From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Parag Warudkar" Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected Date: Wed, 27 Aug 2008 12:24:08 -0400 Message-ID: References: <20080826183051.GB10925@cs181140183.pp.htv.fi> <20080826205916.GB11734@cs181140183.pp.htv.fi> <20080826232411.GC11734@cs181140183.pp.htv.fi> <20080827092528.780916bd@lxorguk.ukuu.org.uk> <20080827142142.303cdba8@lxorguk.ukuu.org.uk> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to :subject:cc:in-reply-to:mime-version:content-type :content-transfer-encoding:content-disposition:references; bh=VJaK7kWDopuZBbF9g47uepTUlqtfeEQWbc1M3SJTkJQ=; b=TKXxzP8LgHLz5IvAP3BJ3Y8XNoWCmck76yqMBhTtNfwKqsBP3lhitpYqvNJkyYJWf/ J7pgnEj6f0ZuTTXo7NcUYQDjHwLJx/huF+IEo9C7I5QFAZQaCEkTYBf8xF8SPe1VmDRm U04Yaml6ZlY9shZrI2XgSfx+ZaveHtLFWcwqM= In-Reply-To: <20080827142142.303cdba8-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org> Content-Disposition: inline Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Alan Cox Cc: Adrian Bunk , Linus Torvalds , Rusty Russell , "Alan D. Brunelle" , "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , Andrew Morton , Arjan van de Ven , Ingo Molnar , linux-embedded-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Wed, Aug 27, 2008 at 9:21 AM, Alan Cox wrote: >> By your logic though, XFS on x86 should work fine with 4K stacks - >> many will attest that it does not and blows up due to stack issues. >> >> I have first hand experiences of things blowing up with deep call >> chains when using 4K stacks where 8K worked just fine on same >> workload. >> >> So there is definitely some other problem with 4K stacks. > > Nothing of the sort. If it blows up with a 4K stack it will almost > certainly blow up with an 8K stack *eventually* - when a heavy stack usage > coincides with a heavy stack using IRQ handler. > > You won't catch it in simple testing, you won't catch it in trivial > simulation and it'll be incredibly hard to reproduce. Not the kind of bug > you want in a production system really. IRQ stacks make things much more > predictable. I see - so if I end up having a workload on 8k where heavy stack using IRQs and deep kernel call chains come at the same time - even 8K will blow up. So 4K will blow too except that it doesn't require IRQs also to use heavy stack, just XFS is good enough :) It then seems like the IRQs using lot of stack is not so much of a problem in the current kernel as much as deeper call chains and stack usage of normal non-irq path code is. So 8k makes it possible for the deeper call chains of non-irq path to survive since they get better part of the 8K to themselves and IRQs can do with less almost always. At least that's what I can derive from the fact that we do not have lots of reports of 8K stack blowing up. Thanks Parag