Re: [PATCH] Gerd Hoffman's move-vsyscall-into-user-address-range patch

[Zachary Amsden <zach@vmware.com>]

Andrew Morton wrote:
> Ingo Molnar <mingo@elte.hu> wrote:
>   
> > * Andrew Morton <akpm@osdl.org> wrote:
> >
> >     
> > > Rusty Russell <rusty@rustcorp.com.au> wrote:
> > >       
> > > > Name: Move vsyscall page out of fixmap into normal vma as per mmap
> > > >         
> > > This causes mysterious hangs when starting init.
> > >
> > > Distro is RH FC1, running SysVinit-2.85-5.
> > >
> > > dmesg, sysrq-T and .config are at
> > > http://www.zip.com.au/~akpm/linux/patches/stuff/log-vmm - nothing leaps
> > > out.
> > >
> > > This is the second time recently when a patch has caused this machine 
> > > to oddly hang in init.  It's possible that there's a bug of some form 
> > > in that version of init that we'll need to know about and take care of 
> > > in some fashion.
> > >       
> > FC1 is like really ancient. I think there was a glibc bug that caused 
> > vsyscall related init hangs like that. To nevertheless let people run 
> > their old stuff there's a vdso=0 boot option in exec-shield.
> >
> >     
>
> Well that patch took a machine from working to non-working.  Pretty serious
> stuff.  We should get to the bottom of the problem so we can assess the
> risk and impact, no?

An easy test for culpability of kernel vs. init would be to back out all 
patches and recompile the kernel with vsyscall moved down by 4 megs.


Index: linux-2.6.17-rc/include/asm-i386/fixmap.h
===================================================================
--- linux-2.6.17-rc.orig/include/asm-i386/fixmap.h	2006-03-19 21:53:29.000000000 -0800
+++ linux-2.6.17-rc/include/asm-i386/fixmap.h	2006-05-19 18:16:00.000000000 -0700
@@ -20,7 +20,7 @@
  * Leave one empty page between vmalloc'ed areas and
  * the start of the fixmap.
  */
-#define __FIXADDR_TOP	0xfffff000
+#define __FIXADDR_TOP	0xffbff000
 
 #ifndef __ASSEMBLY__
 #include <linux/kernel.h>