linux-kernel - Re: Cross Memory Attach v3

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Date:	Sun, 4 Dec 2011 15:19:44 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Christopher Yeoh <cyeoh@....ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-man@...r.kernel.org,
	linux-arch@...r.kernel.org,
	"Linux/m68k" <linux-m68k@...r.kernel.org>,
	Debian m68k <debian-68k@...ts.debian.org>
Subject: Re: Cross Memory Attach v3

Hi Christopher,

On Mon, Nov 21, 2011 at 01:13, Christopher Yeoh <cyeoh@....ibm.com> wrote:
> On Sun, 20 Nov 2011 11:16:17 +0100
> Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> On Mon, Jul 18, 2011 at 17:05, Christopher Yeoh <cyeoh@....ibm.com>
>> wrote:
>> > For arch maintainers there are some simple tests to be able to
>> > quickly verify that the syscalls are working correctly here:
>>
>> I'm wiring up these new syscalls on m68k.
>>
>> On m68k (ARAnyM), the first and third test succeed. The second one
>> fails, though:
>>
>> # Setting up target with num iovecs 10, test buffer size 100000
>> Target process is setup
>> Run the following to test:
>> ./t_process_vm_readv_iovec 1574 10 0x800030b0 89 0x80003110 38302
>> 0x8000c6b8 22423 0x80011e58 18864 0x80016810 583 0x80016a60 8054
>> 0x800189e0 3417 0x80019740 368 0x800198b8 897 0x80019c40 7003
>>
>> and in the other window:
>>
>> # ./t_process_vm_readv_iovec 1574 10 0x800030b0 89 0x80003110 38302
>> 0x8000c6b8 22423 0x80011e58 18864 0x80016810 583 0x80016a60 8054
>> 0x800189e0 3417 0x80019740 368 0x800198b8 897 0x80019c40 7003
>> copy_from_process failed: Invalid argument
>
> That should say process_vm_readv instead of copy_from_process. The
> error message is fixed in the just updated test.
>
>> error code: 29
>> #
>>
>> Any suggestions?
>
> Given that the first and third tests succeed, I think the problem is
> with the iovec parameters. The -EINVAL is most likely coming from
> rw_copy_check_uvector. Any chance that something bad is
> happening to lvec/liovcnt or rvec/riovcnt in the wireup?
>
> The iovecs are checked in process_vm_rw before the core of the
> process_vm_readv/writev code is called so should be easy to confirm if
> this is the problem.
>
> The other couple of places where it could possibly come from is that
> for some reason the flags parameter ends up being non zero or when
> looking up the task the mm is NULL. But given that the first and second
> tests succeed I think its unlikely that either of these is the cause.

It turned out the flags parameter was non-zero, due to syscall() only supporting
up to 5 parameters in the glibc I was using for testing.

I checked the eglibc sources (2.11.1-0ubuntu7.8), and it's still not
fixed there,
although I could find a fix for a similar issue in klibc
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=334917).

When forcing flags to zero, it works ;-)
So sorry for bothering you.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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