netdev - Re: [PATCH net] decnet: always not take dst->__refcnt when inserting dst into hash table

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Message-Id: <20170616.150027.1514023118759756329.davem@davemloft.net>
Date:   Fri, 16 Jun 2017 15:00:27 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     tracywwnj@...il.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, kafai@...com,
        weiwan@...gle.com
Subject: Re: [PATCH net] decnet: always not take dst->__refcnt when
 inserting dst into hash table

From: Wei Wang <tracywwnj@...il.com>
Date: Fri, 16 Jun 2017 10:46:37 -0700

> From: Wei Wang <weiwan@...gle.com>
> 
> In the existing dn_route.c code, dn_route_output_slow() takes
> dst->__refcnt before calling dn_insert_route() while dn_route_input_slow()
> does not take dst->__refcnt before calling dn_insert_route().
> This makes the whole routing code very buggy.
> In dn_dst_check_expire(), dnrt_free() is called when rt expires. This
> makes the routes inserted by dn_route_output_slow() not able to be
> freed as the refcnt is not released.
> In dn_dst_gc(), dnrt_drop() is called to release rt which could
> potentially cause the dst->__refcnt to be dropped to -1.
> In dn_run_flush(), dst_free() is called to release all the dst. Again,
> it makes the dst inserted by dn_route_output_slow() not able to be
> released and also, it does not wait on the rcu and could potentially
> cause crash in the path where other users still refer to this dst.
> 
> This patch makes sure both input and output path do not take
> dst->__refcnt before calling dn_insert_route() and also makes sure
> dnrt_free()/dst_free() is called when removing dst from the hash table.
> The only difference between those 2 calls is that dnrt_free() waits on
> the rcu while dst_free() does not.
> 
> Signed-off-by: Wei Wang <weiwan@...gle.com>
> Acked-by: Martin KaFai Lau <kafai@...com>

Applied and queued up for -stable, thanks.

I've also applied it to net-next for the sake of your dst gc removal
series.

Thanks again.