From: Jarek Poplawski <jarkao2@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
David Miller <davem@davemloft.net>,
linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH] net: fix a lockdep splat
Date: Thu, 23 Sep 2010 00:13:19 +0200 [thread overview]
Message-ID: <4C9A7F7F.5010507@gmail.com> (raw)
In-Reply-To: <1285184088.2380.18.camel@edumazet-laptop>
Eric Dumazet wrote:
> [PATCH] net: fix a lockdep splat
>
> We have for each socket :
>
> One spinlock (sk_slock.slock)
> One rwlock (sk_callback_lock)
>
> Possible scenarios are :
>
> (A) (this is used in net/sunrpc/xprtsock.c)
> read_lock(&sk->sk_callback_lock) (without blocking BH)
> <BH>
> spin_lock(&sk->sk_slock.slock);
> ...
> read_lock(&sk->sk_callback_lock);
> ...
>
>
> (B)
> write_lock_bh(&sk->sk_callback_lock)
> stuff
> write_unlock_bh(&sk->sk_callback_lock)
>
>
> (C)
> spin_lock_bh(&sk->sk_slock)
> ...
> write_lock_bh(&sk->sk_callback_lock)
> stuff
> write_unlock_bh(&sk->sk_callback_lock)
> spin_unlock_bh(&sk->sk_slock)
>
> This (C) case conflicts with (A) :
>
> CPU1 [A] CPU2 [C]
> read_lock(callback_lock)
> <BH> spin_lock_bh(slock)
> <wait to spin_lock(slock)>
> <wait to write_lock_bh(callback_lock)>
>
> We have one problematic (C) use case in inet_csk_listen_stop() :
>
> local_bh_disable();
> bh_lock_sock(child); // spin_lock_bh(&sk->sk_slock)
> WARN_ON(sock_owned_by_user(child));
> ...
> sock_orphan(child); // write_lock_bh(&sk->sk_callback_lock)
>
> lockdep is not happy with this, as reported by Tetsuo Handa
>
> This patch makes sure inet_csk_listen_stop() uses following lock order :
>
> write_lock_bh(&sk->sk_callback_lock)
> spin_lock(&sk->sk_slock)
> ...
> spin_unlock(&sk->sk_slock)
> write_unlock_bh(&sk->sk_callback_lock)
IMHO this order conflicts with (A) too (but I'm not sure lockdep
tracks that):
CPU1 [A] CPU2 [C-reversed]
... write_lock_bh(callback_lock)
<BH>
spin_lock(slock)
<wait to spin_lock(slock)>
<wait to read_lock(callback_lock)>
My proposal is to BH protect read_lock(sk_callback_lock) everywhere (it's
done by netfilter in a few places already).
Jarek P.
next prev parent reply other threads:[~2010-09-22 22:13 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-24 11:53 [2.6.35-rc3] NFS: possible irq lock inversion dependency Tetsuo Handa
2010-09-07 12:32 ` [2.6.36-rc3] " Tetsuo Handa
2010-09-21 6:51 ` [2.6.35-rc5] INET?: " Tetsuo Handa
2010-09-21 7:56 ` Eric Dumazet
2010-09-21 9:10 ` [2.6.36-rc5] " Tetsuo Handa
2010-09-21 9:35 ` Eric Dumazet
2010-09-21 10:13 ` Eric Dumazet
2010-09-22 7:14 ` Tetsuo Handa
2010-09-22 8:31 ` Eric Dumazet
2010-09-22 8:34 ` Eric Dumazet
2010-09-22 8:38 ` Eric Dumazet
2010-09-22 8:58 ` Tetsuo Handa
2010-09-22 17:35 ` Eric Dumazet
2010-09-22 19:34 ` [PATCH] net: fix a lockdep splat Eric Dumazet
2010-09-22 20:33 ` David Miller
2010-09-22 22:13 ` Jarek Poplawski [this message]
2010-09-22 22:43 ` Eric Dumazet
2010-09-23 3:53 ` David Miller
2010-09-23 4:23 ` David Miller
2010-09-23 5:05 ` Eric Dumazet
2010-09-23 5:42 ` Eric Dumazet
2010-09-23 6:32 ` Tetsuo Handa
2010-09-23 6:44 ` Eric Dumazet
2010-09-25 5:26 ` David Miller
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