linux-kernel - Re: [PATCH] generic ipi function calls: wait on alloc failure fallback

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Message-ID: <20080718221922.GC31073@elte.hu>
Date:	Sat, 19 Jul 2008 00:19:22 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] generic ipi function calls: wait on alloc failure
	fallback


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

>> does this explain the xen64 weirdnesses you've been seeing?
>>   
>
> No, but I haven't seen it lately.  I think the other RCU fixes may 
> have helped.  But it's all a bit of a worry: I didn't have a good 
> theory about what was going wrong, the RCU patches didn't look like 
> they'd fix the symptoms I was seeing.
>
> I've seen it with 32 and 64-bit Xen, but there's nothing about the 
> problem which makes me think it's really Xen specific.  If it were, 
> I'd expect to see failures all over the place, rather than in just in 
> this one specific place.
>
> I'm concerned there's a lurking bug, particularly if it's a generic 
> race or something that happens to be triggered when running under Xen 
> because of the timing changes.  I've tried reproducing it in a hvm Xen 
> domain (so it's running the normal x86 kernel fully virtualized, but 
> with the Xen scheduler, etc).  I didn't see a problem, but it isn't a 
> very convincing test one way or the other.

ok. I doubt there's much we can do at this stage - the code looks fine. 
If it's some recently added core kernel problem sooner or later some 
workload or hw will come about that shows it in a more debuggable 
manner.

	Ingo
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