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SubjectRe: [PATCH]: linux-2.6.21-uc0 (MMU-less updates)
Date
On Thu 3 May 2007 09:30, Greg Ungerer pondered:
> Robin Getz wrote:
> > On Thu 3 May 2007 07:03, Greg Ungerer pondered:
> >> Robin Getz wrote:
> >>> On Wed 2 May 2007 07:32, Greg Ungerer pondered:
> >>>> Robin Getz wrote:
> >>>>> I was trying to understand why we don't want to do the same checking
> >>>>> on noMMU?
> >>>>
> >>>> The problem is on systems that have RAM mapped at high physical
> >>>> addresses. TASK_SIZE may well be a numerically smaller number
> >>>> than the address range that RAM sits in. So this test fails when
> >>>> it shouldn't.

Put the patch back, since I added some new cc'

> diff -Naur linux-2.6.21/fs/namei.c linux-2.6.21-uc0/fs/namei.c
> --- linux-2.6.21/fs/namei.c 2007-05-01 17:12:53.000000000 +1000
> +++ linux-2.6.21-uc0/fs/namei.c 2007-05-01 17:16:18.000000000 +1000
> @@ -120,12 +120,14 @@
> int retval;
> unsigned long len = PATH_MAX;
>
> +#ifdef CONFIG_MMU
> if (!segment_eq(get_fs(), KERNEL_DS)) {
> if ((unsigned long) filename >= TASK_SIZE)
> return -EFAULT;
> if (TASK_SIZE - (unsigned long) filename < PATH_MAX)
> len = TASK_SIZE - (unsigned long) filename;
> }
> +#endif
>
> retval = strncpy_from_user(page, filename, len);
> if (retval > 0) {


> >>>
> >>> So, then this is a problem only on one or two architectures, not all
> >>> noMMU platforms?
> >>
> >> Its not an architecture problem. It can effect any board that
> >> has RAM mapped at a large numerical addresses (larger than TASK_SIZE).
> >> So it can effect any non-MMU platform.
> >
> > Depending on how TASK_SIZE is defined - it looks like everyone else
> > forces it to end of memory, except 68k[nommu].
> >
> > asm-arm/memory.h:#define TASK_SIZE (CONFIG_DRAM_SIZE)
> > asm-blackfin/processor.h:#define TASK_SIZE (memory_end)
> > asm-frv/mem-layout.h:#define TASK_SIZE
> > __UL(0xFFFFFFFFUL)
> >
> > asm-m68k/processor.h:#define TASK_SIZE (0xF0000000UL)
> > asm-m68k/processor.h:#define TASK_SIZE (0x0E000000)
> > asm-m68k/processor.h:#define TASK_SIZE (0x0E000000UL)
> > asm-m68knommu/processor.h:#define TASK_SIZE (0xF0000000UL)
>
> Probably too:
>
> asm-sh/processor.h:#define TASK_SIZE 0x7c000000UL
>
> which has some parts with MMU.
>
> There have been others out of tree that have it like this to.
>
> > I'm happy to learn we are doing something wrong, but I think that we just
> > copied the arm/frv setup.
>
> That is one way to handle it. Have you followed all the other
> uses of TASK_SIZE and verified it is not a problem?

No, I assumed that Russell/David were smarter than we were, and that doing so
would not be a problem :)

Not looking at ./arch or ./include TASK_SIZE looks like it is only used in

fs/hugetlbfs/inode.c
fs/binfmt_elf.c
fs/namespace.c
fs/binfmt_aout.c
fs/namei.c
kernel/kexec.c
mm/mremap.c
mm/mempolicy.c
mm/memory.c
mm/nommu.c
mm/mmap.c

I poked through some, and from first glance, it mostly looked OK with setting
TASK_SIZE to CONFIG_DRAM_SIZE or memory_end.

-Robin
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