performance/write-behind: do __wb_request_unref within locks

Since __wb_request_unref can remove the request from various lists,
calling it without holding wb_inode->lock results in corruptions when
other threads simultaneously try to access the lists this request is
part of.

Thanks to "Nithya Balachandran" <nbalacha@redhat.com> for pointing out
the bug.

Change-Id: I78fb6433c2e212500d07780f7b45c5a0e2bf9209
Signed-off-by: Raghavendra G <rgowdapp@redhat.com>
Reviewed-on: https://review.gluster.org/16464
Smoke: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/xlators/performance/write-behind/src/write-behind.c b/xlators/performance/write-behind/src/write-behind.c
index cf8dd1f9e00..877d9217f5d 100644
--- a/xlators/performance/write-behind/src/write-behind.c
+++ b/xlators/performance/write-behind/src/write-behind.c
@@ -1021,12 +1021,11 @@ wb_fulfill_short_write (wb_request_t *head, int size)
                         }
 
                 }
-        }
 done:
+                __wb_request_unref (head);
+        }
         UNLOCK (&wb_inode->lock);
 
-        __wb_request_unref (head);
-
         wb_add_head_for_retry (req);
 out:
         return;