To: Roland McGrath <roland@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH x86/mm] x86_64 save_i387_ia32 snafu
In-Reply-To: Your message of "Fri, 11 Jan 2008 13:31:47 PST."
             <20080111213147.EBE0C26F9A9@magilla.localdomain>
From: Valdis.Kletnieks@vt.edu
References: <4786A9CA.2090008@zytor.com> <20080111004422.2B3F926F9A6@magilla.localdomain> <4786BE15.6040604@zytor.com> <20080111024929.37FDB26F9A9@magilla.localdomain> <4786DB3B.8070808@zytor.com> <20080111104357.8364826F9A9@magilla.localdomain> <20080111104932.GA1589@elte.hu>
            <20080111213147.EBE0C26F9A9@magilla.localdomain>
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Date: Sat, 12 Jan 2008 00:51:58 -0500
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On Fri, 11 Jan 2008 13:31:47 PST, Roland McGrath said:
> > thanks, applied. Does this explain the crash/hang problems with 32-bit 
> > apps on 64-bit kernels? What was the exact failure mode?
> 
> It does.  Any 32-bit process trying to run a signal handler when it had
> used the FPU, would clobber "current" with FP bits.  The observed failure
> mode was shortly after this in the signal handler setup code, when it
> crashed due to current->mm being zero (current->pid also being zero, and
> the whole first 512 bytes of the task_struct being garbage).

For what it's worth, this patch fixes a problem I had in 24-rc6-mm1 with
kernel panics when certain X programs exited (Eterm being the biggest cause),
that I had bisected to "somewhere in git-x86.patch"....

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