netdev - Re: [PATCH net 1/3] taprio: Fix kernel panic in taprio

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Message-Id: <20190829.170748.656667843147010952.davem@davemloft.net>
Date:   Thu, 29 Aug 2019 17:07:48 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     olteanv@...il.com
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        vinicius.gomes@...el.com, vedang.patel@...el.com,
        leandro.maciel.dorileo@...el.com, netdev@...r.kernel.org
Subject: Re: [PATCH net 1/3] taprio: Fix kernel panic in taprio_destroy

From: Vladimir Oltean <olteanv@...il.com>
Date: Wed, 28 Aug 2019 17:48:27 +0300

> taprio_init may fail earlier than this line:
> 
> 	list_add(&q->taprio_list, &taprio_list);
> 
> i.e. due to the net device not being multi queue.
> 
> Attempting to remove q from the global taprio_list when it is not part
> of it will result in a kernel panic.
> 
> Fix it by iterating through the list and removing it only if found.
> 
> Signed-off-by: Vladimir Oltean <olteanv@...il.com>

I don't like this solution for two reaons, I think it's actually
error prone, and now every taprio_destroy() eats the cost of traversing
the entire list.

The whole reason to use a list head is O(1) removal.

Just init the list head early in the creation then the list_del() just
works.