Re: [Qemu-devel] [PATCH COLO-Frame v11 27/39] COLO failover: Shutdown related socket fd when do failover

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Hailiang Zhang (zhang.zhanghailiang@huawei.com) wrote:
> On 2015/12/11 4:03, Dr. David Alan Gilbert wrote:
> >* zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
> >>If the net connection between COLO's two sides is broken while colo/colo incoming
> >>thread is blocked in 'read'/'write' socket fd. It will not detect this error until
> >>connect timeout. It will be a long time.
> >>
> >>Here we shutdown all the related socket file descriptors to wake up the blocking
> >>operation in failover BH. Besides, we should close the corresponding file descriptors
> >>after failvoer BH shutdown them, or there will be an error.
> >>
> >>Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> >>Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> >>---
> >>v11:
> >>- Only shutdown fd for once
> >>---
> >>  migration/colo.c | 31 +++++++++++++++++++++++++++++--
> >>  1 file changed, 29 insertions(+), 2 deletions(-)
> >>
> >>diff --git a/migration/colo.c b/migration/colo.c
> >>index 4cd7b00..994b80d 100644
> >>--- a/migration/colo.c
> >>+++ b/migration/colo.c
> >>@@ -68,6 +68,14 @@ static void secondary_vm_do_failover(void)
> >>          /* recover runstate to normal migration finish state */
> >>          autostart = true;
> >>      }
> >>+    /*
> >>+    * Make sure colo incoming thread not block in recv,
> >>+    * mis->from_src_file and mis->to_src_file use the same fd,
> >>+    * so here we only need to shutdown it for once.
> >>+    */
> >
> >That assumption is only valid for the current socket transport;
> >for example I have a (partially-working) RDMA transport where the
> >forward and reverse paths are quite separate.
> >
> 
> Yes, you are right, but we really catch the bad stuck case in test for many times,
> and it is easy to reproduce. So i think it's necessary to keep this codes.

Yes, I agree you must shutdown from_src_file, but I mean do you also need to
shutdown to_src_file ?  On sockets they share an fd, but that might not always be
true, so you might have to shutdown both QEMUFile's - but only if you can
get blocked on them.

> 
> >>+    if (mis->from_src_file) {
> >>+        qemu_file_shutdown(mis->from_src_file);
> >>+    }
> >>
> >>      old_state = failover_set_state(FAILOVER_STATUS_HANDLING,
> >>                                     FAILOVER_STATUS_COMPLETED);
> >>@@ -92,6 +100,15 @@ static void primary_vm_do_failover(void)
> >>                            MIGRATION_STATUS_COMPLETED);
> >>      }
> >>
> >>+    /*
> >>+    * Make sure colo thread no block in recv,
> >>+    * Besides, s->rp_state.from_dst_file and s->to_dst_file use the
> >>+    * same fd, so here we only need to shutdown it for once.
> >>+    */
> >>+    if (s->to_dst_file) {
> >>+        qemu_file_shutdown(s->to_dst_file);
> >>+    }
> >>+
> >>      old_state = failover_set_state(FAILOVER_STATUS_HANDLING,
> >>                                     FAILOVER_STATUS_COMPLETED);
> >>      if (old_state != FAILOVER_STATUS_HANDLING) {
> >>@@ -333,7 +350,7 @@ static void colo_process_checkpoint(MigrationState *s)
> >>
> >>  out:
> >>      current_time = error_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
> >>-    if (ret < 0) {
> >>+    if (ret < 0 || (!ret && !failover_request_is_active())) {
> >
> >Why is this needed - when would you get a 0 return that is actually an error?
> >
> 
> If we shutdown the fd, it will return 0, and the ret will be 0, this only happen
> when we do failover actively.

OK

> >>          error_report("%s: %s", __func__, strerror(-ret));
> >>          qapi_event_send_colo_exit(COLO_MODE_PRIMARY, COLO_EXIT_REASON_ERROR,
> >>                                    true, strerror(-ret), NULL);
> >>@@ -362,6 +379,11 @@ out:
> >>      qsb_free(buffer);
> >>      buffer = NULL;
> >>
> >>+    /* Hope this not to be too long to loop here */
> >>+    while (failover_get_state() != FAILOVER_STATUS_COMPLETED) {
> >>+        ;
> >>+    }
> >>+    /* Must be called after failover BH is completed */
> >
> >Is this the right patch for this?
> >
> 
> Yes, we must ensure the close() called after the shutdown() in failover,
> or there maybe an shutdown wrong 'fd' error, the 'fd' maybe just re-used by
> other thread after we close here, but before shutdown() in failover. This
> is a race case, which is rarely happening. I'll add more comments here.

Thanks, that makes sense; closing the wrong fd can be really hard to debug :-)

Dave

> 
> Thanks,
> Hailiang
> 
> 
> >>      if (s->rp_state.from_dst_file) {
> >>          qemu_fclose(s->rp_state.from_dst_file);
> >>      }
> >>@@ -534,7 +556,7 @@ void *colo_process_incoming_thread(void *opaque)
> >>
> >>  out:
> >>      current_time = error_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
> >>-    if (ret < 0) {
> >>+    if (ret < 0 || (!ret && !failover_request_is_active())) {
> >>          error_report("colo incoming thread will exit, detect error: %s",
> >>                       strerror(-ret));
> >>          qapi_event_send_colo_exit(COLO_MODE_SECONDARY, COLO_EXIT_REASON_ERROR,
> >>@@ -573,6 +595,11 @@ out:
> >>      */
> >>      colo_release_ram_cache();
> >>
> >>+    /* Hope this not to be too long to loop here */
> >>+    while (failover_get_state() != FAILOVER_STATUS_COMPLETED) {
> >>+        ;
> >>+    }
> >>+    /* Must be called after failover BH is completed */
> >>      if (mis->to_src_file) {
> >>          qemu_fclose(mis->to_src_file);
> >>      }
> >>--
> >>1.8.3.1
> >>
> >>
> >--
> >Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> >
> >.
> >
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK