[src/trunk]: src/sys/miscfs/genfs Protect genfs_getpages() against vnodes dis...

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

details:   https://anonhg.NetBSD.org/src/rev/03b2e3fd6688
branches:  trunk
changeset: 351853:03b2e3fd6688
user:      hannken <hannken%NetBSD.org@localhost>
date:      Wed Mar 01 10:47:26 2017 +0000

description:
Protect genfs_getpages() against vnodes disappearing during a
forced mount update from read-write to read-only.

diffstat:

 sys/miscfs/genfs/genfs_io.c |  39 +++++++++++++++++++++++----------------
 1 files changed, 23 insertions(+), 16 deletions(-)

diffs (80 lines):

diff -r f02e2b3d0ca1 -r 03b2e3fd6688 sys/miscfs/genfs/genfs_io.c
--- a/sys/miscfs/genfs/genfs_io.c       Wed Mar 01 10:46:43 2017 +0000
+++ b/sys/miscfs/genfs/genfs_io.c       Wed Mar 01 10:47:26 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: genfs_io.c,v 1.63 2016/09/29 19:08:48 christos Exp $   */
+/*     $NetBSD: genfs_io.c,v 1.64 2017/03/01 10:47:26 hannken Exp $    */
 
 /*
  * Copyright (c) 1982, 1986, 1989, 1993
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: genfs_io.c,v 1.63 2016/09/29 19:08:48 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: genfs_io.c,v 1.64 2017/03/01 10:47:26 hannken Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -129,8 +129,8 @@
        const bool overwrite = (flags & PGO_OVERWRITE) != 0;
        const bool blockalloc = memwrite && (flags & PGO_NOBLOCKALLOC) == 0;
        const bool glocked = (flags & PGO_GLOCKHELD) != 0;
-       const bool need_wapbl = blockalloc && vp->v_mount->mnt_wapbl;
-       bool has_trans_wapbl = false;
+       bool holds_wapbl = false;
+       struct mount *trans_mount = NULL;
        UVMHIST_FUNC("genfs_getpages"); UVMHIST_CALLED(ubchist);
 
        UVMHIST_LOG(ubchist, "vp %p off 0x%x/%x count %d",
@@ -291,20 +291,27 @@
        UVMHIST_LOG(ubchist, "ridx %d npages %d startoff %ld endoff %ld",
            ridx, npages, startoffset, endoffset);
 
-       if (!has_trans_wapbl) {
-               fstrans_start(vp->v_mount, FSTRANS_SHARED);
+       if (trans_mount == NULL) {
+               trans_mount = vp->v_mount;
+               fstrans_start(trans_mount, FSTRANS_SHARED);
+               /*
+                * check if this vnode is still valid.
+                */
+               mutex_enter(vp->v_interlock);
+               error = vdead_check(vp, 0);
+               mutex_exit(vp->v_interlock);
+               if (error)
+                       goto out_err_free;
                /*
                 * XXX: This assumes that we come here only via
                 * the mmio path
                 */
-               if (need_wapbl) {
-                       error = WAPBL_BEGIN(vp->v_mount);
-                       if (error) {
-                               fstrans_done(vp->v_mount);
+               if (blockalloc && vp->v_mount->mnt_wapbl) {
+                       error = WAPBL_BEGIN(trans_mount);
+                       if (error)
                                goto out_err_free;
-                       }
+                       holds_wapbl = true;
                }
-               has_trans_wapbl = true;
        }
 
        /*
@@ -491,10 +498,10 @@
        if (pgs != NULL && pgs != pgs_onstack)
                kmem_free(pgs, pgs_size);
 out_err:
-       if (has_trans_wapbl) {
-               if (need_wapbl)
-                       WAPBL_END(vp->v_mount);
-               fstrans_done(vp->v_mount);
+       if (trans_mount != NULL) {
+               if (holds_wapbl)
+                       WAPBL_END(trans_mount);
+               fstrans_done(trans_mount);
        }
        return error;
 }