Re: divide error: bdi_dirty_limit+0x5a/0x9e

[Borislav Petkov]

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?

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