netdev - Re: [PATCH net-next] sctp: avoid list_del_init if it's freeing the memory right away

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Message-Id: <20170207.142121.1027174926882132252.davem@davemloft.net>
Date:   Tue, 07 Feb 2017 14:21:21 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     marcelo.leitner@...il.com
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        vyasevich@...il.com, nhorman@...driver.com
Subject: Re: [PATCH net-next] sctp: avoid list_del_init if it's freeing the
 memory right away

From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Date: Tue,  7 Feb 2017 17:03:21 -0200

> There is no reason to use list_del_init() in these places as we are
> going to free/destroy the memory in a few lines below.
> 
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> ---
>  net/sctp/associola.c     | 14 ++++----------
>  net/sctp/auth.c          |  8 ++------
>  net/sctp/chunk.c         |  4 ++--
>  net/sctp/outqueue.c      | 14 +++++++-------
>  net/sctp/sm_make_chunk.c |  3 +--
>  5 files changed, 16 insertions(+), 27 deletions(-)
> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index e50dc6d7543fd6acfa7442f3a9ee575203c7718d..7eb9dacfa53a438b20a34319cf01c6c9a591f0c3 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1638,25 +1638,19 @@ int sctp_assoc_set_id(struct sctp_association *asoc, gfp_t gfp)
>  static void sctp_assoc_free_asconf_queue(struct sctp_association *asoc)
>  {
>  	struct sctp_chunk *asconf;
> -	struct sctp_chunk *tmp;
>  
> -	list_for_each_entry_safe(asconf, tmp, &asoc->addip_chunk_list, list) {
> -		list_del_init(&asconf->list);
> +	list_for_each_entry(asconf, &asoc->addip_chunk_list, list)
>  		sctp_chunk_free(asconf);
> -	}
>  }

This leave freed memory on the asoc->addip_chunk_list, in fact why aren't you seeing
the BUG_ON() in sctp_chunk_destroy() get triggered?  If you elide the list_del() here
then the "list_empty(&chunk->list)" check there will not be true.

I don't think this transformation here is legal at all.