Date: Tue, 4 Aug 2009 23:34:17 -0700 From: Navdeep Parhar <nparhar@gmail.com> To: "Bjoern A. Zeeb" <bz@FreeBSD.org> Cc: freebsd-current@freebsd.org, Navdeep Parhar <np@FreeBSD.org> Subject: Re: reproducible panic in netisr Message-ID: <20090805063417.GA10969@doormat.home> In-Reply-To: <20090805054115.O93661@maildrop.int.zabbadoz.net> References: <20090804225806.GA54680@hub.freebsd.org> <20090805054115.O93661@maildrop.int.zabbadoz.net>
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On Wed, Aug 05, 2009 at 05:43:17AM +0000, Bjoern A. Zeeb wrote:
> On Tue, 4 Aug 2009, Navdeep Parhar wrote:
>
> Hi,
>
> >This occurs on today's HEAD + some unrelated patches. That makes it
> >8.0BETA2+ code. I haven't tried older builds.
>
> We have finally been able to reproduce this ourselves yesterday and
Well, it happens every single time on all of my amd64 machines.
After I'd already sent my email I noticed that the netisr mutex has
an odd address (pun intended :-))
m=0xffffffff8144d867
It's a bit unusual for the mutex struct to start at a completely
unaligned address. I hope things are better on sparc64 etc., not
everyone is as forgiving as amd64.
The mutex led me to some DPCPU stuff that I didn't quite get.
(kgdb) p/x dpcpu_off
$2 = {0x8407d7, 0xffffff807f4037d7, 0x0 <repeats 30 times>}
(kgdb) p dpcpu
$3 = (void *) 0xffffff8000010000
(kgdb) p &__start_set_pcpu
$4 = (uintptr_t **) 0xffffffff80c0c829
(kgdb) p/x 0xffffff8000010000 - 0xffffffff80c0c829
$5 = 0xffffff807f4037d7
It's not clear why we prefer to store offsets from DPCPU_START,
instead of the base address of the dpcpu area directly. On amd64,
the dpcpu area for cpu 0 is above kernbase (immediately after
kernbase + thread0's stack). For the other CPUs it's below
kernbase. This makes the pointer arithmetic that calculates offsets
more "interesting."
Why have a dpcpu_off[] instead of a dpcpu_base[]?
> I might have a patch that I need to discuss with the relevant parties
> first, to confirm that it's correct before circulating another bug as
> patchh, as well as confirm some things with objdump.
I should be able to test it. As I mentioned I get a page fault
everytime I run NPtcp -h localhost.
Regards,
Navdeep
>
> /bz
>
> --
> Bjoern A. Zeeb The greatest risk is not taking one.
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