Re: [patch 1/4] powerpc: fix for OProfile callgraph for Power 64 bit user apps

[Michael Ellerman <michael@ellerman.id.au>]

[-- Attachment #1: Type: text/plain, Size: 2002 bytes --]

On Wed, 2008-05-14 at 16:12 -0700, akpm@linux-foundation.org wrote:
> From: Carl Love <cel@us.ibm.com>
> 
> Fix the 64 bit user code backtrace which currently may hang the system.
> 
> Signed-off-by: Carl Love <carll@us.ibm.com>
> Cc: Maynard Johnson <maynardj@us.ibm.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Hi Carl,

I'm a bit confused by this change ..

> diff -puN arch/powerpc/oprofile/backtrace.c~powerpc-fix-for-oprofile-callgraph-for-power-64-bit-user-apps arch/powerpc/oprofile/backtrace.c
> --- a/arch/powerpc/oprofile/backtrace.c~powerpc-fix-for-oprofile-callgraph-for-power-64-bit-user-apps
> +++ a/arch/powerpc/oprofile/backtrace.c
> @@ -53,19 +53,40 @@ static unsigned int user_getsp32(unsigne
>  #ifdef CONFIG_PPC64
>  static unsigned long user_getsp64(unsigned long sp, int is_first)
>  {
> -	unsigned long stack_frame[3];
> +	unsigned long stk_frm_lr;
> +	unsigned long stk_frm_sp;
> +	unsigned long size;
> +
> +	/* Issue the __copy_from_user_inatomic() third argument currently
> +	 * only takes sizes 1, 2, 4 or 8 bytes.  Don't read more then the
> +	 * first 48 bytes of the stack frame.  That is all that is
> +	 * guaranteed to exist.  Reading more may cause the system to hang.

__copy_from_user_inatomic() accepts any value for n, it just has a
special case for 1, 2, 4 and 8 - but it should still work for other
values.

The old code copied 24 bytes from sp, and the new code copies 8 bytes
from sp and 8 bytes from sp + 16 - so I don't see where the 48 bytes
comes in to it?

Also the comment is a little hard to parse, I think you mean "Issue:
the ..", but I read "Issue" as a verb in that sentence. And "Don't read
more then" should be "than".

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 189 bytes --]