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

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Date:	Fri, 3 Feb 2012 05:29:10 -0500
From:	Mike Frysinger <vapier@...too.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>,
	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
Subject: Re: [RESEND][PATCH] Mark thread stack correctly in proc/<pid>/maps

On Friday 03 February 2012 03:01:35 KOSAKI Motohiro wrote:
> > Right now MAP_STACK does not mean anything since it is ignored. The
> > intention of this behaviour change is to make MAP_STACK mean that the
> > map is going to be used as a stack and hence, set it up like a stack
> > ought to be. I could not really think of a valid case for fixed size
> > stacks; it looks like a limitation in the pthread implementation in
> > glibc rather than a feature. So this patch will actually result in
> > uniform behaviour across threads when it comes to stacks.
> > 
> > This does change vm accounting since thread stacks were earlier
> > accounted as anon memory.
> 
> 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.

does it though ?  glibc doesn't keep track of the unused address space ... 
that's what the kernel is for.  pthread_attr_setstacksize explicitly operates 
on the *minimum* stack size, not the *exact* size.

where exactly do you think userland would break ?

http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_attr_setstacksize.html
-mike

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