On Wed 17 Apr 2019 at 19:34, Jakub Kicinski <jakub.kicin...@netronome.com> wrote: > On Wed, 17 Apr 2019 07:29:36 +0000, Vlad Buslov wrote: >> On Wed 17 Apr 2019 at 00:49, Jakub Kicinski <jakub.kicin...@netronome.com> >> wrote: >> > On Tue, 16 Apr 2019 17:20:47 +0300, Vlad Buslov wrote: >> >> @@ -1551,6 +1558,10 @@ static int fl_change(struct net *net, struct >> >> sk_buff *in_skb, >> >> goto errout_mask; >> >> >> >> if (!tc_skip_hw(fnew->flags)) { >> >> + spin_lock(&tp->lock); >> >> + list_add(&fnew->hw_list, &head->hw_filters); >> >> + spin_unlock(&tp->lock); >> >> + >> >> err = fl_hw_replace_filter(tp, fnew, rtnl_held, extack); >> >> if (err) >> >> goto errout_ht; >> > >> > Duplicated deletes should be fine, but I'm not sure same is true for >> > adds. Won't seeing an add with the same cookie twice confuse drivers? >> > >> > There's also the minor issue of offloaded count being off in that >> > case :) >> >> Hmmm, okay. Rejecting duplicate cookies should be a trivial change to >> drivers though. Do you see any faults with this approach in general? > > Trivial or not it adds up, the stack should make driver authors' job as > easy as possible. The simplest thing to do would be to add a mutex > around the HW calls. But that obviously doesn't work for you, cause > you want multiple outstanding requests to the FW for a single tp, right? > > How about a RW lock, that would take R on normal add/replace/del paths > and W on replays? That should scale, no?
I've been thinking some more about possible ways to mitigate the problem. First of all I tried to implement POC of rwlock in flower and it isn't straightforward because of lock ordering. Observe that fl_reoffload() is always called with rtnl lock taken (I didn't do any work to unlock bind/unbind), but fl_change() can be called without rtnl lock and needs to obtain it before offloading rules. This means that we have deadlock here, if fl_change() obtains locks in order rwlock ---> rtnl_lock and fl_reoffload() obtains locks in order rtnl_lock ---> rwlock. Considering this, I tried to improve my solution to remove possibility of multiple adds of same filter and it seems to me that it would be enough to move hw_filters list management in flower offloads functions: add filter to list while holding rtnl lock in fl_hw_replace_filter() and remove it from list while holding rtnl lock in fl_hw_destroy_filter(). What do you think?