[POWERPC] Make soft_enabled irqs preempt safe

Rewrite local_get_flags and local_irq_disable to use r13 explicitly,
to avoid the risk that gcc will split get_paca()->soft_enabled into a
sequence unsafe against preemption.  Similar care in local_irq_restore.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 15 insertions, 5 deletions

diff --git a/include/asm-powerpc/hw_irq.h b/include/asm-powerpc/hw_irq.h
index c4a1ab608f6..fd3f2a20627 100644
--- a/include/asm-powerpc/hw_irq.h
+++ b/include/asm-powerpc/hw_irq.h
@@ -18,15 +18,25 @@ extern void timer_interrupt(struct pt_regs *);
 
 static inline unsigned long local_get_flags(void)
 {
-	return get_paca()->soft_enabled;
+	unsigned long flags;
+
+	__asm__ __volatile__("lbz %0,%1(13)"
+	: "=r" (flags)
+	: "i" (offsetof(struct paca_struct, soft_enabled)));
+
+	return flags;
 }
 
 static inline unsigned long local_irq_disable(void)
 {
-	unsigned long flag = get_paca()->soft_enabled;
-	get_paca()->soft_enabled = 0;
-	barrier();
-	return flag;
+	unsigned long flags, zero;
+
+	__asm__ __volatile__("li %1,0; lbz %0,%2(13); stb %1,%2(13)"
+	: "=r" (flags), "=&r" (zero)
+	: "i" (offsetof(struct paca_struct, soft_enabled))
+	: "memory");
+
+	return flags;
 }
 
 extern void local_irq_restore(unsigned long);