cvs commit: src/sys/kern vfs_lookup.c

[Alexander Kabaev]

On Tue, 30 Aug 2005 15:47:04 -0700
Alfred Perlstein <alfred at freebsd.org> wrote:

> Ok, maybe I'm missing something, but...
> 
> 	while (dp->v_type == VDIR && (mp = dp->v_mountedhere) &&
> 	       (cnp->cn_flags & NOCROSSMOUNT) == 0) {
> 		KASSERT(dp != ndp->ni_dvp, ("XXX"));
> 		if (vfs_busy(mp, 0, 0, td))
> 			continue;
> here ->>>	vput(dp);
> 		tvfslocked = VFS_LOCK_GIANT(mp);
> 		VFS_UNLOCK_GIANT(vfslocked);
> 		vfslocked = tvfslocked;
> 		VOP_UNLOCK(ndp->ni_dvp, 0, td);
> 		error = VFS_ROOT(mp, cnp->cn_lkflags, &tdp, td);
> 		VOP_LOCK(ndp->ni_dvp, cnp->cn_lkflags | LK_RETRY, td);
> 		vfs_unbusy(mp, td);
> 		if (error) {
> 			dpunlocked = 1;
> 			goto bad2;
> 		}
> 		ndp->ni_vp = dp = tdp;
> 	}
> 
> Isn't dp already unlocked here?  vput should be unlocking the vnode
> and we have the above KASSERT showing that they should be the same
> vnode...

dp != ndp->ni_dvp at that point. If we have amd serving /home,

ndp->ni_dvp is '/' directory
dp is /home directory  

Having / locked while waiting for VFS_ROOT on amd filesystem serves no
purpose.

> Also, I think lockparent doesn't need to be respected because
> we're trading parent vnodes.  Basically, we're hitting a vnode
> that has another vnode stacked on it (root vnode), and switching to
> it. we're not actually decending.
> 
> Is this OK?
> 
> -Alfred
> 
> 
> 
> * Alexander Kabaev <kan at FreeBSD.org> [050830 09:12] wrote:
> > kan         2005-08-30 16:12:03 UTC
> > 
> >   FreeBSD src repository
> > 
> >   Modified files:        (Branch: RELENG_6)
> >     sys/kern             vfs_lookup.c 
> >   Log:
> >   MFC r1.81:
> >   Do not keep parent directory locked while calling VFS_ROOT to
> >   traverse mount points in lookup(). The lock can be dropped safely
> >   around VFS_ROOT because LOCKPARENT semantics with child and parent
> >   vnodes coming from different FSes does not really have any
> > meaningful use and we do not really care about parent state after
> > we relock it. This prevents easily triggered deadlock on systems
> > using automounter daemon.
> >   
> >   Approved by:    re (scottl)
> >   
> >   Revision  Changes    Path
> >   1.80.2.1  +2 -0      src/sys/kern/vfs_lookup.c
> 
> -- 
> - Alfred Perlstein


-- 
Alexander Kabaev
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