From: Jakub Kicinski <kuba@kernel.org>
To: Amol Grover <frextrite@gmail.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
linux-kernel-mentees@lists.linuxfoundation.org,
"David S . Miller" <davem@davemloft.net>
Subject: Re: [Linux-kernel-mentees] [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro
Date: Sat, 9 May 2020 14:19:38 -0700 [thread overview]
Message-ID: <20200509141938.028fa959@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <20200509072243.3141-2-frextrite@gmail.com>
On Sat, 9 May 2020 12:52:44 +0530 Amol Grover wrote:
> ipmr_for_each_table() uses list_for_each_entry_rcu() for
> traversing outside of an RCU read-side critical section but
> under the protection of pernet_ops_rwsem. Hence add the
> corresponding lockdep expression to silence the following
> false-positive warning at boot:
Thanks for the fix, the warning has been annoying me as well!
> [ 0.645292] =============================
> [ 0.645294] WARNING: suspicious RCU usage
> [ 0.645296] 5.5.4-stable #17 Not tainted
> [ 0.645297] -----------------------------
> [ 0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
please provide a fuller stack trace, it would have helped the review
> Signed-off-by: Amol Grover <frextrite@gmail.com>
> ---
> net/ipv4/ipmr.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> index 99c864eb6e34..950ffe9943da 100644
> --- a/net/ipv4/ipmr.c
> +++ b/net/ipv4/ipmr.c
> @@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags);
> static void ipmr_expire_process(struct timer_list *t);
>
> #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
> -#define ipmr_for_each_table(mrt, net) \
> - list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
> - lockdep_rtnl_is_held())
> +#define ipmr_for_each_table(mrt, net) \
> + list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
> + lockdep_rtnl_is_held() || \
> + lockdep_is_held(&pernet_ops_rwsem))
This is a strange condition, IMHO. How can we be fine with either
lock.. This is supposed to be the writer side lock, one can't have
two writer side locks..
I think what is happening is this:
ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()
ipmr_new_table() returns an existing table if there is one, but
obviously none can exist at init. So a better fix would be:
#define ipmr_for_each_table(mrt, net) \
list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
lockdep_rtnl_is_held() || \
list_empty(&net->ipv4.mr_tables))
Thoughts?
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees
next prev parent reply other threads:[~2020-05-09 21:19 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-09 7:22 [Linux-kernel-mentees] [PATCH net 1/2 RESEND] ipmr: Fix RCU list debugging warning Amol Grover
2020-05-09 7:22 ` [Linux-kernel-mentees] [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro Amol Grover
2020-05-09 21:19 ` Jakub Kicinski [this message]
2020-05-12 5:17 ` Madhuparna Bhowmik
2020-05-12 16:32 ` Jakub Kicinski
2020-05-13 5:34 ` Madhuparna Bhowmik
2020-05-12 17:17 ` Amol Grover
2020-05-12 21:59 ` Jakub Kicinski
2020-05-13 11:54 ` Stephen Rothwell
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200509141938.028fa959@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com \
--to=kuba@kernel.org \
--cc=davem@davemloft.net \
--cc=frextrite@gmail.com \
--cc=joel@joelfernandes.org \
--cc=kuznet@ms2.inr.ac.ru \
--cc=linux-kernel-mentees@lists.linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=madhuparnabhowmik10@gmail.com \
--cc=netdev@vger.kernel.org \
--cc=paulmck@kernel.org \
--cc=yoshfuji@linux-ipv6.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).