mm: Prepare decoupling the page fault disabling logic

Add a pagefault_disabled variable to task_struct to allow decoupling
the pagefault-disabled logic from the preempt count.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 29 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 829d43735402..52e3f6502b50 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3436,6 +3436,35 @@ unlock:
 	return 0;
 }
 
+void pagefault_disable(void)
+{
+	inc_preempt_count();
+	current->pagefault_disabled++;
+	/*
+	 * make sure to have issued the store before a pagefault
+	 * can hit.
+	 */
+	barrier();
+}
+EXPORT_SYMBOL_GPL(pagefault_disable);
+
+void pagefault_enable(void)
+{
+	/*
+	 * make sure to issue those last loads/stores before enabling
+	 * the pagefault handler again.
+	 */
+	barrier();
+	current->pagefault_disabled--;
+	dec_preempt_count();
+	/*
+	 * make sure we do..
+	 */
+	barrier();
+	preempt_check_resched();
+}
+EXPORT_SYMBOL_GPL(pagefault_enable);
+
 /*
  * By the time we get here, we already hold the mm semaphore
  */