librados: fix locking for AioCompletionImpl refcounting

Add an already-locked helper so that C_Aio{Safe,Complete} can
increment the reference count when their caller holds the
lock. C_AioCompleteAndSafe's caller is not holding the lock, so call
regular get() to ensure no racing updates can occur.

This eliminates all direct manipulations of AioCompletionImpl->ref,
and makes the necessary locking clear.

The only place C_AioCompleteAndSafe is used is in handling
aio_flush_async(). This could cause a missing completion.

Refs: #5919
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
Tested-by: Oliver Francke <Oliver.Francke@filoo.de>

1 files changed, 9 insertions, 5 deletions

diff --git a/src/librados/AioCompletionImpl.h b/src/librados/AioCompletionImpl.h
index 34462d22063..cf049e0a9a2 100644
--- a/src/librados/AioCompletionImpl.h
+++ b/src/librados/AioCompletionImpl.h
@@ -134,10 +134,14 @@ struct librados::AioCompletionImpl {
 
   void get() {
     lock.Lock();
-    assert(ref > 0);
-    ref++;
+    _get();
     lock.Unlock();
   }
+  void _get() {
+    assert(lock.is_locked());
+    assert(ref > 0);
+    ++ref;
+  }
   void release() {
     lock.Lock();
     assert(!released);
@@ -162,7 +166,7 @@ struct C_AioComplete : public Context {
   AioCompletionImpl *c;
 
   C_AioComplete(AioCompletionImpl *cc) : c(cc) {
-    c->ref++;
+    c->_get();
   }
 
   void finish(int r) {
@@ -181,7 +185,7 @@ struct C_AioSafe : public Context {
   AioCompletionImpl *c;
 
   C_AioSafe(AioCompletionImpl *cc) : c(cc) {
-    c->ref++;
+    c->_get();
   }
 
   void finish(int r) {
@@ -208,7 +212,7 @@ struct C_AioCompleteAndSafe : public Context {
   AioCompletionImpl *c;
 
   C_AioCompleteAndSafe(AioCompletionImpl *cc) : c(cc) {
-    c->ref++;
+    c->get();
   }
 
   void finish(int r) {