From 3ee3fef23ff91d6bf974820b4dbe8280c6ad27b2 Mon Sep 17 00:00:00 2001

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Date: Fri, 22 Jun 2018 19:00:04 +0200

Subject: [PATCH 16/21] migration: not wait RDMA_CM_EVENT_DISCONNECTED event

 after rdma_disconnect

RH-Author: Dr. David Alan Gilbert <dgilbert@redhat.com>

Message-id: <20180801135522.11658-18-dgilbert@redhat.com>

Patchwork-id: 81572

O-Subject: [qemu-kvm RHEL8/virt212 PATCH 17/18] migration: not wait RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect

Bugzilla: 1594384

RH-Acked-by: Peter Xu <peterx@redhat.com>

RH-Acked-by: John Snow <jsnow@redhat.com>

RH-Acked-by: Juan Quintela <quintela@redhat.com>

From: Lidong Chen <jemmy858585@gmail.com>

When cancel migration during RDMA precopy, the source qemu main thread hangs sometime.

The backtrace is:

    (gdb) bt

    #0  0x00007f249eabd43d in write () from /lib64/libpthread.so.0

    #1  0x00007f24a1ce98e4 in rdma_get_cm_event (channel=0x4675d10, event=0x7ffe2f643dd0) at src/cma.c:2189

    #2  0x00000000007b6166 in qemu_rdma_cleanup (rdma=0x6784000) at migration/rdma.c:2296

    #3  0x00000000007b7cae in qio_channel_rdma_close (ioc=0x3bfcc30, errp=0x0) at migration/rdma.c:2999

    #4  0x00000000008db60e in qio_channel_close (ioc=0x3bfcc30, errp=0x0) at io/channel.c:273

    #5  0x00000000007a8765 in channel_close (opaque=0x3bfcc30) at migration/qemu-file-channel.c:98

    #6  0x00000000007a71f9 in qemu_fclose (f=0x527c000) at migration/qemu-file.c:334

    #7  0x0000000000795b96 in migrate_fd_cleanup (opaque=0x3b46280) at migration/migration.c:1162

    #8  0x000000000093a71b in aio_bh_call (bh=0x3db7a20) at util/async.c:90

    #9  0x000000000093a7b2 in aio_bh_poll (ctx=0x3b121c0) at util/async.c:118

    #10 0x000000000093f2ad in aio_dispatch (ctx=0x3b121c0) at util/aio-posix.c:436

    #11 0x000000000093ab41 in aio_ctx_dispatch (source=0x3b121c0, callback=0x0, user_data=0x0)

        at util/async.c:261

    #12 0x00007f249f73c7aa in g_main_context_dispatch () from /lib64/libglib-2.0.so.0

    #13 0x000000000093dc5e in glib_pollfds_poll () at util/main-loop.c:215

    #14 0x000000000093dd4e in os_host_main_loop_wait (timeout=28000000) at util/main-loop.c:263

    #15 0x000000000093de05 in main_loop_wait (nonblocking=0) at util/main-loop.c:522

    #16 0x00000000005bc6a5 in main_loop () at vl.c:1944

    #17 0x00000000005c39b5 in main (argc=56, argv=0x7ffe2f6443f8, envp=0x3ad0030) at vl.c:4752

It does not get the RDMA_CM_EVENT_DISCONNECTED event after rdma_disconnect sometime.

According to IB Spec once active side send DREQ message, it should wait for DREP message

and only once it arrived it should trigger a DISCONNECT event. DREP message can be dropped

due to network issues.

For that case the spec defines a DREP_timeout state in the CM state machine, if the DREP is

dropped we should get a timeout and a TIMEWAIT_EXIT event will be trigger.

Unfortunately the current kernel CM implementation doesn't include the DREP_timeout state

and in above scenario we will not get DISCONNECT or TIMEWAIT_EXIT events.

So it should not invoke rdma_get_cm_event which may hang forever, and the event channel

is also destroyed in qemu_rdma_cleanup.

Signed-off-by: Lidong Chen <lidongchen@tencent.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Signed-off-by: Juan Quintela <quintela@redhat.com>

(cherry picked from commit c5e76115ccb4979cec795a8ae38becd07c2fde9f)

---

 migration/rdma.c       | 12 ++----------

 migration/trace-events |  1 -

 2 files changed, 2 insertions(+), 11 deletions(-)

diff --git a/migration/rdma.c b/migration/rdma.c

index 7d233b0..6e29ebf 100644

--- a/migration/rdma.c

+++ b/migration/rdma.c

@@ -2268,8 +2268,7 @@ static int qemu_rdma_write(QEMUFile *f, RDMAContext *rdma,

 static void qemu_rdma_cleanup(RDMAContext *rdma)

 {

-    struct rdma_cm_event *cm_event;

-    int ret, idx;

+    int idx;

     if (rdma->cm_id && rdma->connected) {

         if ((rdma->error_state ||

@@ -2283,14 +2282,7 @@ static void qemu_rdma_cleanup(RDMAContext *rdma)

             qemu_rdma_post_send_control(rdma, NULL, &head;;

         }

-        ret = rdma_disconnect(rdma->cm_id);

-        if (!ret) {

-            trace_qemu_rdma_cleanup_waiting_for_disconnect();

-            ret = rdma_get_cm_event(rdma->channel, &cm_event);

-            if (!ret) {

-                rdma_ack_cm_event(cm_event);

-            }

-        }

+        rdma_disconnect(rdma->cm_id);

         trace_qemu_rdma_cleanup_disconnect();

         rdma->connected = false;

     }

diff --git a/migration/trace-events b/migration/trace-events

index a180d7b..92b3179 100644

--- a/migration/trace-events

+++ b/migration/trace-events

@@ -123,7 +123,6 @@ qemu_rdma_accept_pin_state(bool pin) "%d"

 qemu_rdma_accept_pin_verbsc(void *verbs) "Verbs context after listen: %p"

 qemu_rdma_block_for_wrid_miss(const char *wcompstr, int wcomp, const char *gcompstr, uint64_t req) "A Wanted wrid %s (%d) but got %s (%" PRIu64 ")"

 qemu_rdma_cleanup_disconnect(void) ""

-qemu_rdma_cleanup_waiting_for_disconnect(void) ""

 qemu_rdma_close(void) ""

 qemu_rdma_connect_pin_all_requested(void) ""

 qemu_rdma_connect_pin_all_outcome(bool pin) "%d"

-- 

1.8.3.1