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Re: FPU emul and segmentation fault bug

To: Jun Sun <jsun@mvista.com>
Subject: Re: FPU emul and segmentation fault bug
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Mon, 25 Feb 2002 04:11:54 +0100
Cc: linux-mips@oss.sgi.com
In-reply-to: <3C76F53D.2C893BC7@mvista.com>; from jsun@mvista.com on Fri, Feb 22, 2002 at 05:49:49PM -0800
References: <3C76F53D.2C893BC7@mvista.com>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Fri, Feb 22, 2002 at 05:49:49PM -0800, Jun Sun wrote:

> I remember a while back we had a problem with FPU emulation code which causes
> a segmentation fault.  (Perhaps another symptom is bus error, but I am not
> 100% sure).
> 
> Apparently this problem is fixed in the recent kernel.  However, it shows up
> again in SMP mode.
> 
> Does anybody remember details of the problem and the fix?  I am afraid maybe
> something we did there is not SMP safe.

That's most probably a SMP cache invalidation bug.  What happens is that
remote CPUs try to invalidate the same address range as a local CPU as
well without any consideration that the active context of the remote
CPU might be different from the local one.  In combination with another
bug this may actually crash the whole system.

  Ralf

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