linux-kernel - Re: [PATCH] - Fix stack overflow for large values of MAX

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Message-ID: <20080620103921.GC32500@elte.hu>
Date:	Fri, 20 Jun 2008 12:39:21 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jack Steiner <steiner@....com>
Cc:	tglx@...utronix.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] - Fix stack overflow for large values of MAX_APICS

* Jack Steiner <steiner@....com> wrote:

> physid_mask_of_physid() causes a huge stack (12k) to be created if the 
> number of APICS is large. Replace physid_mask_of_physid() with a new 
> function that does not create large stacks. This is a problem only on 
> large x86_64 systems.

this indeed fixes the crash i reported here:

   http://lkml.org/lkml/2008/6/19/98

so i've added both this and the MAXAPICS patch to tip/x86/uv, and will 
test it some more. Lets hope it goes all well this time :-)

btw., it would be nice to have an ftrace plugin that prints out the 
worst-case stack footprint and generates an assert if we overflow the 
stack. -rt's kernel/latency_trace.c used to have that feature. That way 
incidents like this would be detected on the spot by -tip's 
auto-testing. The code in question is in kernel/trace/ftrace.c (and 
other nearby code).

	Ingo
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