[src/trunk]: src/sys/kern brelsel: Clear B_COWDONE flag on clean (! BO_DELWRI...

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

details:   https://anonhg.NetBSD.org/src/rev/4f162bbc2173
branches:  trunk
changeset: 759526:4f162bbc2173
user:      hannken <hannken%NetBSD.org@localhost>
date:      Sun Dec 12 10:30:09 2010 +0000

description:
brelsel: Clear B_COWDONE flag on clean (! BO_DELWRI) buffer.  B_COWDONE is set
if the buffer was read with intention to modify but the caller changed its mind.

This error could lead to snapshot corruption when a buffer with B_COWDONE set
resides on the freelist and we create a new snapshot.

diffstat:

 sys/kern/vfs_bio.c |  12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diffs (33 lines):

diff -r d9333e76a737 -r 4f162bbc2173 sys/kern/vfs_bio.c
--- a/sys/kern/vfs_bio.c        Sun Dec 12 10:29:25 2010 +0000
+++ b/sys/kern/vfs_bio.c        Sun Dec 12 10:30:09 2010 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_bio.c,v 1.224 2010/11/02 15:09:52 pooka Exp $      */
+/*     $NetBSD: vfs_bio.c,v 1.225 2010/12/12 10:30:09 hannken Exp $    */
 
 /*-
  * Copyright (c) 2007, 2008, 2009 The NetBSD Foundation, Inc.
@@ -123,7 +123,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.224 2010/11/02 15:09:52 pooka Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.225 2010/12/12 10:30:09 hannken Exp $");
 
 #include "opt_bufcache.h"
 
@@ -983,6 +983,14 @@
        if (ISSET(bp->b_cflags, BC_WANTED))
                CLR(bp->b_cflags, BC_WANTED|BC_AGE);
 
+       /* If it's clean clear the copy-on-write flag. */
+       if (ISSET(bp->b_flags, B_COWDONE)) {
+               mutex_enter(bp->b_objlock);
+               if (!ISSET(bp->b_oflags, BO_DELWRI))
+                       CLR(bp->b_flags, B_COWDONE);
+               mutex_exit(bp->b_objlock);
+       }
+
        /*
         * Determine which queue the buffer should be on, then put it there.
         */