RE: Kernel Panic with latest patch from git repo

Seems right. Please add directly to the source tree. 

Moshe

-----Original Message-----
From: openmosix-devel-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
[mailto:openmosix-devel-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org] On Behalf Of Ansgar
Esztermann
Sent: Friday, February 24, 2006 2:43 PM
To: Matthieu Pérotin
Cc: openmosix-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: Re: [Openmosix-devel] Kernel Panic with latest patch from git repo

On Tue, Feb 21, 2006 at 09:07:48PM +0100, Matthieu Pérotin wrote:
> When migrating a process from a node A to a node B, the node B crashes 
> on a kernel panic.

I think I've finally figured out what really happens. When I wrote earlier
(to the list) that Node B receives the process at interrupt time, I was
wrong. It only looks that way (and the kernel actually thinks that way)
because the preempt counter overflows. (Note that that counter is kept even
on a kernel with CONFIG_PREEMPT off.)

The counter overflows because there is an unbalanced call to
pte_alloc_map() in mig_do_receive_page(). Now, if CONFIG_HIGHPTE is set,
user space PTEs are allocated in high memory. pte_alloc_map() will
atomically map the PTE so that it can be used; however, that map is never
released.
If CONFIG_HIGHPTE is off, the mapping is #defined away, so the problem does
not surface.

I've created a patch that enables migration even with CONFIG_HIGHPTE on.
I've tested it here, and it seems to work OK, so I'd like to submit it for
inclusion with openMosix.

A.

=======================================================================

diff -ruN linux-2.6-om/hpc/migrecv.c linux-2.6-om-work/hpc/migrecv.c
--- linux-2.6-om/hpc/migrecv.c	2006-02-07 16:51:58.000000000 +0100
+++ linux-2.6-om-work/hpc/migrecv.c	2006-02-24 21:13:35.000000000 +0100
@@ -183,6 +183,7 @@
 		OMBUG("double page at addr %p\n", (void *) addr);
 
 	set_pte(pte, pte_mkdirty(mk_pte(recv_page, vma->vm_page_prot)));
+	pte_unmap(pte);
 	page_dup_rmap(recv_page);
 	inc_mm_counter(mm, file_rss);
 	
--
Ansgar Esztermann
Researcher & Sysadmin
http://www2.thphy.uni-duesseldorf.de/~ansgar



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