linux-kernel - Re: divide error: bdi_dirty

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Message-ID: <20120924122900.GA28627@localhost>
Date:	Mon, 24 Sep 2012 20:29:00 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Borislav Petkov <bp@...64.org>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Jan Kara <jack@...e.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Conny Seidel <conny.seidel@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: divide error: bdi_dirty_limit+0x5a/0x9e

On Mon, Sep 24, 2012 at 02:20:53PM +0200, Borislav Petkov wrote:
> On Mon, Sep 24, 2012 at 07:34:47PM +0800, Fengguang Wu wrote:
> > Will you test such a line? At least the generic do_div() only uses the
> > lower 32bits for division.
> > 
> >         WARN_ON(!(den & 0xffffffff));
> 
> But, but, the asm output says:
> 
>   28:   48 89 c8                mov    %rcx,%rax
>   2b:*  48 f7 f7                div    %rdi     <-- trapping instruction
>   2e:   31 d2                   xor    %edx,%edx
> 
> and this version of DIV does an unsigned division of RDX:RAX by the
> contents of a *64-bit register* ... in our case %rdi.
> 
> Srivatsa's oops  shows the same:
> 
>   28:   48 89 f0                mov    %rsi,%rax
>   2b:*  48 f7 f7                div    %rdi     <-- trapping instruction
>   2e:   41 8b 94 24 74 02 00    mov    0x274(%r12),%edx
> 
> Right?

Right, that's why I said "at least". As for x86, I'm as clueless as you..

Thanks,
Fengguang
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