[src/trunk]: src/sys/fs/union When union_allocvp() finds a node being cleaned...

[hannken <hannken%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/c8f468cc7d38
branches:  trunk
changeset: 771566:c8f468cc7d38
user:      hannken <hannken%NetBSD.org@localhost>
date:      Fri Nov 25 11:19:10 2011 +0000

description:
When union_allocvp() finds a node being cleaned out and the caller holds
a lock, ignore the node and continue.  To allow the cleaning to succeed
the current threadmust make progress.
For a brief time the cache may contain more than one vnode referring to
a lower node.

Don't unlock the hash mutex if getnewvnode fails -- we don't hold it.

diffstat:

 sys/fs/union/union_subr.c |  30 ++++++++++++++++++++++++++----
 1 files changed, 26 insertions(+), 4 deletions(-)

diffs (72 lines):

diff -r b76a5b4d5d21 -r c8f468cc7d38 sys/fs/union/union_subr.c
--- a/sys/fs/union/union_subr.c Fri Nov 25 11:15:24 2011 +0000
+++ b/sys/fs/union/union_subr.c Fri Nov 25 11:19:10 2011 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: union_subr.c,v 1.54 2011/11/23 19:39:11 hannken Exp $  */
+/*     $NetBSD: union_subr.c,v 1.55 2011/11/25 11:19:10 hannken Exp $  */
 
 /*
  * Copyright (c) 1994
@@ -72,7 +72,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: union_subr.c,v 1.54 2011/11/23 19:39:11 hannken Exp $");
+__KERNEL_RCSID(0, "$NetBSD: union_subr.c,v 1.55 2011/11/25 11:19:10 hannken Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -404,6 +404,18 @@
                                lflag = LK_EXCLUSIVE;
                        vp = UNIONTOV(un);
                        mutex_enter(vp->v_interlock);
+                       /*
+                        * If this node being cleaned out and our caller
+                        * holds a lock, then ignore it and continue.  To
+                        * allow the cleaning to succeed the current thread
+                        * must make progress.  For a brief time the cache
+                        * may contain more than one vnode referring to
+                        * a lower node.
+                        */
+                       if ((vp->v_iflag & VI_XLOCK) != 0 && lflag == 0) {
+                               mutex_exit(vp->v_interlock);
+                               continue;
+                       }
                        mutex_exit(&uhash_lock);
                        if (vget(vp, lflag))
                                goto loop;
@@ -484,7 +496,7 @@
                if (lowervp)
                        vrele(lowervp);
 
-               goto out;
+               return error;
        }
 
        if (docache) {
@@ -493,6 +505,17 @@
                        if (un1->un_lowervp == lowervp &&
                            un1->un_uppervp == uppervp &&
                            UNIONTOV(un1)->v_mount == mp) {
+                               vp = UNIONTOV(un1);
+                               mutex_enter(vp->v_interlock);
+                               /*
+                                * Ignore nodes being cleaned out.
+                                * See the cache lookup above.
+                                */
+                               if ((vp->v_iflag & VI_XLOCK) != 0) {
+                                       mutex_exit(vp->v_interlock);
+                                       continue;
+                               }
+                               mutex_exit(vp->v_interlock);
                                /*
                                 * Another thread beat us, push back freshly
                                 * allocated vnode and retry.
@@ -569,7 +592,6 @@
        if (xlowervp)
                vrele(xlowervp);
 
-out:
        if (docache)
                mutex_exit(&uhash_lock);