efi/runtime-wrappers: factor out efi_rts_park_worker()

x86's efi_crash_gracefully_on_page_fault() ends in an infinite
schedule() loop so the kworker that faulted in firmware never runs
efi_rts_wq again. A later change needs the same "park this worker
forever" primitive on the runtime service timeout path, so factor the
loop into a shared efi_rts_park_worker() and call it from the x86
page-fault handler.

No functional change.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/x86/platform/efi/quirks.c

@@ -832,12 +832,5 @@ void efi_crash_gracefully_on_page_fault(unsigned long phys_addr,
 	clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
 	pr_info("Froze efi_rts_wq and disabled EFI Runtime Services\n");
 
-	/*
-	 * Call schedule() in an infinite loop, so that any spurious wake ups
-	 * will never run efi_rts_wq again.
-	 */
-	for (;;) {
-		set_current_state(TASK_IDLE);
-		schedule();
-	}
+	efi_rts_park_worker();
 }

drivers/firmware/efi/runtime-wrappers.c

@@ -211,6 +211,19 @@ static struct task_struct *efi_runtime_lock_owner;
 extern struct semaphore __efi_uv_runtime_lock __alias(efi_runtime_lock);
 #endif
 
+/*
+ * Park a worker that must never run efi_rts_wq again: EFI runtime services
+ * have been disabled and its efi_rts_work is abandoned. Loop in schedule()
+ * so a spurious wakeup cannot resume it.
+ */
+void efi_rts_park_worker(void)
+{
+	for (;;) {
+		set_current_state(TASK_IDLE);
+		schedule();
+	}
+}
+
 /*
  * Calls the appropriate efi_runtime_service() with the appropriate
  * arguments.

include/linux/efi.h

@@ -1256,6 +1256,8 @@ extern struct efi_runtime_work efi_rts_work;
 /* Workqueue to queue EFI Runtime Services */
 extern struct workqueue_struct *efi_rts_wq;
 
+void efi_rts_park_worker(void);
+
 struct linux_efi_memreserve {
 	int		size;			// allocated size of the array
 	atomic_t	count;			// number of entries used