linux-kernel - Re: [regression v2.6.38] Re: [PATCH v2] brk: fix min_brk lower bound computation for COMPAT

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Date:	Mon, 28 Mar 2011 16:20:57 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Linux/m68k <linux-m68k@...r.kernel.org>
Subject: Re: [regression v2.6.38] Re: [PATCH v2] brk: fix min_brk lower bound
 computation for COMPAT_BRK

On Sat, 26 Mar 2011, Geert Uytterhoeven wrote:

> >> | RAMDISK: gzip image found at block 0
> >> | VFS: Mounted root (ext2 filesystem) readonly on device 1:0.
> >> | warning: process `update' used the obsolete bdflush system call
> >> | Fix your initscripts?
> >> | init: cannot open inittab
> >> | Kernel panic - not syncing: Attempted to kill init!
> >>
> >> Sorry for not noticing earlier, I usually boot full Debians under ARAnyM,
> >> instead of booting old ramdisks with libc5-based binaries that once were
> >> considered new.
> >
> > Oh well, one has to love the libc5-based binaries indeed.
> 
> Yeah, binaries from 1996 ;-)
> 
> > Is the patch below fixing the issue you are seeing on your Amiga/m68k?
> > Thanks.
> >
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 2ec8eb5..0a02531 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -262,7 +262,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
> >        if (mm->start_brk > PAGE_ALIGN(mm->end_data))
> >                min_brk = mm->start_brk;
> >        else
> > -               min_brk = mm->end_data;
> > +               min_brk = mm->end_code;
> >  #else
> >        min_brk = mm->start_brk;
> >  #endif
> 
> Unfortunately not...
> 
> I added some printk()s:
> 
> mm->start_brk = 0x8000a000, PAGE_ALIGN(mm->end_data = 0x8000a000)
> mm->start_brk = 0x8000a000, PAGE_ALIGN(mm->end_data = 0x8000a000)
> mm->start_brk = 0x8000a000, PAGE_ALIGN(mm->end_data = 0x8000a000)
> mm->start_brk = 0x8000a000, PAGE_ALIGN(mm->end_data = 0x8000a000)
> mm->start_brk = 0x80006000, PAGE_ALIGN(mm->end_data = 0x80004000)
> 
> I.e. just before the failure, "mm->start_brk > PAGE_ALIGN(mm->end_data)"
> became true.

Hmm, I think we'd need some refresh on what the ancient libc5-based 
binaries are actually doing.

Could you please send me strace of this application (restricting it to 
brk()/mmap() calls should be enough).

Thanks,

-- 
Jiri Kosina
SUSE Labs, Novell Inc.
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