netdev - Re: [PATCH v2 net-next] net: hsr: fix suspicious usage in hsr_node_get

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Date:   Thu, 10 Feb 2022 09:47:44 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Juhee Kang <claudiajkang@...il.com>, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org
Cc:     ennoerlangen@...il.com, george.mccollister@...il.com,
        olteanv@...il.com, marco.wenzel@...berle.de,
        syzbot+f0eb4f3876de066b128c@...kaller.appspotmail.com
Subject: Re: [PATCH v2 net-next] net: hsr: fix suspicious usage in
 hsr_node_get_first()


On 2/10/22 08:23, Juhee Kang wrote:
> Currently, to dereference hlist_node which is result of hlist_first_rcu(),
> rcu_dereference() is used. But, suspicious RCU warnings occur because
> the caller doesn't acquire RCU. So it was solved by adding rcu_read_lock().
>
> The kernel test robot reports:
>      [   53.750001][ T3597] =============================
>      [   53.754849][ T3597] WARNING: suspicious RCU usage
>      [   53.759833][ T3597] 5.17.0-rc2-syzkaller-00903-g45230829827b #0 Not tainted
>      [   53.766947][ T3597] -----------------------------
>      [   53.771840][ T3597] net/hsr/hsr_framereg.c:34 suspicious rcu_dereference_check() usage!
>      [   53.780129][ T3597] other info that might help us debug this:
>      [   53.790594][ T3597] rcu_scheduler_active = 2, debug_locks = 1
>      [   53.798896][ T3597] 2 locks held by syz-executor.0/3597:


Please include whole stack.


>
> Fixes: 4acc45db7115 ("net: hsr: use hlist_head instead of list_head for mac addresses")
> Reported-by: Eric Dumazet <eric.dumazet@...il.com>
> Reported-by: syzbot+f0eb4f3876de066b128c@...kaller.appspotmail.com
> Signed-off-by: Juhee Kang <claudiajkang@...il.com>
> ---
> v2:
>   - rebase current net-next tree
>
>   net/hsr/hsr_framereg.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/net/hsr/hsr_framereg.c b/net/hsr/hsr_framereg.c
> index b3c6ffa1894d..92abdf855327 100644
> --- a/net/hsr/hsr_framereg.c
> +++ b/net/hsr/hsr_framereg.c
> @@ -31,7 +31,10 @@ struct hsr_node *hsr_node_get_first(struct hlist_head *head)
>   {
>   	struct hlist_node *first;
>   
> +	rcu_read_lock();
>   	first = rcu_dereference(hlist_first_rcu(head));
> +	rcu_read_unlock();
> +
>   	if (first)
>   		return hlist_entry(first, struct hsr_node, mac_list);
>   


This is not fixing anything, just silence the warning.