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

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

details:   https://anonhg.NetBSD.org/src/rev/6a2eec69e08d
branches:  trunk
changeset: 822247:6a2eec69e08d
user:      hannken <hannken%NetBSD.org@localhost>
date:      Thu Mar 09 10:10:02 2017 +0000

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

diffstat:

 sys/miscfs/genfs/genfs_io.c |  72 +++++++++++++++++++++++++++-----------------
 1 files changed, 44 insertions(+), 28 deletions(-)

diffs (129 lines):

diff -r fbcec08f1bca -r 6a2eec69e08d sys/miscfs/genfs/genfs_io.c
--- a/sys/miscfs/genfs/genfs_io.c       Thu Mar 09 09:57:36 2017 +0000
+++ b/sys/miscfs/genfs/genfs_io.c       Thu Mar 09 10:10:02 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: genfs_io.c,v 1.64 2017/03/01 10:47:26 hannken Exp $    */
+/*     $NetBSD: genfs_io.c,v 1.65 2017/03/09 10:10:02 hannken Exp $    */
 
 /*
  * Copyright (c) 1982, 1986, 1989, 1993
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: genfs_io.c,v 1.64 2017/03/01 10:47:26 hannken Exp $");
+__KERNEL_RCSID(0, "$NetBSD: genfs_io.c,v 1.65 2017/03/09 10:10:02 hannken Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -842,11 +842,11 @@
        bool pagedaemon = curlwp == uvm.pagedaemon_lwp;
        struct lwp * const l = curlwp ? curlwp : &lwp0;
        struct genfs_node * const gp = VTOG(vp);
+       struct mount *trans_mp;
        int flags;
        int dirtygen;
        bool modified;
-       bool need_wapbl;
-       bool has_trans;
+       bool holds_wapbl;
        bool cleanall;
        bool onworklst;
 
@@ -859,9 +859,8 @@
        UVMHIST_LOG(ubchist, "vp %p pages %d off 0x%x len 0x%x",
            vp, uobj->uo_npages, startoff, endoff - startoff);
 
-       has_trans = false;
-       need_wapbl = (!pagedaemon && vp->v_mount && vp->v_mount->mnt_wapbl &&
-           (origflags & PGO_JOURNALLOCKED) == 0);
+       trans_mp = NULL;
+       holds_wapbl = false;
 
 retry:
        modified = false;
@@ -874,10 +873,10 @@
                        if (LIST_FIRST(&vp->v_dirtyblkhd) == NULL)
                                vn_syncer_remove_from_worklist(vp);
                }
-               if (has_trans) {
-                       if (need_wapbl)
-                               WAPBL_END(vp->v_mount);
-                       fstrans_done(vp->v_mount);
+               if (trans_mp) {
+                       if (holds_wapbl)
+                               WAPBL_END(trans_mp);
+                       fstrans_done(trans_mp);
                }
                mutex_exit(slock);
                return (0);
@@ -887,24 +886,41 @@
         * the vnode has pages, set up to process the request.
         */
 
-       if (!has_trans && (flags & PGO_CLEANIT) != 0) {
-               mutex_exit(slock);
+       if (trans_mp == NULL && (flags & PGO_CLEANIT) != 0) {
                if (pagedaemon) {
-                       error = fstrans_start_nowait(vp->v_mount, FSTRANS_LAZY);
-                       if (error)
-                               return error;
-               } else
-                       fstrans_start(vp->v_mount, FSTRANS_LAZY);
-               if (need_wapbl) {
-                       error = WAPBL_BEGIN(vp->v_mount);
+                       /* Pagedaemon must not sleep here. */
+                       trans_mp = vp->v_mount;
+                       error = fstrans_start_nowait(trans_mp, FSTRANS_LAZY);
                        if (error) {
-                               fstrans_done(vp->v_mount);
+                               mutex_exit(slock);
                                return error;
                        }
+               } else {
+                       /*
+                        * Cannot use vdeadcheck() here as this operation
+                        * usually gets used from VOP_RECLAIM().  Test for
+                        * change of v_mount instead and retry on change.
+                        */
+                       mutex_exit(slock);
+                       trans_mp = vp->v_mount;
+                       fstrans_start(trans_mp, FSTRANS_LAZY);
+                       if (vp->v_mount != trans_mp) {
+                               fstrans_done(trans_mp);
+                               trans_mp = NULL;
+                       } else {
+                               holds_wapbl = (trans_mp->mnt_wapbl &&
+                                   (origflags & PGO_JOURNALLOCKED) == 0);
+                               if (holds_wapbl) {
+                                       error = WAPBL_BEGIN(trans_mp);
+                                       if (error) {
+                                               fstrans_done(trans_mp);
+                                               return error;
+                                       }
+                               }
+                       }
+                       mutex_enter(slock);
+                       goto retry;
                }
-               has_trans = true;
-               mutex_enter(slock);
-               goto retry;
        }
 
        error = 0;
@@ -1277,10 +1293,10 @@
                goto retry;
        }
 
-       if (has_trans) {
-               if (need_wapbl)
-                       WAPBL_END(vp->v_mount);
-               fstrans_done(vp->v_mount);
+       if (trans_mp) {
+               if (holds_wapbl)
+                       WAPBL_END(trans_mp);
+               fstrans_done(trans_mp);
        }
 
        return (error);