From owner-freebsd-hackers  Mon Nov  2 19:47:46 1998
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To: "Larry S. Lile" <lile@stdio.com>
cc: hackers@FreeBSD.ORG
Subject: Re: "panic: free: multiple frees" VM bug? (long) 
In-reply-to: Your message of "Mon, 02 Nov 1998 21:35:37 EST."
             <Pine.BSF.3.96.981102212308.17694B-100000@heathers.stdio.com> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Mon, 02 Nov 1998 19:49:04 -0800
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>I am working on a token ring driver and I cannot seem to find
>out why this is happening.  I contigmalloc buffers for tranmsitting
>frames and then free them later when they have been transmitted.
>I have to use contigmalloc in order to get buffers below the
>16M mark for dma.
>
>Anyone see what is wrong? Should I not do this? Or have I
>stumbled over a vm bug?
>
>It looks like a vm bug to me, but I have been wrong before.

   contigmalloc() isn't just a special version of malloc() that allocates
contiguous pages. It's actually a special allocator that has nothing to
do with malloc() and it is thus entirely incorrect to call free() with
a pointer to something that was allocated by contigmalloc(). The proper
way to free stuff that was allocated with contigmalloc() is with kmem_free().
   contigmalloc() is poorly named and should never have been brought into
the kernel that way.

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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