b_waiters cannot be adequately protected by the interlock because it is

dropped after the call to lockmgr() so just revert this approach using
something similar to the precedent one:
BUF_LOCKWAITERS() just checks if there are waiters (not the actual number
of them) and it is based on newly introduced lockmgr_waiters() which
returns if the lockmgr has waiters or not. The name has been choosen
differently by old lockwaiters() in order to not confuse them.

KPI results enriched by this commit so __FreeBSD_version bumping and
manpage update will be happening soon.
'struct buf' also changes, so kernel ABI is disturbed.

Bug found by:	jeff
Approved by:	jeff, kib

1 files changed, 1 insertions, 5 deletions

diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index b3bd6f6..84de803 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -1527,12 +1527,11 @@ bgetvp(struct vnode *vp, struct buf *bp)
 /*
  * Disassociate a buffer from a vnode.
  */
-int
+void
 brelvp(struct buf *bp)
 {
 	struct bufobj *bo;
 	struct vnode *vp;
-	int waiters;
 
 	CTR3(KTR_BUF, "brelvp(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
 	KASSERT(bp->b_vp != NULL, ("brelvp: NULL"));
@@ -1557,11 +1556,8 @@ brelvp(struct buf *bp)
 	bp->b_flags &= ~B_NEEDSGIANT;
 	bp->b_vp = NULL;
 	bp->b_bufobj = NULL;
-	waiters = bp->b_waiters;
 	BO_UNLOCK(bo);
 	vdrop(vp);
-
-	return (waiters);
 }
 
 /*