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unionfs: various locking fixes

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--Clearing cached subdirectories in unionfs_noderem() should be done
  under the vnode interlock

--When preparing to switch the vnode lock in both unionfs_node_update()
  and unionfs_noderem(), the incoming lock should be acquired before
  updating the v_vnlock field to point to it.  Otherwise we effectively
  break the locking contract for a brief window.

Reviewed by:	kib
Differential Revision: https://reviews.freebsd.org/D32629
This commit is contained in:
Jason A. Harmening 2021-10-24 10:24:18 -07:00
parent acdfc09639
commit 866dd6335a
1 changed files with 24 additions and 15 deletions
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39
sys/fs/unionfs/union_subr.c
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@ -439,6 +439,9 @@ unionfs_noderem(struct vnode *vp, struct thread *td)
struct vnode *dvp;
int count;
if (lockmgr(&(vp->v_lock), LK_EXCLUSIVE, NULL) != 0)
panic("the lock for deletion is unacquirable.");
/*
* Use the interlock to protect the clearing of v_data to
* prevent faults in unionfs_lock().
@ -459,6 +462,22 @@ unionfs_noderem(struct vnode *vp, struct thread *td)
VOP_ADD_WRITECOUNT(lvp, -vp->v_writecount);
} else if (vp->v_writecount < 0)
vp->v_writecount = 0;
if (unp->un_hashtbl != NULL) {
/*
* Clear out any cached child vnodes. This should only
* be necessary during forced unmount, when the vnode may
* be reclaimed with a non-zero use count. Otherwise the
* reference held by each child should prevent reclamation.
*/
for (count = 0; count <= UNIONFSHASHMASK; count++) {
hd = unp->un_hashtbl + count;
LIST_FOREACH_SAFE(unp_t1, hd, un_hash, unp_t2) {
LIST_REMOVE(unp_t1, un_hash);
unp_t1->un_hash.le_next = NULL;
unp_t1->un_hash.le_prev = NULL;
}
}
}
VI_UNLOCK(vp);
if (lvp != NULLVP)
@ -469,9 +488,6 @@ unionfs_noderem(struct vnode *vp, struct thread *td)
if (dvp != NULLVP)
unionfs_rem_cached_vnode(unp, dvp);
if (lockmgr(vp->v_vnlock, LK_EXCLUSIVE, VI_MTX(vp)) != 0)
panic("the lock for deletion is unacquirable.");
if (lvp != NULLVP)
vrele(lvp);
if (uvp != NULLVP)
@ -483,14 +499,6 @@ unionfs_noderem(struct vnode *vp, struct thread *td)
}
if (unp->un_hashtbl != NULL) {
for (count = 0; count <= UNIONFSHASHMASK; count++) {
hd = unp->un_hashtbl + count;
LIST_FOREACH_SAFE(unp_t1, hd, un_hash, unp_t2) {
LIST_REMOVE(unp_t1, un_hash);
unp_t1->un_hash.le_next = NULL;
unp_t1->un_hash.le_prev = NULL;
}
}
hashdestroy(unp->un_hashtbl, M_UNIONFSHASH, UNIONFSHASHMASK);
}
@ -798,15 +806,16 @@ unionfs_node_update(struct unionfs_node *unp, struct vnode *uvp,
dvp = unp->un_dvp;
/*
* lock update
* Uppdate the upper vnode's lock state to match the lower vnode,
* and then switch the unionfs vnode's lock to the upper vnode.
*/
lockrec = lvp->v_vnlock->lk_recurse;
for (count = 0; count < lockrec; count++)
vn_lock(uvp, LK_EXCLUSIVE | LK_CANRECURSE | LK_RETRY);
VI_LOCK(vp);
unp->un_uppervp = uvp;
vp->v_vnlock = uvp->v_vnlock;
VI_UNLOCK(vp);
lockrec = lvp->v_vnlock->lk_recurse;
for (count = 0; count < lockrec; count++)
vn_lock(uvp, LK_EXCLUSIVE | LK_CANRECURSE | LK_RETRY);
/*
* Re-cache the unionfs vnode against the upper vnode