netdev - Re: [PATCH net-next v7 5/6] flow_offload: support get multi-subsystem block

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Date:   Fri, 16 Aug 2019 10:56:27 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     wenxu <wenxu@...oud.cn>, David Miller <davem@...emloft.net>,
        Jiri Pirko <jiri@...nulli.us>,
        "pablo@...filter.org" <pablo@...filter.org>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v7 5/6] flow_offload: support get
 multi-subsystem block

On Fri, 16 Aug 2019 15:04:44 +0000, Vlad Buslov wrote:
> >> [  401.511871] RSP: 002b:00007ffca2a9fad8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> >> [  401.511875] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007fad892d30f8
> >> [  401.511878] RDX: 0000000000000002 RSI: 000055afeb072a90 RDI: 0000000000000001
> >> [  401.511881] RBP: 000055afeb072a90 R08: 00000000ffffffff R09: 000000000000000a
> >> [  401.511884] R10: 000055afeb058710 R11: 0000000000000246 R12: 0000000000000002
> >> [  401.511887] R13: 00007fad893a8780 R14: 0000000000000002 R15: 00007fad893a3740
> >>
> >> I don't think it is correct approach to try to call these callbacks with
> >> rcu protection because:
> >>
> >> - Cls API uses sleeping locks that cannot be used in rcu read section
> >>   (hence the included trace).
> >>
> >> - It assumes that all implementation of classifier ops reoffload() don't
> >>   sleep.
> >>
> >> - And that all driver offload callbacks (both block and classifier
> >>   setup) don't sleep, which is not the case.
> >>
> >> I don't see any straightforward way to fix this, besides using some
> >> other locking mechanism to protect block_ing_cb_list.
> >>
> >> Regards,
> >> Vlad  
> >
> > Maybe get the  mutex flow_indr_block_ing_cb_lock for both lookup, add, delete? 
> >
> > the callbacks_lists. the add and delete is work only on modules init case. So the
> >
> > lookup is also not frequently(ony [un]register) and can protect with the locks.  
> 
> That should do the job. I'll send the patch.

Hi Vlad! 

While looking into this, would you mind also add the missing
flow_block_cb_is_busy() calls in the indirect handlers in the drivers?

LMK if you're too busy, I don't want this to get forgotten :)