From: Peter Chubb <peterc@gelato.unsw.edu.au>
Date: Wed, 8 Jun 2005 22:50:20 +0000 (-0700)
Subject: [PATCH] ia64: fix floating-point preemption problem
X-Git-Tag: v2.6.12~56
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=05062d96a23ec0959ee5ea969f40813170c73c0e;p=pandora-kernel.git

[PATCH] ia64: fix floating-point preemption problem

There've been reports of problems with CONFIG_PREEMPT=y and the high
floating point partition.  This is caused by the possibility of preemption
and rescheduling on a different processor while saving or restioirng the
high partition.

The only places where the FPU state is touched are in ptrace, in
switch_to(), and where handling a floating-point exception.  In switch_to()
preemption is off.  So it's only in trap.c and ptrace.c that we need to
prevent preemption.

Here is a patch that adds commentary to make the conditions clear, and adds
appropriate preempt_{en,dis}able() calls to make it so.  In trap.c I use
preempt_enable_no_resched(), as we're about to return to user space where
the preemption flag will be checked anyway.

Signed-off-by: Peter Chubb <peterc@gelato.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

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