From: Jason Dillaman <dillaman@redhat.com>
Date: Thu, 7 May 2015 16:35:36 +0000 (-0400)
Subject: librbd: don't hold owner_lock for write during flush
X-Git-Tag: v9.0.2~15^2~7
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=2b6d0633d5c89de3a557cdd72621dfc19f0540de;p=ceph.git

librbd: don't hold owner_lock for write during flush

The various IO callback codepaths will attempt to take
the lock, which will result in deadlock since the flush
cannot complete.

Backport: hammer
Fixes: #11537
Signed-off-by: Jason Dillaman <dillaman@redhat.com>

Conflicts:
	src/librbd/ImageWatcher.cc
---

diff --git a/src/librbd/ImageWatcher.cc b/src/librbd/ImageWatcher.cc
index a8a7c2114d8..82e45db1693 100644
--- a/src/librbd/ImageWatcher.cc
+++ b/src/librbd/ImageWatcher.cc
@@ -376,21 +376,21 @@ bool ImageWatcher::release_lock()
     return false;
   }
   prepare_unlock();
-
   m_image_ctx.owner_lock.put_write();
   m_image_ctx.cancel_async_requests();
   m_image_ctx.flush_async_operations();
-  m_image_ctx.owner_lock.get_write();
-
-  if (!is_lock_owner()) {
-    return false;
-  }
 
   {
-    RWLock::WLocker l2(m_image_ctx.md_lock);
+    RWLock::RLocker owner_locker(m_image_ctx.owner_lock);
+    RWLock::WLocker md_locker(m_image_ctx.md_lock);
     librbd::_flush(&m_image_ctx);
   }
 
+  m_image_ctx.owner_lock.get_write();
+  if (!is_lock_owner()) {
+    return false;
+  }
+
   unlock();
   return true;
 }