linux-kernel - Re: [PATCH v6 7/8] dynamic_debug: add asm-generic implementation for DYNAMIC_DEBUG_RELATIVE

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Date:   Tue, 25 Jun 2019 08:35:06 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jason Baron <jbaron@...mai.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 7/8] dynamic_debug: add asm-generic implementation for
 DYNAMIC_DEBUG_RELATIVE_POINTERS

On 24/06/2019 23.53, Nick Desaulniers wrote:
> On Thu, Jun 20, 2019 at 1:46 PM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
>>
>> I've pushed them to https://github.com/Villemoes/linux/tree/dyndebug_v6
>> . They rebase pretty cleanly to just about anything you might prefer
>> testing on. Enabling it for arm64 or ppc64 is a trivial two-liner
>> similar to the x86 patch (and similar to the previous patches for those
>> arches). Thanks for volunteering to test this :)
> 
> Compile tested x86_64 allyesconfig
> boot tested x86_64 defconfig+CONFIG_DYNAMIC_DEBUG
> 
> (just curious why the Kconfig changes for arm64 or ppc64 aren't
> included in this set?)

Partly because I can't boot test those and this has proven much more
delicate than I thought, partly because none of the maintainers for
those arches have weighed in. So I'd rather have the bare minimal land,
then send specific individual patches for arm64 and ppc64.

>>> Anything I should test at runtime besides a boot
>>> test?
>>
>> Well, apart from booting, I've mostly just tested that the debugfs
>> control file is identical before and after enabling relative pointers,
> 
> mainline x86_64 defconfig+CONFIG_DYNAMIC_DEBUG
> $ cat /dfs/dynamic_debug/control  | wc -l
> 2488
> 
> 
> mainline x86_64 defconfig+CONFIG_DYNAMIC_DEBUG+this patch series
> $ cat /dfs/dynamic_debug/control  | wc -l
> 2486
> 
> (seems like maybe 2 are missing?  Let me try to collect a diff. Maybe
> 2 were removed in this series?)

Hm, no pr_debugs should have been added or removed. Perhaps you have a
slightly different set of modules loaded? Otherwise there's something
odd going on, and a diff would be really nice. It's possible that the
order of the lines are different, so you may have to sort them to get a
meaningful diff. (A diff is nice extra sanity check even if the line
count matches, of course).

>> and that enabling/disabling various pr_debug()s by writing to the
>> control file takes effect. I should only be changing the format for
> 
> Can you suggest one that's easy to test?

The ones in lib/kobject.c are triggered fairly often I think.

Thanks,
Rasmus