fpu, preempt, ptrace

[Atsushi Nemoto <anemo@mba.ocn.ne.jp>]

Here is a (revised) patch to fix some preempt issues around fpu and ptrace.

For now, get_fpu_regs() is used in ptrace code only and the condition
'tsk == current' should always be false.  So we can just remove
_save_fp() call instead of disabling preemption.

diff -ur linux-mips/arch/mips/kernel/ptrace.c linux/arch/mips/kernel/ptrace.c
--- linux-mips/arch/mips/kernel/ptrace.c        2005-04-18 11:42:47.000000000 
+0900
+++ linux/arch/mips/kernel/ptrace.c     2005-05-10 11:41:35.000000000 +0900
@@ -169,10 +169,12 @@
                        if (!cpu_has_fpu)
                                break;
 
+                       preempt_disable();
                        flags = read_c0_status();
                        __enable_fpu();
                        __asm__ __volatile__("cfc1\t%0,$0": "=r" (tmp));
                        write_c0_status(flags);
+                       preempt_enable();
                        break;
                }
                default:
diff -ur linux-mips/arch/mips/kernel/ptrace32.c 
linux/arch/mips/kernel/ptrace32.c
--- linux-mips/arch/mips/kernel/ptrace32.c      2005-04-18 11:42:47.000000000 
+0900
+++ linux/arch/mips/kernel/ptrace32.c   2005-05-10 11:38:51.000000000 +0900
@@ -155,10 +155,12 @@
                        if (!cpu_has_fpu)
                                break;
 
+                       preempt_disable();
                        flags = read_c0_status();
                        __enable_fpu();
                        __asm__ __volatile__("cfc1\t%0,$0": "=r" (tmp));
                        write_c0_status(flags);
+                       preempt_enable();
                        break;
                }
                default:
diff -ur linux-mips/include/asm-mips/fpu.h linux/include/asm-mips/fpu.h
--- linux-mips/include/asm-mips/fpu.h   2005-05-10 10:21:31.000000000 +0900
+++ linux/include/asm-mips/fpu.h        2005-05-10 11:38:38.000000000 +0900
@@ -132,8 +132,10 @@
 static inline fpureg_t *get_fpu_regs(struct task_struct *tsk)
 {
        if (cpu_has_fpu) {
+               preempt_disable();
                if ((tsk == current) && __is_fpu_owner()) 
                        _save_fp(current);
+               preempt_enable();
                return tsk->thread.fpu.hard.fpr;
        }
 
---
Atsushi Nemoto