On Sun, Jun 03, 2018 at 10:37:30AM -0700, Philip Guenther wrote:
> Diff below adds VB_DUPOK to indicate that a given vfs_busy() call is
> expected/permitted to occur while the thread already holds another
> filesystem busy; the caller is responsible for ensuring the filesystems
> are locked in the correct order (or that NOWAIT is used safely as in the
> sys_mount() case).
>
> As part of this, this plumbs RW_DUPOK for rw_enter().
>
> I no longer get the witness warning on hibernate with this.
>
> ok?
OK bluhm@
> Index: sys/mount.h
> ===================================================================
> RCS file: /data/src/openbsd/src/sys/sys/mount.h,v
> retrieving revision 1.136
> diff -u -p -r1.136 mount.h
> --- sys/mount.h 8 May 2018 08:58:49 -0000 1.136
> +++ sys/mount.h 3 Jun 2018 17:05:28 -0000
> @@ -564,6 +564,7 @@ int vfs_busy(struct mount *, int);
> #define VB_WRITE 0x02
> #define VB_NOWAIT 0x04 /* immediately fail on busy lock */
> #define VB_WAIT 0x08 /* sleep fail on busy lock */
> +#define VB_DUPOK 0x10 /* permit duplicate mount busying */
>
> int vfs_isbusy(struct mount *);
> int vfs_mount_foreach_vnode(struct mount *, int (*func)(struct vnode *,
> Index: sys/rwlock.h
> ===================================================================
> RCS file: /data/src/openbsd/src/sys/sys/rwlock.h,v
> retrieving revision 1.22
> diff -u -p -r1.22 rwlock.h
> --- sys/rwlock.h 12 Aug 2017 23:27:44 -0000 1.22
> +++ sys/rwlock.h 3 Jun 2018 17:05:32 -0000
> @@ -116,6 +116,7 @@ struct rwlock {
> #define RW_SLEEPFAIL 0x0020UL /* fail if we slept for the lock */
> #define RW_NOSLEEP 0x0040UL /* don't wait for the lock */
> #define RW_RECURSEFAIL 0x0080UL /* Fail on recursion for RRW
> locks. */
> +#define RW_DUPOK 0x0100UL /* Permit duplicate lock */
>
> /*
> * for rw_status() and rrw_status() only: exclusive lock held by
> Index: kern/kern_rwlock.c
> ===================================================================
> RCS file: /data/src/openbsd/src/sys/kern/kern_rwlock.c,v
> retrieving revision 1.35
> diff -u -p -r1.35 kern_rwlock.c
> --- kern/kern_rwlock.c 21 Mar 2018 12:28:39 -0000 1.35
> +++ kern/kern_rwlock.c 3 Jun 2018 17:00:02 -0000
> @@ -223,6 +223,8 @@ _rw_enter(struct rwlock *rwl, int flags
> lop_flags = LOP_NEWORDER;
> if (flags & RW_WRITE)
> lop_flags |= LOP_EXCLUSIVE;
> + if (flags & RW_DUPOK)
> + lop_flags |= LOP_DUPOK;
> if ((flags & RW_NOSLEEP) == 0 && (flags & RW_DOWNGRADE) == 0)
> WITNESS_CHECKORDER(&rwl->rwl_lock_obj, lop_flags, file, line,
> NULL);
> Index: kern/vfs_subr.c
> ===================================================================
> RCS file: /data/src/openbsd/src/sys/kern/vfs_subr.c,v
> retrieving revision 1.273
> diff -u -p -r1.273 vfs_subr.c
> --- kern/vfs_subr.c 27 May 2018 06:02:14 -0000 1.273
> +++ kern/vfs_subr.c 3 Jun 2018 17:04:09 -0000
> @@ -188,6 +188,11 @@ vfs_busy(struct mount *mp, int flags)
> else
> rwflags |= RW_NOSLEEP;
>
> +#ifdef WITNESS
> + if (flags & VB_DUPOK)
> + rwflags |= RW_DUPOK;
> +#endif
> +
> if (rw_enter(&mp->mnt_lock, rwflags))
> return (EBUSY);
>
> @@ -1602,7 +1607,7 @@ vfs_stall(struct proc *p, int stall)
> */
> TAILQ_FOREACH_REVERSE(mp, &mountlist, mntlist, mnt_list) {
> if (stall) {
> - error = vfs_busy(mp, VB_WRITE|VB_WAIT);
> + error = vfs_busy(mp, VB_WRITE|VB_WAIT|VB_DUPOK);
> if (error) {
> printf("%s: busy\n", mp->mnt_stat.f_mntonname);
> allerror = error;
> Index: kern/vfs_syscalls.c
> ===================================================================
> RCS file: /data/src/openbsd/src/sys/kern/vfs_syscalls.c,v
> retrieving revision 1.284
> diff -u -p -r1.284 vfs_syscalls.c
> --- kern/vfs_syscalls.c 2 Jun 2018 10:27:43 -0000 1.284
> +++ kern/vfs_syscalls.c 3 Jun 2018 17:04:55 -0000
> @@ -230,7 +230,7 @@ sys_mount(struct proc *p, void *v, regis
>
> update:
> /* Ensure that the parent mountpoint does not get unmounted. */
> - error = vfs_busy(vp->v_mount, VB_READ|VB_NOWAIT);
> + error = vfs_busy(vp->v_mount, VB_READ|VB_NOWAIT|VB_DUPOK);
> if (error) {
> if (mp->mnt_flag & MNT_UPDATE) {
> mp->mnt_flag = mntflag;
> @@ -439,7 +439,7 @@ dounmount(struct mount *mp, int flags, s
> error = EBUSY;
> goto err;
> }
> - error = vfs_busy(mp, VB_WRITE|VB_WAIT);
> + error = vfs_busy(mp, VB_WRITE|VB_WAIT|VB_DUPOK);
> if (error) {
> if ((flags & MNT_DOOMED)) {
> /*
