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

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Date:	Mon, 23 Mar 2015 15:08:33 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	torvalds@...ux-foundation.org
Cc:	david.ahern@...cle.com, sparclinux@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, bpicco@...oft.net
Subject: Re: 4.0.0-rc4: panic in free_block

From: Linus Torvalds <torvalds@...ux-foundation.org>
Date: Mon, 23 Mar 2015 10:00:02 -0700

> Maybe the code could be something like
> 
>     void *memmove(void *dst, const void *src, size_t n);
>     {
>         // non-overlapping cases
>         if (src + n <= dst)
>             return memcpy(dst, src, n);
>         if (dst + n <= src)
>             return memcpy(dst, src, n);
> 
>         // overlapping, but we know we
>         //  (a) copy upwards
>         //  (b) initialize the result in at most chunks of 64
>         if (dst+64 <= src)
>             return memcpy(dst, src, n);
> 
>         .. do the backwards thing ..
>     }
> 
> (ok, maybe I got it wrong, but you get the idea).
> 
> I *think* gcc should do ok on the above kind of code, and not generate
> wildly different code from your handcoded version.

Sure you could do that in C, but I really want to avoid using memcpy()
if dst and src overlap in any way at all.

Said another way, I don't want to codify that "64" thing.  The next
chip could do 128 byte initializing stores.
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