From: Jason Dillaman <dillaman@redhat.com>
Date: Wed, 9 Mar 2016 23:00:04 +0000 (-0500)
Subject: librbd: complete cache reads on cache's dedicate thread
X-Git-Tag: v0.94.7~15^2
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=refs%2Fpull%2F8011%2Fhead;p=ceph.git

librbd: complete cache reads on cache's dedicate thread

If a snapshot is created out-of-band, the next IO will result in the
cache being flushed.  If pending writeback data performs a copy-on-write,
the read from the parent will be blocked.

Fixes: #15032

Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit f9e5ae80e3b0799b5a7e1d3f93b2d85a4baff20f)
---

diff --git a/src/librbd/AioCompletion.cc b/src/librbd/AioCompletion.cc
index 6222531bedac..efbc84945ffb 100644
--- a/src/librbd/AioCompletion.cc
+++ b/src/librbd/AioCompletion.cc
@@ -177,9 +177,10 @@ namespace librbd {
   void C_CacheRead::complete(int r) {
     if (!m_enqueued) {
       // cache_lock creates a lock ordering issue -- so re-execute this context
-      // outside the cache_lock
+      // outside the cache_lock. use the writeback handler's dedicated thread
+      // to avoid blocking a dependent operation
       m_enqueued = true;
-      m_image_ctx.op_work_queue->queue(this, r);
+      m_image_ctx.writeback_handler->queue(this, r);
       return;
     }
     Context::complete(r);
diff --git a/src/librbd/LibrbdWriteback.cc b/src/librbd/LibrbdWriteback.cc
index ac778eec5455..ee14f001dbd5 100644
--- a/src/librbd/LibrbdWriteback.cc
+++ b/src/librbd/LibrbdWriteback.cc
@@ -102,6 +102,10 @@ namespace librbd {
     delete m_finisher;
   }
 
+  void LibrbdWriteback::queue(Context *ctx, int r) {
+    m_finisher->queue(ctx, r);
+  }
+
   void LibrbdWriteback::read(const object_t& oid, uint64_t object_no,
 			     const object_locator_t& oloc,
 			     uint64_t off, uint64_t len, snapid_t snapid,
@@ -114,7 +118,7 @@ namespace librbd {
 
     {
       if (!m_ictx->object_map.object_may_exist(object_no)) {
-	m_finisher->queue(req, -ENOENT);
+	queue(req, -ENOENT);
 	return;
       }
     }
diff --git a/src/librbd/LibrbdWriteback.h b/src/librbd/LibrbdWriteback.h
index b5578ae62f5c..5b65504c83da 100644
--- a/src/librbd/LibrbdWriteback.h
+++ b/src/librbd/LibrbdWriteback.h
@@ -23,6 +23,8 @@ namespace librbd {
     LibrbdWriteback(ImageCtx *ictx, Mutex& lock);
     virtual ~LibrbdWriteback();
 
+    void queue(Context *ctx, int r);
+
     // Note that oloc, trunc_size, and trunc_seq are ignored
     virtual void read(const object_t& oid, uint64_t object_no,
 		      const object_locator_t& oloc, uint64_t off, uint64_t len,