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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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