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nullfs: ensure correct lock is taken after bypass.

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If lower VOP relocked the lower vnode, it is possible that nullfs
vnode was reclaimed meantime.  In this case nullfs vnode no longer
shares lock with lower vnode, which breaks locking protocol.

Check for the condition and acquire nullfs vnode lock if detected.

Reported and tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2020-10-19 19:23:22 +00:00
parent c0baa3dc4a
commit 6b56b0ca93
1 changed files with 18 additions and 0 deletions
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18
sys/fs/nullfs/null_vnops.c
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@ -227,6 +227,7 @@ null_bypass(struct vop_generic_args *ap)
struct vnode *old_vps[VDESC_MAX_VPS];
struct vnode **vps_p[VDESC_MAX_VPS];
struct vnode ***vppp;
struct vnode *lvp;
struct vnodeop_desc *descp = ap->a_desc;
int reles, i;
@ -295,6 +296,23 @@ null_bypass(struct vop_generic_args *ap)
if (descp->vdesc_vp_offsets[i] == VDESC_NO_OFFSET)
break; /* bail out at end of list */
if (old_vps[i]) {
lvp = *(vps_p[i]);
/*
* If lowervp was unlocked during VOP
* operation, nullfs upper vnode could have
* been reclaimed, which changes its v_vnlock
* back to private v_lock. In this case we
* must move lock ownership from lower to
* upper (reclaimed) vnode.
*/
if (lvp != NULLVP &&
VOP_ISLOCKED(lvp) == LK_EXCLUSIVE &&
old_vps[i]->v_vnlock != lvp->v_vnlock) {
VOP_UNLOCK(lvp);
VOP_LOCK(old_vps[i], LK_EXCLUSIVE | LK_RETRY);
}
*(vps_p[i]) = old_vps[i];
#if 0
if (reles & VDESC_VP0_WILLUNLOCK)