librbd: avoid recursive locking of AioCompletion::lock

The caller of the callback is holding the completion lock; do not retake
it.

Fixes assert triggered when lockdep is enabled.

Signed-off-by: Sage Weil <sage@inktank.com>

2 files changed, 13 insertions, 2 deletions

diff --git a/src/librbd/AioCompletion.h b/src/librbd/AioCompletion.h
index 899586d51a7..b09ed9f9a9b 100644
--- a/src/librbd/AioCompletion.h
+++ b/src/librbd/AioCompletion.h
@@ -139,6 +139,10 @@ namespace librbd {
       lock.Unlock();
       return r;
     }
+    ssize_t _get_return_value() {
+      assert(lock.is_locked());
+      return rval;
+    }
 
     void get() {
       lock.Lock();
@@ -152,6 +156,13 @@ namespace librbd {
       released = true;
       put_unlock();
     }
+    void _release() {
+      assert(lock.is_locked());
+      assert(!released);
+      released = true;
+      int n = --ref;
+      assert(n > 0);
+    }
     void put() {
       lock.Lock();
       put_unlock();
diff --git a/src/librbd/internal.cc b/src/librbd/internal.cc
index 1fd7942f3b8..db7d55d82ff 100644
--- a/src/librbd/internal.cc
+++ b/src/librbd/internal.cc
@@ -2317,8 +2317,8 @@ reprotect_and_return_err:
   {
     Context *ctx = reinterpret_cast<Context *>(arg);
     AioCompletion *comp = reinterpret_cast<AioCompletion *>(cb);
-    ctx->complete(comp->get_return_value());
-    comp->release();
+    ctx->complete(comp->_get_return_value());  // caller already holds aioc lock
+    comp->_release();
   }
 
   int64_t read_iterate(ImageCtx *ictx, uint64_t off, uint64_t len,