Date: Tue, 17 Feb 2026 23:01:27 +0000 From: Rick Macklem <rmacklem@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 935cf3284f52 - main - vfs_mount.c: Don't call VFS_MOUNT() if only exports are being updated Message-ID: <6994f347.34832.52d33fe@gitrepo.freebsd.org>
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The branch main has been updated by rmacklem: URL: https://cgit.FreeBSD.org/src/commit/?id=935cf3284f520c90a63baaadb762caaa30084f5c commit 935cf3284f520c90a63baaadb762caaa30084f5c Author: Rick Macklem <rmacklem@FreeBSD.org> AuthorDate: 2026-02-17 22:57:42 +0000 Commit: Rick Macklem <rmacklem@FreeBSD.org> CommitDate: 2026-02-17 22:59:57 +0000 vfs_mount.c: Don't call VFS_MOUNT() if only exports are being updated PR#293198 reports a hang within ZFS when exports are being updated concurrently with a VOP_SETEXTATTR(). The hang appears to be caused by mishandling of the z_teardown_lock, but fixing handling of this lock appears to be a major effort. Since the hang occurs when VFS_MOUNT() acquires a write/exclusive z_teardown_lock, which rarely occurs, except when exports are being updated, this patch avoids the VFS_MOUNT() call for this case. Avoiding a VFS_MOUNT() call fixes the hang for the case reported by PR#293198 and is also an optimization. As such, this patch avoids the VFS_MOUNT() call when only exports are being updated similar to what was already being done within vnet prisons. PR: 293198 Reviewed by: kib, markj MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D55318 --- sys/kern/vfs_mount.c | 52 +++++++++++++++++++++++++++++++--------------------- 1 file changed, 31 insertions(+), 21 deletions(-) diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c index 2237fcc6b423..383ccf98c10e 100644 --- a/sys/kern/vfs_mount.c +++ b/sys/kern/vfs_mount.c @@ -74,7 +74,7 @@ #define VFS_MOUNTARG_SIZE_MAX (1024 * 64) static int vfs_domount(struct thread *td, const char *fstype, char *fspath, - uint64_t fsflags, bool jail_export, + uint64_t fsflags, bool only_export, bool jail_export, struct vfsoptlist **optlist); static void free_mntarg(struct mntarg *ma); @@ -806,7 +806,7 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions) struct vfsopt *opt, *tmp_opt; char *fstype, *fspath, *errmsg; int error, fstypelen, fspathlen, errmsg_len, errmsg_pos; - bool autoro, has_nonexport, jail_export; + bool autoro, has_nonexport, only_export, jail_export; errmsg = fspath = NULL; errmsg_len = fspathlen = 0; @@ -861,12 +861,11 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions) * when we want to update the root filesystem. */ has_nonexport = false; - jail_export = false; + only_export = false; TAILQ_FOREACH_SAFE(opt, optlist, link, tmp_opt) { int do_freeopt = 0; - if (jailed(td->td_ucred) && - strcmp(opt->name, "export") != 0 && + if (strcmp(opt->name, "export") != 0 && strcmp(opt->name, "update") != 0 && strcmp(opt->name, "fstype") != 0 && strcmp(opt->name, "fspath") != 0 && @@ -957,7 +956,7 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions) fsflags |= MNT_UNION; else if (strcmp(opt->name, "export") == 0) { fsflags |= MNT_EXPORTED; - jail_export = true; + only_export = true; } else if (strcmp(opt->name, "automounted") == 0) { fsflags |= MNT_AUTOMOUNTED; do_freeopt = 1; @@ -989,14 +988,22 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions) } /* - * If has_nonexport is true or the caller is not running within a - * vnet prison that can run mountd(8), set jail_export false. + * only_export is set to true only if exports are being + * updated and nothing else is being updated. + */ + if (has_nonexport) + only_export = false; + /* + * If only_export is true and the caller is running within a + * vnet prison that can run mountd(8), set jail_export true. */ - if (has_nonexport || !jailed(td->td_ucred) || - !prison_check_nfsd(td->td_ucred)) - jail_export = false; + jail_export = false; + if (only_export && jailed(td->td_ucred) && + prison_check_nfsd(td->td_ucred)) + jail_export = true; - error = vfs_domount(td, fstype, fspath, fsflags, jail_export, &optlist); + error = vfs_domount(td, fstype, fspath, fsflags, only_export, + jail_export, &optlist); if (error == ENODEV) { error = EINVAL; if (errmsg != NULL) @@ -1014,8 +1021,8 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions) printf("%s: R/W mount failed, possibly R/O media," " trying R/O mount\n", __func__); fsflags |= MNT_RDONLY; - error = vfs_domount(td, fstype, fspath, fsflags, jail_export, - &optlist); + error = vfs_domount(td, fstype, fspath, fsflags, only_export, + jail_export, &optlist); } bail: /* copyout the errmsg */ @@ -1307,6 +1314,7 @@ vfs_domount_update( struct thread *td, /* Calling thread. */ struct vnode *vp, /* Mount point vnode. */ uint64_t fsflags, /* Flags common to all filesystems. */ + bool only_export, /* Got export option. */ bool jail_export, /* Got export option in vnet prison. */ struct vfsoptlist **optlist /* Options local to the filesystem. */ ) @@ -1442,15 +1450,16 @@ vfs_domount_update( * get. No freeing of cn_pnbuf. */ /* + * When only updating mount exports, VFS_MOUNT() does not need to + * be called, as indicated by only_export being set true. * For the case of mountd(8) doing exports from within a vnet jail, * "from" is typically not set correctly such that VFS_MOUNT() will - * return ENOENT. It is not obvious that VFS_MOUNT() ever needs to be - * called when mountd is doing exports, but this check only applies to - * the specific case where it is running inside a vnet jail, to - * avoid any POLA violation. + * return ENOENT. For ZFS, there is a locking bug which can result in + * deadlock if VFS_MOUNT() is called when extended attributes are + * being updated. */ error = 0; - if (!jail_export) + if (!only_export) error = VFS_MOUNT(mp); export_error = 0; @@ -1590,6 +1599,7 @@ vfs_domount( const char *fstype, /* Filesystem type. */ char *fspath, /* Mount path. */ uint64_t fsflags, /* Flags common to all filesystems. */ + bool only_export, /* Got export option. */ bool jail_export, /* Got export option in vnet prison. */ struct vfsoptlist **optlist /* Options local to the filesystem. */ ) @@ -1693,8 +1703,8 @@ vfs_domount( } free(pathbuf, M_TEMP); } else - error = vfs_domount_update(td, vp, fsflags, jail_export, - optlist); + error = vfs_domount_update(td, vp, fsflags, only_export, + jail_export, optlist); out: NDFREE_PNBUF(&nd);home | help
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