NetBSD Problem Report #4761

Received: (qmail 12892 invoked from network); 31 Dec 1997 22:47:37 -0000
Date: Wed, 31 Dec 97 17:47:04 EST
From: davide+@cs.cmu.edu
Sender: davide+@piper.nectar.cs.cmu.edu
Reply-To: David_Eckhardt@cs.cmu.edu
To: gnats-bugs@gnats.netbsd.org
Cc: davide+@cs.cmu.edu
Subject: i386 ddb "watch" seems broken
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>Number:         4761
>Category:       kern
>Synopsis:       setting any watchpoint results in a fatal page fault
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Dec 31 14:50:02 +0000 1997
>Closed-Date:    
>Last-Modified:  Mon Feb 28 14:56:22 +0000 2011
>Originator:     David Eckhardt
>Release:        1.2
>Organization:
	Carnegie Mellon University Computer Science Department
>Environment:
	NetBSD 1.1, 1.2, ...?
>Description:
	It seems as though setting any watchpoint with ddb somehow
	destroys the machine state:  I can't get anything but kernel
	page faults.
>How-To-Repeat:
	control-alt-escape, "watch ipstat", "c"
>Fix:
	If this isn't easily fixable, disabling the command would not be
	a bad idea.
>Release-Note:
>Audit-Trail:
Responsible-Changed-From-To: gnats-admin->port-i386-maintainer 
Responsible-Changed-By: fair 
Responsible-Changed-When: Mon Dec 28 09:55:30 PST 1998 
Responsible-Changed-Why:  
This PR is the responsibility of the portmaster, 
not the GNATS database administrator. 
State-Changed-From-To: open->feedback 
State-Changed-By: fair 
State-Changed-When: Thu Jan 17 12:40:16 PST 2002 
State-Changed-Why:  
NetBSD has been through two major releases since this PR was filed; 
does the problem still occurr? 

From: "Perry E. Metzger" <perry@piermont.com>
To: David_Eckhardt@cs.cmu.edu, fvdl@netbsd.org
Cc: gnats-bugs@gnats.netbsd.org, perry@piermont.com
Subject: Re: port-i386/4761
Date: 04 Apr 2003 12:05:32 -0500

 > >Synopsis:       setting any watchpoint results in a fatal page fault
 > >Arrival-Date:   Wed Dec 31 14:50:02 1997

 > >Description:
 >         It seems as though setting any watchpoint with ddb somehow
 >         destroys the machine state:  I can't get anything but kernel
 >         page faults.
 > >How-To-Repeat:
 >        control-alt-escape, "watch ipstat", "c"

 This appears to still be a problem to this day. I just tested it and
 got the stated behavior.

 I'm going to assign the PR to the portmaster.

 Perry
State-Changed-From-To: feedback->open 
State-Changed-By: perry 
State-Changed-When: Fri Apr 4 09:06:08 PST 2003 
State-Changed-Why:  
I just tested the problem -- it still happens, five years later. 


Responsible-Changed-From-To: port-i386-maintainer->fvdl 
Responsible-Changed-By: perry 
Responsible-Changed-When: Fri Apr 4 09:06:08 PST 2003 
Responsible-Changed-Why:  
Frank is the x86 portmaster. 

From: "Charles M. Hannum" <abuse@spamalicious.com>
To: gnats-bugs@gnats.NetBSD.org
Cc:  
Subject: Re: port-i386/4761
Date: Sat, 3 Jul 2004 21:38:54 +0000

 The way watchpoints are handled is sort of doomed.  db_set_watchpoints() uses 
 pmap_protect() to change the page to read-only, and relies on the fault path 
 to restore the permissions later.  However, in many cases UVM does not know 
 about kernel pages, and so the fault fails.
Responsible-Changed-From-To: fvdl->kern-bug-people
Responsible-Changed-By: wiz@NetBSD.org
Responsible-Changed-When: Mon, 28 Feb 2011 14:56:22 +0000
Responsible-Changed-Why:
Reset responsible field for retired developer.


>Unformatted:

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