From owner-freebsd-bugs  Mon Jul 24 08:59:42 1995
Return-Path: bugs-owner
Received: (from majordom@localhost)
          by freefall.cdrom.com (8.6.11/8.6.6) id IAA24501
          for bugs-outgoing; Mon, 24 Jul 1995 08:59:42 -0700
Received: (from dyson@localhost)
          by freefall.cdrom.com (8.6.11/8.6.6) id IAA24492
          ; Mon, 24 Jul 1995 08:59:42 -0700
From: John Dyson <dyson>
Message-Id: <199507241559.IAA24492@freefall.cdrom.com>
Subject: Re: brelse() panic in nfs_read()/nfs_bioread()
To: dfr@render.com (Doug Rabson)
Date: Mon, 24 Jul 1995 08:59:41 -0700 (PDT)
Cc: dillon@blob.best.net, bugs@freebsd.org
In-Reply-To: <Pine.BSF.3.91.950724150529.12542F-100000@minnow.render.com> from "Doug Rabson" at Jul 24, 95 03:11:49 pm
X-Mailer: ELM [version 2.4 PL24]
Content-Type: text
Content-Length: 689       
Sender: bugs-owner@freebsd.org
Precedence: bulk

> 
> I am mystified by this one.  It looks as if the VM system has helpfully 
> reallocated one of the pages associated with the buffer between starting 
> the read and releasing the buffer.  This should be impossible, as the 
DG and I have been working this problem for the last few days.  It is
indeed subtile... (Actually a similar one -- probably the same cause.)

> pages are marked busy (vfs_busy_pages(bp, 0)) and the buffer is busy 
> (B_BUSY is set).  I don't really understand this bogus_page stuff; can 
> someone explain it to me?
> 
The bogus page stuff is used to keep modified pages that might have
lost their association with a buffer from being lost.

John
dyson@root.com