linux-kernel - Re: [x86] BUG: unable to handle kernel paging request at 00740060

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Message-ID: <20131009143226.GA24911@gmail.com>
Date:	Wed, 9 Oct 2013 16:32:26 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [x86] BUG: unable to handle kernel paging request at 00740060


* Peter Zijlstra <peterz@...radead.org> wrote:

> > This is what we are going to return. But note that -20(%ebp) was not
> > initialized if TIF_NOTIFY_RESUME was already set, "jc .L2" skips .L5
> > above. IOW, in this case we seem to return a random value from stack.
> 
> I think you're quite right, and I can confirm I can reproduce this with
> gcc-4.8.1 and Wu's .config:
>
> [...]
>
> Once I force a x86_64 build using the 'same' config it goes away and 
> generates 'sensible' code again [...]

So this at least opens up the possibility that we can create a not too 
painful quirk and only use the 'asm goto' optimization tricks on 64-bit 
kernels?

Thanks,

	Ingo
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