netdev - Re: [PATCH net-next] net: sched: flower: refactor reoffload for concurrent access

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Message-ID: <20190423095131.41383446@cakuba.netronome.com>
Date:   Tue, 23 Apr 2019 09:51:31 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH net-next] net: sched: flower: refactor reoffload for
 concurrent access

On Tue, 23 Apr 2019 07:34:20 +0000, Vlad Buslov wrote:
> >> @@ -382,6 +395,8 @@ static void fl_hw_destroy_filter(struct tcf_proto *tp, struct cls_fl_filter *f,
> >>  
> >>  	tc_setup_cb_call(block, TC_SETUP_CLSFLOWER, &cls_flower, false);
> >>  	spin_lock(&tp->lock);
> >> +	if (!list_empty(&f->hw_list))
> >> +		list_del_init(&f->hw_list);  
> >
> > Mm. I thought list_del_init() on an empty list should be fine?  
> 
> Is it? Implementation of list_del_init() doesn't seem to check if list
> is empty before re-initializing its pointers. Technically it seems like
> it can work because the implementation will just set pointers of empty
> list to point to itself (which is how empty list head is defined), but
> should we assume this is intended behavior and not just implementation
> detail? I don't see anything in comments for this function that suggests
> that it is okay to call list_del_init() on empty list head.

Mm.. I'd do it, IDK if there was ever an official ruling by the
supreme court of Linus or any such ;)  __list_del_entry_valid() 
looks like it'd not complain.  Up to you, in general it didn't 
read very idiomatic, that's all.