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Date: Mon, 24 Sep 2012 20:29:00 +0800
From: Fengguang Wu <fengguang.wu@intel.com>
To: Borislav Petkov <bp@amd64.org>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Jan Kara <jack@suse.cz>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <jweiner@redhat.com>,
        Conny Seidel <conny.seidel@amd.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: divide error: bdi_dirty_limit+0x5a/0x9e
Message-ID: <20120924122900.GA28627@localhost>
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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