From 6fbdb2adf57e58f16742a35758d74a11fc419e6f Mon Sep 17 00:00:00 2001
From: gdt <gdt@NetBSD.org>
Date: Thu, 12 Jan 2006 14:57:06 +0000
Subject: [PATCH] In coda_lookup, add LK_RETRY to locking of child vnode.  The
 previous code paniced if the first attempt to lock the vnode failed, and such
 failures are not errors - just cause to wait.  gdt was regularly hitting this
 panic.

Correct one of two identical panic messages.

Add XXX comments about

  ISDOTDOT locking rules not being followed

  questioning the practice of unlocking parent before locking child.
  (But, given that the vnode is referenced, it can't be deleted, so
  maybe this is fine.)

  Why is failured to unlock not a panic but failure to lock is?
---
 sys/coda/coda_vnops.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/sys/coda/coda_vnops.c b/sys/coda/coda_vnops.c
index 21755c35a415..19137c9f0a89 100644
--- a/sys/coda/coda_vnops.c
+++ b/sys/coda/coda_vnops.c
@@ -6,7 +6,7 @@ mkdir
 rmdir
 symlink
 */
-/*	$NetBSD: coda_vnops.c,v 1.45 2005/12/11 12:19:50 christos Exp $	*/
+/*	$NetBSD: coda_vnops.c,v 1.46 2006/01/12 14:57:06 gdt Exp $	*/
 
 /*
  *
@@ -54,7 +54,7 @@ symlink
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: coda_vnops.c,v 1.45 2005/12/11 12:19:50 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: coda_vnops.c,v 1.46 2006/01/12 14:57:06 gdt Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -1006,7 +1006,12 @@ coda_lookup(void *v)
      * we are ISLASTCN
      */
     if (!error || (error == EJUSTRETURN)) {
+	/* XXX ISDOTDOT changes locking rules - not handled. */
 	if (!(cnp->cn_flags & LOCKPARENT) || !(cnp->cn_flags & ISLASTCN)) {
+	    /*
+	     * XXX Lock child before unlocking parent?
+	     * XXX Why is it ok to fail to unlock, but a panic to fail to lock?
+	     */
 	    if ((error = VOP_UNLOCK(dvp, 0))) {
 		return error;
 	    }
@@ -1016,8 +1021,7 @@ coda_lookup(void *v)
 	     * lock it without bothering to check anything else.
 	     */
 	    if (*ap->a_vpp) {
-		if ((error = vn_lock(*ap->a_vpp, LK_EXCLUSIVE))) {
-		    printf("coda_lookup: ");
+		if ((error = vn_lock(*ap->a_vpp, LK_EXCLUSIVE|LK_RETRY))) {
 		    panic("unlocked parent but couldn't lock child");
 		}
 	    }
@@ -1025,9 +1029,8 @@ coda_lookup(void *v)
 	    /* The parent is locked, and may be the same as the child */
 	    if (*ap->a_vpp && (*ap->a_vpp != dvp)) {
 		/* Different, go ahead and lock it. */
-		if ((error = vn_lock(*ap->a_vpp, LK_EXCLUSIVE))) {
-		    printf("coda_lookup: ");
-		    panic("unlocked parent but couldn't lock child");
+		if ((error = vn_lock(*ap->a_vpp, LK_EXCLUSIVE|LK_RETRY))) {
+		    panic("kept parent locked but couldn't lock child");
 		}
 	    }
 	}