From 0b8644b0cd35479fe1c2f51ccb5e0e494e4c7f91 Mon Sep 17 00:00:00 2001
From: Sage Weil <sage@redhat.com>
Date: Wed, 12 Apr 2017 14:19:46 -0400
Subject: [PATCH] os/bluestore: fix narrow osr->flush() race

Signed-off-by: Sage Weil <sage@redhat.com>
---
 src/os/bluestore/BlueStore.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/os/bluestore/BlueStore.h b/src/os/bluestore/BlueStore.h
index 8c7732fa837..535c745ae53 100644
--- a/src/os/bluestore/BlueStore.h
+++ b/src/os/bluestore/BlueStore.h
@@ -1655,10 +1655,13 @@ public:
     void flush() override {
       std::unique_lock<std::mutex> l(qlock);
       while (true) {
+	// set flag before the check because the condition
+	// may become true outside qlock, and we need to make
+	// sure those threads see waiters and signal qcond.
+	++kv_submitted_waiters;
 	if (_is_all_kv_submitted()) {
 	  return;
 	}
-	++kv_submitted_waiters;
 	qcond.wait(l);
 	--kv_submitted_waiters;
       }