Date: Sat, 21 Aug 2004 19:41:16 -0400 From: Brian Fundakowski Feldman <green@FreeBSD.org> To: Alan Cox <alc@cs.rice.edu> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/vm vm_fault.c Message-ID: <20040821234116.GC784@green.homeunix.org> In-Reply-To: <20040821233134.GF9106@cs.rice.edu> References: <200408211920.i7LJKLlA088634@repoman.freebsd.org> <20040821225939.GA784@green.homeunix.org> <20040821233134.GF9106@cs.rice.edu>
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On Sat, Aug 21, 2004 at 06:31:34PM -0500, Alan Cox wrote:
> On Sat, Aug 21, 2004 at 06:59:39PM -0400, Brian Fundakowski Feldman wrote:
> > On Sat, Aug 21, 2004 at 07:20:21PM +0000, Alan Cox wrote:
> > > alc 2004-08-21 19:20:21 UTC
> > >
> > > FreeBSD src repository
> > >
> > > Modified files:
> > > sys/vm vm_fault.c
> > > Log:
> > > Further reduce the use of Giant by vm_fault(): Giant is held only when
> > > manipulating a vnode, e.g., calling vput(). This reduces contention for
> > > Giant during many copy-on-write faults, resulting in some additional
> > > speedup on SMPs.
> > >
> > > Note: debug_mpsafevm must be enabled for this optimization to take effect.
> >
> > This is very broken. See included first attempt at fixing it without
> > regard for actually trying to reimplement debug.mpsafenet for vnodes.
> >
>
> Can you please explain what is broken?
#1. Lock order reversal. Giant is acquired after the map read lock.
#2. Unlocking Giant without it being locked. This occurs in both
VM_UNLOCK_GIANT() lines I removed. I know this because my machine
panicked on the other after I removed the first.
--
Brian Fundakowski Feldman \'[ FreeBSD ]''''''''''\
<> green@FreeBSD.org \ The Power to Serve! \
Opinions expressed are my own. \,,,,,,,,,,,,,,,,,,,,,,\
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