[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>
diff --git a/arch/ia64/kernel/traps.c b/arch/ia64/kernel/traps.c
index 9bad665..1861173 100644
--- a/arch/ia64/kernel/traps.c
+++ b/arch/ia64/kernel/traps.c
@@ -220,13 +220,21 @@
/* 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 @@
*/
psr->mfh = 1;
}
+ preempt_enable_no_resched();
}
static inline int