linux-kernel - Re: [RESEND][PATCH] Mark thread stack correctly in proc/<pid>/maps

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Message-ID: <CAAHN_R0N=3J4=VqvDsGB=_2Ln9yKBjOevW2=_UAMBK1pGepqvA@mail.gmail.com>
Date:	Wed, 8 Feb 2012 09:30:36 +0530
From:	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Jamie Lokier <jamie@...reable.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	linux-man@...r.kernel.org, Mike Frysinger <vapier@...too.org>
Subject: Re: [RESEND][PATCH] Mark thread stack correctly in proc/<pid>/maps

On Sat, Feb 4, 2012 at 12:04 AM, Siddhesh Poyarekar
<siddhesh.poyarekar@...il.com> wrote:
> On Fri, Feb 3, 2012 at 1:31 PM, KOSAKI Motohiro
> <kosaki.motohiro@...il.com> wrote:
>> The fact is, now process stack and pthread stack clearly behave
>> different dance. libc don't expect pthread stack grow automatically.
>> So, your patch will break userland. Just only change display thing.
<snip>
> I have also dropped an email on the libc-alpha list here to solicit
> comments from libc maintainers on this:
>
> http://sourceware.org/ml/libc-alpha/2012-02/msg00036.html
>

Kosaki-san, your suggestion of adding an extra flag seems like the
right way to go about this based on the discussion on libc-alpha,
specifically, your point about pthread_getattr_np() -- it may not be a
standard, but it's a breakage anyway. However, looking at the vm_flags
options in mm.h, it looks like the entire 32-bit space has been
exhausted for the flag value. The vm_flags is an unsigned long, so it
ought to take 8 bytes on a 64-bit system, but 32-bit systems will be
left behind.

So there are two options for this:

1) make vm_flags 64-bit for all arches. This will cause ABI breakage
on 32-bit systems, so any external drivers will have to be rebuilt
2) Implement this patch for 64-bit only by defining the new flag only
for 64-bit. 32-bit systems behave as is

Which of these would be better? I prefer the latter because it looks
like the path of least breakage.

-- 
Siddhesh Poyarekar
http://siddhesh.in
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