linux-kernel - Re: stack overflow on Sparc64

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Message-Id: <20080620.133721.95818057.davem@davemloft.net>
Date:	Fri, 20 Jun 2008 13:37:21 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mpatocka@...hat.com
Cc:	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	agk@...hat.com
Subject: Re: stack overflow on Sparc64

From: Mikulas Patocka <mpatocka@...hat.com>
Date: Fri, 20 Jun 2008 16:34:23 -0400 (EDT)

> And what if network softirq happened here? How much stack does it consume?
> 
> The whole overflowed stack trace has 75 functions, I was able to get rid 
> of 9 by avoiding bio_endio recursion and 10 by turning simple functions 
> into inlines. --- so is it enough or not enough for possible networking 
> calls?

It should be OK, because the minimum stack of a (75 - 19) depth call
chain is under 11K and within safe limits I believe.

> Maybe a good thing would be to add a check for stack size to __do_softirq 
> and handing the softirq to ksoftirqd if there's not enough space.

I'd rather it spit out a WARN_ON() message and a backtrace.

Otherwise it will be considered a feature and people won't fix
these deep call chains.
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