linux-kernel - Re: [PATCH net] ipv6: Fix suspicious RCU usage warning in ip6mr

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Date:   Thu, 14 May 2020 09:40:08 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     madhuparnabhowmik10@...il.com
Cc:     davem@...emloft.net, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        sfr@...b.auug.org.au, frextrite@...il.com, joel@...lfernandes.org,
        paulmck@...nel.org, cai@....pw
Subject: Re: [PATCH net] ipv6: Fix suspicious RCU usage warning in ip6mr

On Thu, 14 May 2020 12:32:04 +0530 madhuparnabhowmik10@...il.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> 
> This patch fixes the following warning:
> 
> =============================
> WARNING: suspicious RCU usage
> 5.7.0-rc4-next-20200507-syzkaller #0 Not tainted
> -----------------------------
> net/ipv6/ip6mr.c:124 RCU-list traversed in non-reader section!!
> 
> ipmr_new_table() returns an existing table, but there is no table at
> init. Therefore the condition: either holding rtnl or the list is empty
> is used.
> 
> Fixes: d13fee049f ("Default enable RCU list lockdep debugging with .."): WARNING: suspicious RCU usage

	Fixes tag: Fixes: d13fee049f ("Default enable RCU list lockdep debugging with .."): WARNING: suspicious RCU usage
	Has these problem(s):
		- Target SHA1 does not exist

I think the message at the end is confusing automation, could you use
the standard Fixes tag format, please?

> Reported-by: kernel test robot <lkp@...el.com>
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> ---
>  net/ipv6/ip6mr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
> index 65a54d74acc1..fbe282bb8036 100644
> --- a/net/ipv6/ip6mr.c
> +++ b/net/ipv6/ip6mr.c
> @@ -98,7 +98,7 @@ static void ipmr_expire_process(struct timer_list *t);
>  #ifdef CONFIG_IPV6_MROUTE_MULTIPLE_TABLES
>  #define ip6mr_for_each_table(mrt, net) \
>  	list_for_each_entry_rcu(mrt, &net->ipv6.mr6_tables, list, \
> -				lockdep_rtnl_is_held())
> +				lockdep_rtnl_is_held() ||  list_empty(&net->ipv6.mr6_tables))

double space, line over 80 chars

>  static struct mr_table *ip6mr_mr_table_iter(struct net *net,
>  					    struct mr_table *mrt)

Other than these nits looks good, thanks!