linux-kernel - Re: [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each

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Date:   Thu, 14 May 2020 18:01:32 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     frextrite@...il.com
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org, kuba@...nel.org,
        kaber@...sh.net, sfr@...b.auug.org.au, cai@....pw,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        joel@...lfernandes.org, madhuparnabhowmik10@...il.com,
        paulmck@...nel.org,
        syzbot+1519f497f2f9f08183c6@...kaller.appspotmail.com
Subject: Re: [PATCH net v2 2/2] ipmr: Add lockdep expression to
 ipmr_for_each_table macro

From: Amol Grover <frextrite@...il.com>
Date: Thu, 14 May 2020 23:31:03 +0530

> During the initialization process, ipmr_new_table() is called
> to create new tables which in turn calls ipmr_get_table() which
> traverses net->ipv4.mr_tables without holding the writer lock.
> However, this is safe to do so as no tables exist at this time.
> Hence add a suitable lockdep expression to silence the following
> false-positive warning:
> 
> =============================
> WARNING: suspicious RCU usage
> 5.7.0-rc3-next-20200428-syzkaller #0 Not tainted
> -----------------------------
> net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
> 
> ipmr_get_table+0x130/0x160 net/ipv4/ipmr.c:136
> ipmr_new_table net/ipv4/ipmr.c:403 [inline]
> ipmr_rules_init net/ipv4/ipmr.c:248 [inline]
> ipmr_net_init+0x133/0x430 net/ipv4/ipmr.c:3089
> 
> Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
> Reported-by: syzbot+1519f497f2f9f08183c6@...kaller.appspotmail.com
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Amol Grover <frextrite@...il.com>

Applied.