The __compute_return_epc() uses CFC1 instruction but it might cause a
coprocessor unusable exception since the process can lose its fpu
context by preemption. The coprocessor unusable exception is not
allowed in kernel context.
Here is a patch. Please review. Thank you.
--- linux-mips/arch/mips/kernel/branch.c 2004-08-14 19:55:32.000000000 +0900
+++ linux/arch/mips/kernel/branch.c 2005-04-20 16:33:24.662914765 +0900
@@ -12,6 +12,7 @@
#include <asm/branch.h>
#include <asm/cpu.h>
#include <asm/cpu-features.h>
+#include <asm/fpu.h>
#include <asm/inst.h>
#include <asm/ptrace.h>
#include <asm/uaccess.h>
@@ -163,8 +164,14 @@
case cop1_op:
if (!cpu_has_fpu)
fcr31 = current->thread.fpu.soft.fcr31;
- else
- asm volatile("cfc1\t%0,$31" : "=r" (fcr31));
+ else {
+ preempt_disable();
+ if (is_fpu_owner())
+ asm volatile("cfc1\t%0,$31" : "=r" (fcr31));
+ else
+ fcr31 = current->thread.fpu.hard.fcr31;
+ preempt_enable();
+ }
bit = (insn.i_format.rt >> 2);
bit += (bit != 0);
bit += 23;
---
Atsushi Nemoto
