PERFORCE change 83531 for review

[Robert Watson]

http://perforce.freebsd.org/chv.cgi?CH=83531

Change 83531 by rwatson at rwatson_zoo on 2005/09/13 09:48:42

	Revert if->while change, the comments were right: we don't want
	to guarantee the condition is the case, just that it has been
	the case.

Affected files ...

.. //depot/projects/netsmp/src/sys/fs/fifofs/fifo_vnops.c#10 edit

Differences ...

==== //depot/projects/netsmp/src/sys/fs/fifofs/fifo_vnops.c#10 (text+ko) ====

@@ -176,12 +176,6 @@
 	struct file *fp;
 	int error;
 
-	/*
-	 * In theory, writes to vp->v_fifoinfo are serialized by the vnode
-	 * lock, so there can't be a race between multiple simultaneous opens
-	 * here.  We assert there hasn't been at the end of the allocation,
-	 * however, to be sure.
-	 */
 	if ((fip = vp->v_fifoinfo) == NULL) {
 		MALLOC(fip, struct fifoinfo *, sizeof(*fip), M_VNODE, M_WAITOK);
 		error = socreate(AF_LOCAL, &rso, SOCK_STREAM, 0, cred, td);
@@ -206,10 +200,6 @@
 		SOCKBUF_LOCK(&rso->so_rcv);
 		rso->so_rcv.sb_state |= SBS_CANTRCVMORE;
 		SOCKBUF_UNLOCK(&rso->so_rcv);
-		/*
-		 * If the vnode lock is insufficiently serializing, we might
-		 * have to detect a race here and recover.
-		 */
 		KASSERT(vp->v_fifoinfo == NULL,
 		    ("fifo_open: v_fifoinfo race"));
 		vp->v_fifoinfo = fip;
@@ -255,7 +245,7 @@
 		}
 	}
 	if ((ap->a_mode & O_NONBLOCK) == 0) {
-		while ((ap->a_mode & FREAD) && fip->fi_writers == 0) {
+		if ((ap->a_mode & FREAD) && fip->fi_writers == 0) {
 			VOP_UNLOCK(vp, 0, td);
 			error = msleep(&fip->fi_readers, &fifo_mtx,
 			    PDROP | PCATCH | PSOCK, "fifoor", 0);
@@ -269,8 +259,13 @@
 				return (error);
 			}
 			mtx_lock(&fifo_mtx);
+			/*
+			 * We must have got woken up because we had a writer.
+			 * That (and not still having one) is the condition
+			 * that we must wait for.
+			 */
 		}
-		while ((ap->a_mode & FWRITE) && fip->fi_readers == 0) {
+		if ((ap->a_mode & FWRITE) && fip->fi_readers == 0) {
 			VOP_UNLOCK(vp, 0, td);
 			error = msleep(&fip->fi_writers, &fifo_mtx,
 			    PDROP | PCATCH | PSOCK, "fifoow", 0);
@@ -283,6 +278,11 @@
 				}
 				return (error);
 			}
+			/*
+			 * We must have got woken up because we had
+			 * a reader.  That (and not still having one)
+			 * is the condition that we must wait for.
+			 */
 			mtx_lock(&fifo_mtx);
 		}
 	}