From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Horman Subject: Re: sctp: hang in sctp_remaddr_seq_show Date: Mon, 18 Mar 2013 16:32:02 -0400 Message-ID: <20130318203202.GB9478@hmsreliant.think-freely.org> References: <51434D78.9030308@oracle.com> <20130318110415.GA9478@hmsreliant.think-freely.org> <1363620340.29475.132.camel@edumazet-glaptop> <5147333A.3010907@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Dumazet , Sasha Levin , sri@us.ibm.com, "David S. Miller" , linux-sctp@vger.kernel.org, netdev@vger.kernel.org, Dave Jones , "linux-kernel@vger.kernel.org" To: Vlad Yasevich Return-path: Content-Disposition: inline In-Reply-To: <5147333A.3010907@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, Mar 18, 2013 at 11:31:06AM -0400, Vlad Yasevich wrote: > On 03/18/2013 11:25 AM, Eric Dumazet wrote: > >On Mon, 2013-03-18 at 07:04 -0400, Neil Horman wrote: > > > >>I'm not sure why the process would never get back to the schedule, but looking > >>at the sctp_remaddr_seq_show function, I think that we should convert this > >>sequence: > >> sctp_local_bh_disable(); > >> read_lock(&head->lock); > >> rcu_read_lock(); > >> > >>to this: > >> read_lock(&head->lock); > >> rcu_read_lock_bh(); > >> > >>Neil > > > >I dont think so. > > > >BH needs to be disabled before read_lock(&head->lock); > > > >or else, write_lock() could deadlock (assuming it can be called from BH) > > > > > > If anything, this should probably be done like this: > > rcu_read_lock(); > read_lock_bh(&head->lock) > ... > > read_unlock_bh(&head->lock) > rcu_read_unlock(); > Vlads, right. We need to grab the rcu lock before the read lock, but we should probably use the rcu_read_lock_bh variant, since we're going to disable bottom halves anyway. Neil > -vlad > -- > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >