On Sun, 3 Jun 2018, Theo de Raadt wrote: > Philip Guenther <guent...@gmail.com> wrote: > > The warning is not that a single filesystem is being locked > > recursively by a single thread, but just that a single thread is > > holding locks on multiple filesystems. > > vfs_stall() needs to grab locks on all filesystems, to stop a variety of > filesystem transactions. (Other types of transactions are blocked in > other ways). > > sys_umount() grabs locks on all filesystems above it, to stop anyone > from doing a parallel mount/unmount along the same path. > > This is all normal.
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? Philip Guenther 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)) { /*