On Thu, Mar 27, 2014 at 10:44 AM, Flavio Leitner <f...@redhat.com> wrote: > On Thu, Mar 27, 2014 at 10:37:32AM -0700, Jesse Gross wrote: >> On Thu, Mar 27, 2014 at 10:33 AM, Flavio Leitner <f...@redhat.com> wrote: >> > On Thu, Mar 27, 2014 at 10:19:23AM -0700, Pravin Shelar wrote: >> >> On Thu, Mar 27, 2014 at 7:05 AM, Flavio Leitner <f...@redhat.com> wrote: >> >> > There are two problematic situations. >> >> > >> >> > A deadlock can happen when is_percpu is false because it can get >> >> > interrupted while holding the spinlock. Then it executes >> >> > ovs_flow_stats_update() in softirq context which tries to get >> >> > the same lock. >> >> > >> >> > The second sitation is that when is_percpu is true, the code >> >> > correctly disables BH but only for the local CPU, so the >> >> > following can happen when locking the remote CPU without >> >> > disabling BH: >> >> > >> >> > CPU#0 CPU#1 >> >> > ovs_flow_stats_get() >> >> > stats_read() >> >> > +->spin_lock remote CPU#1 ovs_flow_stats_get() >> >> > | <interrupted> stats_read() >> >> > | ... +--> spin_lock remote CPU#0 >> >> > | | <interrupted> >> >> > | ovs_flow_stats_update() | ... >> >> > | spin_lock local CPU#0 <--+ ovs_flow_stats_update() >> >> > +---------------------------------- spin_lock local CPU#1 >> >> > >> >> > This patch disables BH for both cases fixing the deadlocks. >> >> >> >> This bug is already fixed in OVS. >> > >> > Could you point me to the commit? I am not finding anything >> > recent. >> >> This is the commit: >> >> commit 9d73c9cac76ba557fdac4a89c1b7eafe132b85a3 >> Author: Pravin B Shelar <pshe...@nicira.com> >> Date: Tue Dec 17 15:43:30 2013 -0800 >> >> datapath: Fix deadlock during stats update. >> >> I thought that I had sent it in the most recent batch of changes for >> net but it looks like I missed it. > > That commit is incomplete. Look at the scenario #2 which I explain > why it is needed to disable bh for all cpus and not just local ones.
OK, I understand the second problem now. OVS master (which I am currently working to cross-port to net-next) uses a different strategy that also always disables bottom halves for a different reason. Since I forgot to send the original patch, maybe we can just apply this one to net instead and use the new stuff directly everywhere else. Pravin, any objections? _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
