linux-kernel - Re: 4.0.0-rc4: panic in free

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Message-ID: <CA+55aFwEq09vwnxPEYr67O7nuOEN9_n-uJKX11qSbuBNGJVghg@mail.gmail.com>
Date:	Sun, 22 Mar 2015 12:47:08 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	David Ahern <david.ahern@...cle.com>, sparclinux@...r.kernel.org,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: 4.0.0-rc4: panic in free_block

On Sun, Mar 22, 2015 at 10:36 AM, David Miller <davem@...emloft.net> wrote:
>
> And they end up using that byte-at-a-time code, since SLAB and SLUB
> do mmemove() calls of the form:
>
>         memmove(X + N, X, LEN);

Actually, the common case in slab is overlapping but of the form

     memmove(p, p+x, len);

which goes to memcpy. It's basically re-compacting the array at the beginning.

Which was why I was asking how sure you are that memcpy *always*
copies from low to high.

I don't even know which version of memcpy ends up being used on M7.
Some of them do things like use VIS. I can follow some regular sparc
asm, there's no way I'm even *looking* at that. Is it really ok to use
VIS registers in random contexts?

                           Linus
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