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- We can not hold a vnode lock while we do a lookup. Search for and load

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modules prior to looking up the directory which we will cover to avoid
   this problem in mount.
 - We must hold the coveredvp locked before we can busy the mountpoint to
   prevent a lock order reversal with the vfs_busy() in lookup which holds
   the directory lock prior to doing a vfs_busy().  The directory lock is
   required to safely clear the v_mountedhere field on the directory.

MFC After:	1 week
This commit is contained in:
Jeff Roberson 2006-02-22 06:29:55 +00:00
parent 8a7cd2fdfb
commit a4aeaefe5a
1 changed files with 25 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

44
sys/kern/vfs_mount.c
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@ -466,6 +466,7 @@ vfs_mount_destroy(struct mount *mp, struct thread *td)
{
int i;
vfs_unbusy(mp, td);
MNT_ILOCK(mp);
for (i = 0; mp->mnt_ref && i < 3; i++)
msleep(mp, MNT_MTX(mp), PVFS, "mntref", hz);
@ -501,7 +502,6 @@ vfs_mount_destroy(struct mount *mp, struct thread *td)
mp->mnt_vfc->vfc_refcount--;
if (!TAILQ_EMPTY(&mp->mnt_nvnodelist))
panic("unmount: dangling vnode");
vfs_unbusy(mp,td);
lockdestroy(&mp->mnt_lock);
MNT_ILOCK(mp);
if (mp->mnt_kern_flag & MNTK_MWAIT)
@ -741,7 +741,6 @@ vfs_domount(
struct nameidata nd;
mtx_assert(&Giant, MA_OWNED);
/*
* Be ultra-paranoid about making sure the type and fspath
* variables will fit in our mp buffers, including the
@ -770,6 +769,18 @@ vfs_domount(
*/
if (suser(td) != 0)
fsflags |= MNT_NOSUID | MNT_USER;
/* Load KLDs before we lock the covered vnode to avoid reversals. */
vfsp = NULL;
if ((fsflags & MNT_UPDATE) == 0) {
/* Don't try to load KLDs if we're mounting the root. */
if (fsflags & MNT_ROOTFS)
vfsp = vfs_byname(fstype);
else
vfsp = vfs_byname_kld(fstype, td, &error);
if (vfsp == NULL)
return (ENODEV);
}
/*
* Get vnode to be covered
*/
@ -848,19 +859,6 @@ vfs_domount(
vput(vp);
return (ENOTDIR);
}
/* Don't try to load KLDs if we're mounting the root. */
if (fsflags & MNT_ROOTFS) {
if ((vfsp = vfs_byname(fstype)) == NULL) {
vput(vp);
return (ENODEV);
}
} else {
vfsp = vfs_byname_kld(fstype, td, &error);
if (vfsp == NULL) {
vput(vp);
return (error);
}
}
VI_LOCK(vp);
if ((vp->v_iflag & VI_MOUNT) != 0 ||
vp->v_mountedhere != NULL) {
@ -1069,9 +1067,13 @@ dounmount(mp, flags, td)
mtx_assert(&Giant, MA_OWNED);
if ((coveredvp = mp->mnt_vnodecovered) != NULL)
vn_lock(coveredvp, LK_EXCLUSIVE | LK_RETRY, td);
MNT_ILOCK(mp);
if (mp->mnt_kern_flag & MNTK_UNMOUNT) {
MNT_IUNLOCK(mp);
if (coveredvp)
VOP_UNLOCK(coveredvp, 0, td);
return (EBUSY);
}
mp->mnt_kern_flag |= MNTK_UNMOUNT;
@ -1086,6 +1088,8 @@ dounmount(mp, flags, td)
if (mp->mnt_kern_flag & MNTK_MWAIT)
wakeup(mp);
MNT_IUNLOCK(mp);
if (coveredvp)
VOP_UNLOCK(coveredvp, 0, td);
return (error);
}
vn_start_write(NULL, &mp, V_WAIT);
@ -1141,17 +1145,19 @@ dounmount(mp, flags, td)
if (mp->mnt_kern_flag & MNTK_MWAIT)
wakeup(mp);
MNT_IUNLOCK(mp);
if (coveredvp)
VOP_UNLOCK(coveredvp, 0, td);
return (error);
}
mtx_lock(&mountlist_mtx);
TAILQ_REMOVE(&mountlist, mp, mnt_list);
if ((coveredvp = mp->mnt_vnodecovered) != NULL)
coveredvp->v_mountedhere = NULL;
mtx_unlock(&mountlist_mtx);
if (coveredvp != NULL) {
coveredvp->v_mountedhere = NULL;
vput(coveredvp);
}
vfs_event_signal(NULL, VQ_UNMOUNT, 0);
vfs_mount_destroy(mp, td);
if (coveredvp != NULL)
vrele(coveredvp);
return (0);
}