1 files changed, 50 insertions, 8 deletions

diff --git a/block/ioprio.c b/block/ioprio.c
index 2fe068fcaad5..32a456b45804 100644
--- a/block/ioprio.c
+++ b/block/ioprio.c
@@ -138,6 +138,32 @@ out:
 	return ret;
 }
 
+/*
+ * If the task has set an I/O priority, use that. Otherwise, return
+ * the default I/O priority.
+ *
+ * Expected to be called for current task or with task_lock() held to keep
+ * io_context stable.
+ */
+int __get_task_ioprio(struct task_struct *p)
+{
+	struct io_context *ioc = p->io_context;
+	int prio;
+
+	if (p != current)
+		lockdep_assert_held(&p->alloc_lock);
+	if (ioc)
+		prio = ioc->ioprio;
+	else
+		prio = IOPRIO_DEFAULT;
+
+	if (IOPRIO_PRIO_CLASS(prio) == IOPRIO_CLASS_NONE)
+		prio = IOPRIO_PRIO_VALUE(task_nice_ioclass(p),
+					 task_nice_ioprio(p));
+	return prio;
+}
+EXPORT_SYMBOL_GPL(__get_task_ioprio);
+
 static int get_task_ioprio(struct task_struct *p)
 {
 	int ret;
@@ -145,22 +171,38 @@ static int get_task_ioprio(struct task_struct *p)
 	ret = security_task_getioprio(p);
 	if (ret)
 		goto out;
-	ret = IOPRIO_DEFAULT;
+	task_lock(p);
+	ret = __get_task_ioprio(p);
+	task_unlock(p);
+out:
+	return ret;
+}
+
+/*
+ * Return raw IO priority value as set by userspace. We use this for
+ * ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and
+ * also so that userspace can distinguish unset IO priority (which just gets
+ * overriden based on task's nice value) from IO priority set to some value.
+ */
+static int get_task_raw_ioprio(struct task_struct *p)
+{
+	int ret;
+
+	ret = security_task_getioprio(p);
+	if (ret)
+		goto out;
 	task_lock(p);
 	if (p->io_context)
 		ret = p->io_context->ioprio;
+	else
+		ret = IOPRIO_DEFAULT;
 	task_unlock(p);
 out:
 	return ret;
 }
 
-int ioprio_best(unsigned short aprio, unsigned short bprio)
+static int ioprio_best(unsigned short aprio, unsigned short bprio)
 {
-	if (!ioprio_valid(aprio))
-		aprio = IOPRIO_DEFAULT;
-	if (!ioprio_valid(bprio))
-		bprio = IOPRIO_DEFAULT;
-
 	return min(aprio, bprio);
 }
 
@@ -181,7 +223,7 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
 			else
 				p = find_task_by_vpid(who);
 			if (p)
-				ret = get_task_ioprio(p);
+				ret = get_task_raw_ioprio(p);
 			break;
 		case IOPRIO_WHO_PGRP:
 			if (!who)