Re: 4.0.0-rc4: panic in free_block

[David Miller <davem@davemloft.net>]

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sun, 22 Mar 2015 16:49:51 -0700

> On Sun, Mar 22, 2015 at 3:23 PM, David Miller <davem@davemloft.net> wrote:
>>
>> Yes, using VIS how we do is alright, and in fact I did an audit of
>> this about 1 year ago.  This is another one of those "if this is
>> wrong, so much stuff would break"
> 
> Maybe. But it does seem like Bob Picco has narrowed it down to memmove().
> 
> It also bothers me enormously - and perhaps unreasonably - how that
> memcpy code has memory barriers in it. I can see _zero_ reason for a
> memory barrier inside a memcpy, unless the memcpy does something that
> isn't valid to begin with. Are the VIS operatiosn perhaps using some
> kind of non-temporal form that doesn't follow the TSO rules? Kind of
> like the "movnt" that Intel has?

The special cache line clearing stores (the ASI_BLK_INIT_QUAD_LDD_P
stuff) do not adhere to the memory model.

I had elided the memory barriers originally, but it caused memory
corruption.

So yes, this is similar to the 'movnt' situation.

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