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Fix the race between dotdot lookup and forced unmount, by using

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msdosfs-specific variant of vn_vget_ino(), msdosfs_deget_dotdot().

As was done for UFS, relookup the dotdot denode after the call to
msdosfs_deget_dotdot(), because vnode lock is dropped and directory
might be moved.

Tested by:	pho
MFC after:	3 weeks
This commit is contained in:
Konstantin Belousov 2010-02-28 17:17:29 +00:00
parent 30e65ad1bb
commit db811dd724
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=204474
1 changed files with 81 additions and 23 deletions
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104
sys/fs/msdosfs/msdosfs_lookup.c
View File

@ -61,6 +61,18 @@
#include <fs/msdosfs/fat.h>
#include <fs/msdosfs/msdosfsmount.h>
static int msdosfs_lookup_(struct vnode *vdp, struct vnode **vpp,
struct componentname *cnp, u_int64_t *inum);
static int msdosfs_deget_dotdot(struct vnode *vp, u_long cluster, int blkoff,
struct vnode **rvp);
int
msdosfs_lookup(struct vop_cachedlookup_args *ap)
{
return (msdosfs_lookup_(ap->a_dvp, ap->a_vpp, ap->a_cnp, NULL));
}
/*
* When we search a directory the blocks containing directory entries are
* read and examined. The directory entries contain information that would
@ -76,18 +88,11 @@
* out to disk. This way disk blocks containing directory entries and in
* memory denode's will be in synch.
*/
int
msdosfs_lookup(ap)
struct vop_cachedlookup_args /* {
struct vnode *a_dvp;
struct vnode **a_vpp;
struct componentname *a_cnp;
} */ *ap;
static int
msdosfs_lookup_(struct vnode *vdp, struct vnode **vpp,
struct componentname *cnp, u_int64_t *dd_inum)
{
struct mbnambuf nb;
struct vnode *vdp = ap->a_dvp;
struct vnode **vpp = ap->a_vpp;
struct componentname *cnp = ap->a_cnp;
daddr_t bn;
int error;
int slotcount;
@ -109,6 +114,7 @@ msdosfs_lookup(ap)
int flags = cnp->cn_flags;
int nameiop = cnp->cn_nameiop;
int unlen;
u_int64_t inode1;
int wincnt = 1;
int chksum = -1, chksum_ok;
@ -119,12 +125,14 @@ msdosfs_lookup(ap)
#endif
dp = VTODE(vdp);
pmp = dp->de_pmp;
*vpp = NULL;
if (vpp != NULL)
*vpp = NULL;
#ifdef MSDOSFS_DEBUG
printf("msdosfs_lookup(): vdp %p, dp %p, Attr %02x\n",
vdp, dp, dp->de_Attributes);
#endif
restart:
/*
* If they are going after the . or .. entry in the root directory,
* they won't find it. DOS filesystems don't have them in the root
@ -436,6 +444,11 @@ msdosfs_lookup(ap)
if (FAT32(pmp) && scn == MSDOSFSROOT)
scn = pmp->pm_rootdirblk;
if (dd_inum != NULL) {
*dd_inum = (uint64_t)pmp->pm_bpcluster * scn + blkoff;
return (0);
}
/*
* If deleting, and at end of pathname, return
* parameters which can be used to remove file.
@ -508,23 +521,25 @@ msdosfs_lookup(ap)
* inodes from the root, moving down the directory tree. Thus
* when following backward pointers ".." we must unlock the
* parent directory before getting the requested directory.
* There is a potential race condition here if both the current
* and parent directories are removed before the VFS_VGET for the
* inode associated with ".." returns. We hope that this occurs
* infrequently since we cannot avoid this race condition without
* implementing a sophisticated deadlock detection algorithm.
* Note also that this simple deadlock detection scheme will not
* work if the filesystem has any hard links other than ".."
* that point backwards in the directory structure.
*/
pdp = vdp;
if (flags & ISDOTDOT) {
VOP_UNLOCK(pdp, 0);
error = deget(pmp, cluster, blkoff, &tdp);
vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY);
error = msdosfs_deget_dotdot(pdp, cluster, blkoff, vpp);
if (error)
return (error);
*vpp = DETOV(tdp);
/*
* Recheck that ".." still points to the inode we
* looked up before pdp lock was dropped.
*/
error = msdosfs_lookup_(pdp, NULL, cnp, &inode1);
if (error) {
vput(*vpp);
return (error);
}
if (VTODE(*vpp)->de_inode != inode1) {
vput(*vpp);
goto restart;
}
} else if (dp->de_StartCluster == scn && isadir) {
VREF(vdp); /* we want ourself, ie "." */
*vpp = vdp;
@ -542,6 +557,49 @@ msdosfs_lookup(ap)
return (0);
}
static int
msdosfs_deget_dotdot(struct vnode *vp, u_long cluster, int blkoff,
struct vnode **rvp)
{
struct mount *mp;
struct msdosfsmount *pmp;
struct denode *rdp;
int ltype, error;
mp = vp->v_mount;
pmp = VFSTOMSDOSFS(mp);
ltype = VOP_ISLOCKED(vp);
KASSERT(ltype == LK_EXCLUSIVE || ltype == LK_SHARED,
("msdosfs_deget_dotdot: vp not locked"));
error = vfs_busy(mp, MBF_NOWAIT);
if (error != 0) {
vfs_ref(mp);
VOP_UNLOCK(vp, 0);
error = vfs_busy(mp, 0);
vn_lock(vp, ltype | LK_RETRY);
vfs_rel(mp);
if (error != 0)
return (ENOENT);
if (vp->v_iflag & VI_DOOMED) {
vfs_unbusy(mp);
return (ENOENT);
}
}
VOP_UNLOCK(vp, 0);
error = deget(pmp, cluster, blkoff, &rdp);
vfs_unbusy(mp);
if (error == 0)
*rvp = DETOV(rdp);
vn_lock(vp, ltype | LK_RETRY);
if (vp->v_iflag & VI_DOOMED) {
if (error == 0)
vput(*rvp);
error = ENOENT;
}
return (error);
}
/*
* dep - directory entry to copy into the directory
* ddep - directory to add to