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

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Date:	Mon, 23 Mar 2015 16:08:42 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	john@...ffel.org
Cc:	david.ahern@...cle.com, torvalds@...ux-foundation.org,
	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: "John Stoffel" <john@...ffel.org>
Date: Mon, 23 Mar 2015 15:56:02 -0400

>>>>>> "David" == David Miller <davem@...emloft.net> writes:
> 
> David> From: "John Stoffel" <john@...ffel.org>
> David> Date: Mon, 23 Mar 2015 12:51:03 -0400
> 
>>> Would it make sense to have some memmove()/memcopy() tests on bootup
>>> to catch problems like this?  I know this is a strange case, and
>>> probably not too common, but how hard would it be to wire up tests
>>> that go through 1 to 128 byte memmove() on bootup to make sure things
>>> work properly?
>>> 
>>> This seems like one of those critical, but subtle things to be
>>> checked.  And doing it only on bootup wouldn't slow anything down and
>>> would (ideally) automatically get us coverage when people add new
>>> archs or update the code.
> 
> David> One of two things is already happening.
> 
> David> There have been assembler memcpy/memset development test harnesses
> David> around that most arch developers are using, and those test things
> David> rather extensively.
> 
> David> Also, the memcpy/memset routines on sparc in particular are completely
> David> shared with glibc, we use the same exact code in both trees.  So it's
> David> getting tested there too.
> 
> Thats' good to know.   I wasn't sure.
> 
> David> memmove() is just not handled this way.
> 
> Bummers.  So why isn't this covered by the glibc tests too?

Because the kernel's memmove() is different from the one we use in glibc
on sparc.  In fact, we use the generic C version in glibc which expands
to forward and backward word copies.
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