Date: Fri, 07 Aug 2026 09:10:06 +0000 From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 9f5c4ef32812 - main - dounmount(9): temporarily enable recursion for the covered vnode lock Message-ID: <6a75a0ee.1c782.5e203c3e@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=9f5c4ef32812afb4573a278e6eafe5040f839d13 commit 9f5c4ef32812afb4573a278e6eafe5040f839d13 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2026-07-31 04:12:17 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2026-08-07 09:09:50 +0000 dounmount(9): temporarily enable recursion for the covered vnode lock For some complex nullfs mount configurations, it is possible to get the covered vnode lock for the mount shared with some inside-mount vnode lock. Then at unmount time, vflush() would recurse on the covered vnode lock when reclaiming the vnode. Work around it, by temprorarily allowing recursion on the covered vnode lock. Disable recursion after the unmount if it was not enabled before. PR: 297174 Reviewed by: jah Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D58567 --- sys/kern/vfs_mount.c | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-) diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c index f123c59981c4..90215a64b08b 100644 --- a/sys/kern/vfs_mount.c +++ b/sys/kern/vfs_mount.c @@ -1880,7 +1880,8 @@ vfs_check_usecounts(struct mount *mp) } static void -dounmount_cleanup(struct mount *mp, struct vnode *coveredvp, int mntkflags) +dounmount_cleanup(struct mount *mp, struct vnode *coveredvp, int mntkflags, + bool disablerec) { mtx_assert(MNT_MTX(mp), MA_OWNED); @@ -1892,6 +1893,8 @@ dounmount_cleanup(struct mount *mp, struct vnode *coveredvp, int mntkflags) vfs_op_exit_locked(mp); MNT_IUNLOCK(mp); if (coveredvp != NULL) { + if (disablerec) + VN_LOCK_DREC(coveredvp); VOP_UNLOCK(coveredvp); vdrop(coveredvp); } @@ -2193,6 +2196,7 @@ dounmount(struct mount *mp, uint64_t flags, struct thread *td) uint64_t async_flag; int mnt_gen_r; unsigned int retries; + bool coveredrec; KASSERT((flags & MNT_DEFERRED) == 0 || (flags & (MNT_RECURSE | MNT_FORCE)) == (MNT_RECURSE | MNT_FORCE), @@ -2301,6 +2305,7 @@ dounmount(struct mount *mp, uint64_t flags, struct thread *td) if ((flags & MNT_DEFERRED) != 0) vfs_ref(mp); + coveredrec = false; if ((coveredvp = mp->mnt_vnodecovered) != NULL) { mnt_gen_r = mp->mnt_gen; VI_LOCK(coveredvp); @@ -2317,6 +2322,19 @@ dounmount(struct mount *mp, uint64_t flags, struct thread *td) vfs_rel(mp); return (EBUSY); } + + /* + * For some complex nullfs mount configurations, it is + * possible to get the covered vnode lock for the + * mount shared with some inside-mount vnode lock. + * Then at unmount time, vflush() would recurse on the + * covered vnode lock when reclaiming the vnode. + * + * To work around it, temprorarily allow recursion for + * the covered vnode lock. + */ + coveredrec = VN_LOCK_CANREC(coveredvp); + VN_LOCK_AREC(coveredvp); } vfs_op_enter(mp); @@ -2326,7 +2344,7 @@ dounmount(struct mount *mp, uint64_t flags, struct thread *td) if ((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0 || (mp->mnt_flag & MNT_UPDATE) != 0 || !TAILQ_EMPTY(&mp->mnt_uppers)) { - dounmount_cleanup(mp, coveredvp, 0); + dounmount_cleanup(mp, coveredvp, 0, !coveredrec); return (EBUSY); } mp->mnt_kern_flag |= MNTK_UNMOUNT; @@ -2339,7 +2357,8 @@ dounmount(struct mount *mp, uint64_t flags, struct thread *td) MNT_ILOCK(mp); if (error != 0) { vn_seqc_write_end(coveredvp); - dounmount_cleanup(mp, coveredvp, MNTK_UNMOUNT); + dounmount_cleanup(mp, coveredvp, MNTK_UNMOUNT, + !coveredrec); if (rootvp != NULL) { vn_seqc_write_end(rootvp); vrele(rootvp); @@ -2425,6 +2444,8 @@ dounmount(struct mount *mp, uint64_t flags, struct thread *td) MNT_IUNLOCK(mp); if (coveredvp) { vn_seqc_write_end(coveredvp); + if (!coveredrec) + VN_LOCK_DREC(coveredvp); VOP_UNLOCK(coveredvp); vdrop(coveredvp); } @@ -2445,6 +2466,8 @@ dounmount(struct mount *mp, uint64_t flags, struct thread *td) coveredvp->v_mountedhere = NULL; vn_seqc_write_end_locked(coveredvp); VI_UNLOCK(coveredvp); + if (!coveredrec) + VN_LOCK_DREC(coveredvp); VOP_UNLOCK(coveredvp); vdrop(coveredvp); }home | help
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