From 05062d96a23ec0959ee5ea969f40813170c73c0e Mon Sep 17 00:00:00 2001
From: Peter Chubb <peterc@gelato.unsw.edu.au>
Date: Wed, 8 Jun 2005 15:50:20 -0700
Subject: [PATCH] [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>
---
arch/ia64/kernel/ptrace.c | 6 ++++++
arch/ia64/kernel/traps.c | 11 ++++++++++-
include/asm-ia64/processor.h | 10 ++++++++--
3 files changed, 24 insertions(+), 3 deletions(-)
diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c
index 08c8a5eb25ab..575a8f657b31 100644
--- a/arch/ia64/kernel/ptrace.c
+++ b/arch/ia64/kernel/ptrace.c
@@ -635,11 +635,17 @@ ia64_flush_fph (struct task_struct *task)
{
struct ia64_psr *psr = ia64_psr(ia64_task_regs(task));
+ /*
+ * Prevent migrating this task while
+ * we're fiddling with the FPU state
+ */
+ preempt_disable();
if (ia64_is_local_fpu_owner(task) && psr->mfh) {
psr->mfh = 0;
task->thread.flags |= IA64_THREAD_FPH_VALID;
ia64_save_fpu(&task->thread.fph[0]);
}
+ preempt_enable();
}
/*
diff --git a/arch/ia64/kernel/traps.c b/arch/ia64/kernel/traps.c
index 9bad6652d531..1861173bd4f6 100644
--- a/arch/ia64/kernel/traps.c
+++ b/arch/ia64/kernel/traps.c
@@ -220,13 +220,21 @@ disabled_fph_fault (struct pt_regs *regs)
/* first, grant user-level access to fph partition: */
psr->dfh = 0;
+
+ /*
+ * Make sure that no other task gets in on this processor
+ * while we're claiming the FPU
+ */
+ preempt_disable();
#ifndef CONFIG_SMP
{
struct task_struct *fpu_owner
= (struct task_struct *)ia64_get_kr(IA64_KR_FPU_OWNER);
- if (ia64_is_local_fpu_owner(current))
+ if (ia64_is_local_fpu_owner(current)) {
+ preempt_enable_no_resched();
return;
+ }
if (fpu_owner)
ia64_flush_fph(fpu_owner);
@@ -244,6 +252,7 @@ disabled_fph_fault (struct pt_regs *regs)
*/
psr->mfh = 1;
}
+ preempt_enable_no_resched();
}
static inline int
diff --git a/include/asm-ia64/processor.h b/include/asm-ia64/processor.h
index 9e1ba8b7fb68..91bbd1f22461 100644
--- a/include/asm-ia64/processor.h
+++ b/include/asm-ia64/processor.h
@@ -403,7 +403,10 @@ extern void ia64_setreg_unknown_kr (void);
* task_struct at this point.
*/
-/* Return TRUE if task T owns the fph partition of the CPU we're running on. */
+/*
+ * Return TRUE if task T owns the fph partition of the CPU we're running on.
+ * Must be called from code that has preemption disabled.
+ */
#define ia64_is_local_fpu_owner(t) \
({ \
struct task_struct *__ia64_islfo_task = (t); \
@@ -411,7 +414,10 @@ extern void ia64_setreg_unknown_kr (void);
&& __ia64_islfo_task == (struct task_struct *) ia64_get_kr(IA64_KR_FPU_OWNER)); \
})
-/* Mark task T as owning the fph partition of the CPU we're running on. */
+/*
+ * Mark task T as owning the fph partition of the CPU we're running on.
+ * Must be called from code that has preemption disabled.
+ */
#define ia64_set_local_fpu_owner(t) do { \
struct task_struct *__ia64_slfo_task = (t); \
__ia64_slfo_task->thread.last_fph_cpu = smp_processor_id(); \