linux-kernel - Re: [PATCH x86/mm] x86_64 save_i387

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Message-ID: <5212.1200117118@turing-police.cc.vt.edu>
Date:	Sat, 12 Jan 2008 00:51:58 -0500
From:	Valdis.Kletnieks@...edu
To:	Roland McGrath <roland@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH x86/mm] x86_64 save_i387_ia32 snafu

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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