[PATCH] PPC/PPC64: Fix FP state corruption on UP

Unfortunately the patch Ben sent last week to fix a bug in the saving and
restoring of floating-point and altivec context across signal handlers
introduced another bug, which tends to corrupt the FP and altivec contexts
of other tasks.  This patch fixes the problem for both ppc32 and ppc64. 
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc/kernel/signal.c

@@ -290,7 +290,7 @@ restore_user_regs(struct pt_regs *regs, struct mcontext __user *sr, int sig)
 
 	/* force the process to reload the FP registers from
 	   current->thread when it next does FP instructions */
-	regs->msr &= ~MSR_FP;
+	regs->msr &= ~(MSR_FP | MSR_FE0 | MSR_FE1);
 	if (__copy_from_user(current->thread.fpr, &sr->mc_fregs,
 			     sizeof(sr->mc_fregs)))
 		return 1;
@@ -330,9 +330,14 @@ restore_user_regs(struct pt_regs *regs, struct mcontext __user *sr, int sig)
 #endif /* CONFIG_SPE */
 
 #ifndef CONFIG_SMP
-	last_task_used_math = NULL;
-	last_task_used_altivec = NULL;
-	last_task_used_spe = NULL;
+	preempt_disable();
+	if (last_task_used_math == current)
+		last_task_used_math = NULL;
+	if (last_task_used_altivec == current)
+		last_task_used_altivec = NULL;
+	if (last_task_used_spe == current)
+		last_task_used_spe = NULL;
+	preempt_enable();
 #endif
 	return 0;
 }

arch/ppc64/kernel/signal.c

@@ -224,8 +224,12 @@ static long restore_sigcontext(struct pt_regs *regs, sigset_t *set, int sig,
 #endif /* CONFIG_ALTIVEC */
 
 #ifndef CONFIG_SMP
-	last_task_used_math = NULL;
-	last_task_used_altivec = NULL;
+	preempt_disable();
+	if (last_task_used_math == current)
+		last_task_used_math = NULL;
+	if (last_task_used_altivec == current)
+		last_task_used_altivec = NULL;
+	preempt_enable();
 #endif
 	/* Force reload of FP/VEC */
 	regs->msr &= ~(MSR_FP | MSR_FE0 | MSR_FE1 | MSR_VEC);

arch/ppc64/kernel/signal32.c

@@ -235,8 +235,12 @@ static long restore_user_regs(struct pt_regs *regs,
 #endif /* CONFIG_ALTIVEC */
 
 #ifndef CONFIG_SMP
-	last_task_used_math = NULL;
-	last_task_used_altivec = NULL;
+	preempt_disable();
+	if (last_task_used_math == current)
+		last_task_used_math = NULL;
+	if (last_task_used_altivec == current)
+		last_task_used_altivec = NULL;
+	preempt_enable();
 #endif
 	return 0;
 }