if (!atomic_read(&p->tcfa_bindcnt)) {
>>>+ if (refcount_dec_and_test(&p->tcfa_refcnt)) {
>>>+ struct module *owner = p->ops->owner;
>>>+
>>>+ WARN_ON(p != idr_remove(&idrinfo->action_idr,
>>>+ p->tcfa_index));
>>>+ spin_unlock_bh(&idrinfo->lock);
>>>+
>>>+ tcf_action_cleanup(p);
>>>+ module_put(owner);
>>>+ return 0;
>>>+ }
>>>+ ret = 0;
>>>+ } else {
>>>+ ret = -EPERM;
>>
>> I wonder if "-EPERM" is the best error code for this...
>
>This is what original code returned so I decided to preserve
>compatibility.

Okay.

>
>>
>>
>>>+ }
>>>+
>>>+ spin_unlock_bh(&idrinfo->lock);
>>>+ return ret;
>>>+}
>>>+EXPORT_SYMBOL(tcf_idr_find_delete);
>>>+
>>> int tcf_idr_create(struct tc_action_net *tn, u32 index, struct nlattr *est,
>>> struct tc_action **a, const struct tc_action_ops *ops,
>>> int bind, bool cpustats)
>>>@@ -407,6 +442,16 @@ void tcf_idr_insert(struct tc_action_net *tn, struct tc_action *a)
>>> }
>>> EXPORT_SYMBOL(tcf_idr_insert);
>>>
>>>+void tcf_idr_insert_unique(struct tc_action_net *tn, struct tc_action *a)
>>>+{
>>>+ struct tcf_idrinfo *idrinfo = tn->idrinfo;
>>>+
>>>+ spin_lock_bh(&idrinfo->lock);
>>>+ WARN_ON(idr_replace(&idrinfo->action_idr, a, a->tcfa_index));
>>
>> Under which condition this WARN_ON is hit?
>
>When idr replace returns non-NULL pointer, which means that somehow
>concurrent insertion of action with same index has happened and we are
>leaking memory.

Is that possible to happen? Meaning, can I as a user cause this by doing
something in a wrong/unexpected way?

>
>By the way I'm still not sure if having this insert unique function is
>warranted or I should just add WARN to regular idr insert. What is your
>opinion on this?

I have to check where you use this.

>
>>
>>
>>>+ spin_unlock_bh(&idrinfo->lock);
>>>+}
>>>+EXPORT_SYMBOL(tcf_idr_insert_unique);
>>>+
>>> void tcf_idrinfo_destroy(const struct tc_action_ops *ops,
>>> struct tcf_idrinfo *idrinfo)
>>> {
>>>--
>>>2.7.5
>>>
>