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To: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
cc: swallace@ece.uci.edu, current@FreeBSD.ORG
Subject: Re: exec bug 
In-reply-to: Your message of "Sun, 26 Jan 1997 13:00:03 +0100."
             <199701261200.NAA27988@labinfo.iet.unipi.it> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Sun, 26 Jan 1997 05:36:03 -0800
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>> >> >execve() maps the first page to memory and calls exec_aout_imgact()
>> >> >which then accesses this page and fails.  The system then gets
>> >> >a page fault while in kernel mode and dies.
>> >
>> >Given this description, would this also occur when trying to run
>> >a program from an nfs-mounted partition which at some point becomes
>> >unavailable ? If not (as I hope!) what is the difference ?
>> 
>>    In the case of NFS, the read should block indefinately. I'm not sure what
>> will happen if the NFS is mounted "soft", however.
>
>that would be a major problem then!

   Not any more so than any other read blocking indefinately.

> Wouldn't it be possible to track
>the exact reason of the fault inside the handler and avoid panicing ?
>After all there are no performance problems at that point..

   ...and just how do you tell the exec code that a page fault that occured
while it was accessing the image header was "fatal"? The only mechanism we
have for this is signals, and that doesn't work when you're executing in the
kernel like this.

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project