From: Jianpeng Ma <jianpeng.ma@intel.com>
Date: Mon, 24 Jun 2019 12:24:36 +0000 (+0800)
Subject: msg/async: add comments for commit 294c41f18adada6ab.
X-Git-Tag: v15.1.0~2386^2
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=0d13ef2f2013b201f09d67c86f34253fb86cd736;p=ceph.git

msg/async: add comments for commit 294c41f18adada6ab.

Consider this case:
    send-thread                                 msg-work
                                            write_event()
                                             r = write_message()
connection->write_lock.lock()
if (.. && !write_in_progress) {
  write_in_progress = true;
  add external_event
}
connection->write_lock.unlock()
                                          connection->write_lock.lock()
                                          if (r > 0)
                                            break;
                                          } while ();
                                          write_in_progress = false;

For this case, we don't add external_event and in write_event we don't
check out_q whether empty rather than break.
This make msg-work never wake up again.
Fortunately, if write_message() > 0, in AsyncConnection::_try_send will
add an EVENT_WRITEABLE to wake up msg-work. So bug can't occur.

I add comment to descript this and hope get the better method to fix
this.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
---

diff --git a/src/msg/async/ProtocolV1.cc b/src/msg/async/ProtocolV1.cc
index b410a2e6b79e..1708b0c211e6 100644
--- a/src/msg/async/ProtocolV1.cc
+++ b/src/msg/async/ProtocolV1.cc
@@ -346,8 +346,11 @@ void ProtocolV1::write_event() {
       } else if (r < 0) {
         ldout(cct, 1) << __func__ << " send msg failed" << dendl;
         break;
-      } else if (r > 0)
-        break;
+      } else if (r > 0) {
+	// Outbound message in-progress, thread will be re-awoken
+	// when the outbound socket is writeable again
+	break;
+      }
     } while (can_write == WriteStatus::CANWRITE);
     write_in_progress = false;
     connection->write_lock.unlock();
diff --git a/src/msg/async/ProtocolV2.cc b/src/msg/async/ProtocolV2.cc
index 77ab2dfd9555..5eb3cf883dad 100644
--- a/src/msg/async/ProtocolV2.cc
+++ b/src/msg/async/ProtocolV2.cc
@@ -626,8 +626,11 @@ void ProtocolV2::write_event() {
       } else if (r < 0) {
         ldout(cct, 1) << __func__ << " send msg failed" << dendl;
         break;
-      } else if (r > 0)
+      } else if (r > 0) {
+	// Outbound message in-progress, thread will be re-awoken
+	// when the outbound socket is writeable again
         break;
+      }
     } while (can_write);
     write_in_progress = false;