On Sun, Dec 23, 2007 at 10:20:31AM +1100, Bruce Evans wrote: > On Sat, 22 Dec 2007, Kostik Belousov wrote: > >Ok, since you talked about this first :). I already made the following > >patch, but did not published it since I still did not inspected all > >callers of MNT_VNODE_FOREACH() for safety of dropping mount interlock. > >It shall be safe, but better to check. Also, I postponed the check > >until it was reported that yielding does solve the original problem. > > Good. I'd still like to unobfuscate the function call. What do you mean there ?
> Putting the count in the union seems fragile at best. Even if nothing
> can access the marker vnode, you need to context-switch its old contents
> while using it for the count, in case its old contents is used. Vnode-
> printing routines might still be confused.
Could you, please, describe what you mean by "contex-switch" for the
VMARKER ?
Mark, could you, please, retest the patch below in your setup ?
I want to put a change or some edition of it into the 7.0 release, and
we need to move fast to do this.
diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index 14acc5b..046af82 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -1994,6 +1994,12 @@ __mnt_vnode_next(struct vnode **mvp, struct mount *mp)
mtx_assert(MNT_MTX(mp), MA_OWNED);
KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
+ if ((*mvp)->v_yield++ == 500) {
+ MNT_IUNLOCK(mp);
+ (*mvp)->v_yield = 0;
+ uio_yield();
+ MNT_ILOCK(mp);
+ }
vp = TAILQ_NEXT(*mvp, v_nmntvnodes);
while (vp != NULL && vp->v_type == VMARKER)
vp = TAILQ_NEXT(vp, v_nmntvnodes);
diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
index dc70417..6e3119b 100644
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -131,6 +131,7 @@ struct vnode {
struct socket *vu_socket; /* v unix domain net (VSOCK) */
struct cdev *vu_cdev; /* v device (VCHR, VBLK) */
struct fifoinfo *vu_fifoinfo; /* v fifo (VFIFO) */
+ int vu_yield; /* yield count (VMARKER) */
} v_un;
/*
@@ -185,6 +186,7 @@ struct vnode {
#define v_socket v_un.vu_socket
#define v_rdev v_un.vu_cdev
#define v_fifoinfo v_un.vu_fifoinfo
+#define v_yield v_un.vu_yield
/* XXX: These are temporary to avoid a source sweep at this time */
#define v_object v_bufobj.bo_object
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