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Date: Wed, 13 Apr 2005 18:31:17 -0400 (EDT)
From: Jeff Roberson <jroberson@chesapeake.net>
To: Alfred Perlstein <alfred@FreeBSD.org>
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cc: cvs-src@FreeBSD.org
cc: Jeff Roberson <jeff@FreeBSD.org>
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Subject: Re: cvs commit: src/sys/coda coda_vnops.c src/sys/compat/linux
 linux_getcwd.c src/sys/fs/devfs devfs_vnops.c src/sys/fs/hpfs hpfs_vnops.c
 src/sys/fs/msdosfs msdosfs_lookup.c src/sys/fs/nwfs nwfs_vnops
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On Wed, 13 Apr 2005, Alfred Perlstein wrote:

> * Jeff Roberson <jeff@FreeBSD.org> [050413 03:59] wrote:
> > jeff        2005-04-13 10:59:10 UTC
> >
> >   FreeBSD src repository
> >
> >   Modified files:
> >     sys/coda             coda_vnops.c
> >     sys/compat/linux     linux_getcwd.c
> >   Log:
> >    - Change all filesystems and vfs_cache to relock the dvp once the child is
> >      locked in the ISDOTDOT case.  Se vfs_lookup.c r1.79 for details.
>
> Sorry to bumble into your way, but can you explain this?  I thought
> the lock order was always dvp->vp, doing a vp->dvp lock is a reversal
> and can cause deadlock.  I guess I'm missing something, can you explain
> please?

For ISDOTDOT dvp is really the child of vp.  For example

a/b/c

b/.. is a, and a must be locked before b.  So b must be unlocked before we
can lock ..(a), and then b must be locked again.

>
> --
> - Alfred Perlstein
> - email: bright@mu.org cell: 408-480-4684
>