From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net-next] packet: Protect packet sk list with mutex (v2) Date: Wed, 22 Aug 2012 08:59:17 +0200 Message-ID: <1345618757.5158.612.camel@edumazet-glaptop> References: <50336BC7.7030209@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: David Miller , Linux Netdev List To: Pavel Emelyanov Return-path: Received: from mail-bk0-f46.google.com ([209.85.214.46]:51573 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752698Ab2HVG7W (ORCPT ); Wed, 22 Aug 2012 02:59:22 -0400 Received: by bkwj10 with SMTP id j10so169807bkw.19 for ; Tue, 21 Aug 2012 23:59:21 -0700 (PDT) In-Reply-To: <50336BC7.7030209@parallels.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2012-08-21 at 15:06 +0400, Pavel Emelyanov wrote: > Change since v1: > > * Fixed inuse counters access spotted by Eric > > In patch eea68e2f (packet: Report socket mclist info via diag module) I've > introduced a "scheduling in atomic" problem in packet diag module -- the > socket list is traversed under rcu_read_lock() while performed under it sk > mclist access requires rtnl lock (i.e. -- mutex) to be taken. > > [152363.820563] BUG: scheduling while atomic: crtools/12517/0x10000002 > [152363.820573] 4 locks held by crtools/12517: > [152363.820581] #0: (sock_diag_mutex){+.+.+.}, at: [] sock_diag_rcv+0x1f/0x3e > [152363.820613] #1: (sock_diag_table_mutex){+.+.+.}, at: [] sock_diag_rcv_msg+0xdb/0x11a > [152363.820644] #2: (nlk->cb_mutex){+.+.+.}, at: [] netlink_dump+0x23/0x1ab > [152363.820693] #3: (rcu_read_lock){.+.+..}, at: [] packet_diag_dump+0x0/0x1af > > Similar thing was then re-introduced by further packet diag patches (fanount > mutex and pgvec mutex for rings) :( > > Apart from being terribly sorry for the above, I propose to change the packet > sk list protection from spinlock to mutex. This lock currently protects two > modifications: > > * sklist > * prot inuse counters > > The sklist modifications can be just reprotected with mutex since they already > occur in a sleeping context. The inuse counters modifications are trickier -- the > __this_cpu_-s are used inside, thus requiring the caller to handle the potential > issues with contexts himself. Since packet sockets' counters are modified in two > places only (packet_create and packet_release) we only need to protect the context > from being preempted. BH disabling is not required in this case. > > Signed-off-by: Pavel Emelyanov > > --- > > diff --git a/include/net/netns/packet.h b/include/net/netns/packet.h > index cb4e894..4780b08 100644 > --- a/include/net/netns/packet.h > +++ b/include/net/netns/packet.h > @@ -8,7 +8,7 @@ > #include > > struct netns_packet { > - spinlock_t sklist_lock; > + struct mutex sklist_lock; > struct hlist_head sklist; > }; > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index 226b2cd..79bc69c 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -2308,10 +2308,13 @@ static int packet_release(struct socket *sock) > net = sock_net(sk); > po = pkt_sk(sk); > > - spin_lock_bh(&net->packet.sklist_lock); > + mutex_lock(&net->packet.sklist_lock); > sk_del_node_init_rcu(sk); > + mutex_unlock(&net->packet.sklist_lock); I am still a bit uncomfortable : are we allowed to sleep in a release() handler ? It seems yes, so : Acked-by: Eric Dumazet