Date: Tue, 3 Aug 2021 09:52:46 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 0a4eb4d65c11 - stable/13 - null_bypass(): prevent loosing the only reference to the lower vnode Message-ID: <202108030952.1739qkUc081333@gitrepo.freebsd.org>
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The branch stable/13 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=0a4eb4d65c11dc775733dd5a0a470419e1376515 commit 0a4eb4d65c11dc775733dd5a0a470419e1376515 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2021-07-20 00:53:08 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2021-08-03 09:52:35 +0000 null_bypass(): prevent loosing the only reference to the lower vnode (cherry picked from commit d5b078163e0d6bb2fe36f8e49a44853908d5e2db) --- sys/fs/nullfs/null_vnops.c | 25 ++++++++++++++++++++----- 1 file changed, 20 insertions(+), 5 deletions(-) diff --git a/sys/fs/nullfs/null_vnops.c b/sys/fs/nullfs/null_vnops.c index 4dfc5efaf9ed..03f8b0dcbf7d 100644 --- a/sys/fs/nullfs/null_vnops.c +++ b/sys/fs/nullfs/null_vnops.c @@ -266,6 +266,17 @@ null_bypass(struct vop_generic_args *ap) old_vps[i] = *this_vp_p; *(vps_p[i]) = NULLVPTOLOWERVP(*this_vp_p); + /* + * The upper vnode reference to the lower + * vnode is the only reference that keeps our + * pointer to the lower vnode alive. If lower + * vnode is relocked during the VOP call, + * upper vnode might become unlocked and + * reclaimed, which invalidates our reference. + * Add a transient hold around VOP call. + */ + vhold(*this_vp_p); + /* * XXX - Several operations have the side effect * of vrele'ing their vp's. We must account for @@ -300,6 +311,7 @@ null_bypass(struct vop_generic_args *ap) lvp = *(vps_p[i]); /* + * Get rid of the transient hold on lvp. * If lowervp was unlocked during VOP * operation, nullfs upper vnode could have * been reclaimed, which changes its v_vnlock @@ -307,11 +319,14 @@ null_bypass(struct vop_generic_args *ap) * 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); + if (lvp != NULLVP) { + if (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); + } + vdrop(lvp); } *(vps_p[i]) = old_vps[i];
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