linux-kernel - Re: stack overflow on Sparc64

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Message-ID: <Pine.LNX.4.64.0806201717190.14221@engineering.redhat.com>
Date:	Fri, 20 Jun 2008 17:26:35 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	David Miller <davem@...emloft.net>
cc:	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	agk@...hat.com
Subject: Re: stack overflow on Sparc64

On Fri, 20 Jun 2008, David Miller wrote:

> 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.

I meant if some fancy networking options can eat those 19 frames that I 
saved and crash again? I use the computer as a workstation, it doesn't 
have high network load and it doesn't use any features except basic 
TCP/IP.

>> 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.

If you think that process context+network processing+hardirqs can fit into 
75 nested functions... I really have no idea how much the networking 
takes, given the amount of protocols and features and inability to test 
them all in one lab, it looks very scary.

Mikulas
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