Move the atomic() mbstat.m_drops incrementing to the MGET(HDR) and

MCLGET macros in order to avoid incrementing the drop count twice.
Otherwise, in some cases, we may increment m_drops once in m_mballoc()
for example, and increment it again in m_mballoc_wait() if the
wait fails.

2 files changed, 13 insertions, 22 deletions

diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index b5569cd..5a23f67 100644
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -245,16 +245,8 @@ m_mballoc(int nmb, int how)
 	 * Also, once we run out of map space, it will be impossible to
 	 * get any more (nothing is ever freed back to the map).
 	 */
-	if (mb_map_full || ((nmb + mbstat.m_mbufs) > nmbufs)) {
-		/* 
-		 * Needs to be atomic as we may be incrementing it
-		 * while holding another mutex, like mclfree. In other
-		 * words, m_drops is not reserved solely for mbufs,
-		 * but is also available for clusters.
-		 */ 
-		atomic_add_long(&mbstat.m_drops, 1);
+	if (mb_map_full || ((nmb + mbstat.m_mbufs) > nmbufs))
 		return (0);
-	}
 
 	mtx_unlock(&mmbfree.m_mtx);
 	p = (caddr_t)kmem_malloc(mb_map, nbytes, M_NOWAIT);
@@ -343,8 +335,7 @@ m_mballoc_wait(void)
 		atomic_add_long(&mbstat.m_wait, 1);
 		if (mmbfree.m_head != NULL)
 			MBWAKEUP(m_mballoc_wid);
-	} else
-		atomic_add_long(&mbstat.m_drops, 1);
+	}
 
 	return (p);
 }
@@ -370,10 +361,8 @@ m_clalloc(int ncl, int how)
 	 * If we've hit the mcluster number limit, stop allocating from
 	 * mb_map.
 	 */
-	if (mb_map_full || ((ncl + mbstat.m_clusters) > nmbclusters)) {
-		atomic_add_long(&mbstat.m_drops, 1);
+	if (mb_map_full || ((ncl + mbstat.m_clusters) > nmbclusters))
 		return (0);
-	}
 
 	mtx_unlock(&mclfree.m_mtx);
 	p = (caddr_t)kmem_malloc(mb_map, npg_sz,
@@ -384,10 +373,8 @@ m_clalloc(int ncl, int how)
 	 * Either the map is now full, or `how' is M_DONTWAIT and there
 	 * are no pages left.
 	 */
-	if (p == NULL) {
-		atomic_add_long(&mbstat.m_drops, 1);
+	if (p == NULL)
 		return (0);
-	}
 
 	/*
 	 * We don't let go of the mutex in order to avoid a race.
@@ -429,8 +416,7 @@ m_clalloc_wait(void)
 		atomic_add_long(&mbstat.m_wait, 1);
 		if (mclfree.m_head != NULL)
 			MBWAKEUP(m_clalloc_wid);
-	} else
-		atomic_add_long(&mbstat.m_drops, 1);
+	}
 
 	return (p);
 }
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index 8fbf7b4..2471f7c 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -377,8 +377,10 @@ struct mcntfree_lst {
 		mbtypes[_mtype]++;					\
 		mtx_unlock(&mmbfree.m_mtx);				\
 		_MGET_SETUP(_mm, _mtype);				\
-	} else								\
+	} else {							\
 		mtx_unlock(&mmbfree.m_mtx);				\
+		atomic_add_long(&mbstat.m_drops, 1);			\
+	}								\
 	(m) = _mm;							\
 } while (0)
 
@@ -404,8 +406,10 @@ struct mcntfree_lst {
 		mbtypes[_mtype]++;					\
 		mtx_unlock(&mmbfree.m_mtx);				\
 		_MGETHDR_SETUP(_mm, _mtype);				\
-	} else								\
+	} else {							\
 		mtx_unlock(&mmbfree.m_mtx);				\
+		atomic_add_long(&mbstat.m_drops, 1);			\
+	}								\
 	(m) = _mm;							\
 } while (0)
 
@@ -453,7 +457,8 @@ struct mcntfree_lst {
 			_mm->m_ext.ext_size = MCLBYTES;			\
 			_mm->m_ext.ext_type = EXT_CLUSTER;		\
 		}							\
-	}								\
+	} else								\
+		atomic_add_long(&mbstat.m_drops, 1);			\
 } while (0)
 
 #define MEXTADD(m, buf, size, free, args, flags, type) do {		\