Author: kib
Date: Wed Jun 15 15:56:03 2016
New Revision: 301929
URL: https://svnweb.freebsd.org/changeset/base/301929
Log:
Do not assume that we own the use reference on the covered vnode until
we set MNTK_UNMOUNT flag on the mp. Otherwise parallel unmount which
wins race with us could dereference the covered vnode, and we are
left with the locked freed memory.
Reported and tested by: pho
Sponsored by: The FreeBSD Foundation
Approved by: re (gjb)
MFC after: 1 week
Modified:
head/sys/kern/vfs_mount.c
Modified: head/sys/kern/vfs_mount.c
==============================================================================
--- head/sys/kern/vfs_mount.c Wed Jun 15 15:55:14 2016 (r301928)
+++ head/sys/kern/vfs_mount.c Wed Jun 15 15:56:03 2016 (r301929)
@@ -1220,7 +1220,6 @@ dounmount(struct mount *mp, int flags, s
VI_LOCK(coveredvp);
vholdl(coveredvp);
vn_lock(coveredvp, LK_EXCLUSIVE | LK_INTERLOCK | LK_RETRY);
- vdrop(coveredvp);
/*
* Check for mp being unmounted while waiting for the
* covered vnode lock.
@@ -1228,18 +1227,22 @@ dounmount(struct mount *mp, int flags, s
if (coveredvp->v_mountedhere != mp ||
coveredvp->v_mountedhere->mnt_gen != mnt_gen_r) {
VOP_UNLOCK(coveredvp, 0);
+ vdrop(coveredvp);
vfs_rel(mp);
return (EBUSY);
}
}
+
/*
* Only privileged root, or (if MNT_USER is set) the user that did the
* original mount is permitted to unmount this filesystem.
*/
error = vfs_suser(mp, td);
if (error != 0) {
- if (coveredvp)
+ if (coveredvp != NULL) {
VOP_UNLOCK(coveredvp, 0);
+ vdrop(coveredvp);
+ }
vfs_rel(mp);
return (error);
}
@@ -1249,8 +1252,10 @@ dounmount(struct mount *mp, int flags, s
if ((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0 ||
!TAILQ_EMPTY(&mp->mnt_uppers)) {
MNT_IUNLOCK(mp);
- if (coveredvp)
+ if (coveredvp != NULL) {
VOP_UNLOCK(coveredvp, 0);
+ vdrop(coveredvp);
+ }
vn_finished_write(mp);
return (EBUSY);
}
@@ -1283,6 +1288,16 @@ dounmount(struct mount *mp, int flags, s
if (mp->mnt_flag & MNT_EXPUBLIC)
vfs_setpublicfs(NULL, NULL, NULL);
+ /*
+ * From now, we can claim that the use reference on the
+ * coveredvp is ours, and the ref can be released only by
+ * successfull unmount by us, or left for later unmount
+ * attempt. The previously acquired hold reference is no
+ * longer needed to protect the vnode from reuse.
+ */
+ if (coveredvp != NULL)
+ vdrop(coveredvp);
+
vfs_msync(mp, MNT_WAIT);
MNT_ILOCK(mp);
async_flag = mp->mnt_flag & MNT_ASYNC;
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