[PATCH v4 6/6] block: fix default IO priority handling

[Damien Le Moal <damien.lemoal@wdc.com>]

The default IO priority is the best effort (BE) class with the
normal priority level IOPRIO_NORM (4). However, get_task_ioprio()
returns IOPRIO_CLASS_NONE/IOPRIO_NORM as the default priority and
get_current_ioprio() returns IOPRIO_CLASS_NONE/0. Let's be consistent
with the defined default and have both of these functions return the
default priority IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM) when
the user did not define another default IO priority for the task.

In include/uapi/linux/ioprio.h, introduce the IOPRIO_BE_NORM macro as
an alias to IOPRIO_NORM to clarify that this default level applies to
the BE priotity class. In include/linux/ioprio.h, define the macro
IOPRIO_DEFAULT as IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_BE_NORM)
and use this new macro when setting a priority to the default.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
---
 block/bfq-iosched.c          | 2 +-
 block/ioprio.c               | 6 +++---
 drivers/nvme/host/lightnvm.c | 2 +-
 include/linux/ioprio.h       | 7 ++++++-
 include/uapi/linux/ioprio.h  | 5 +++--
 5 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 4b434369e411..e92bc0348433 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5411,7 +5411,7 @@ static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
 	case IOPRIO_CLASS_RT:
 		return &bfqg->async_bfqq[0][ioprio];
 	case IOPRIO_CLASS_NONE:
-		ioprio = IOPRIO_NORM;
+		ioprio = IOPRIO_BE_NORM;
 		fallthrough;
 	case IOPRIO_CLASS_BE:
 		return &bfqg->async_bfqq[1][ioprio];
diff --git a/block/ioprio.c b/block/ioprio.c
index ca6b136c5586..0e4ff245f2bf 100644
--- a/block/ioprio.c
+++ b/block/ioprio.c
@@ -170,7 +170,7 @@ static int get_task_ioprio(struct task_struct *p)
 	ret = security_task_getioprio(p);
 	if (ret)
 		goto out;
-	ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
+	ret = IOPRIO_DEFAULT;
 	task_lock(p);
 	if (p->io_context)
 		ret = p->io_context->ioprio;
@@ -182,9 +182,9 @@ static int get_task_ioprio(struct task_struct *p)
 int ioprio_best(unsigned short aprio, unsigned short bprio)
 {
 	if (!ioprio_valid(aprio))
-		aprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);
+		aprio = IOPRIO_DEFAULT;
 	if (!ioprio_valid(bprio))
-		bprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);
+		bprio = IOPRIO_DEFAULT;
 
 	return min(aprio, bprio);
 }
diff --git a/drivers/nvme/host/lightnvm.c b/drivers/nvme/host/lightnvm.c
index e9d9ad47f70f..0fbbff0b3edb 100644
--- a/drivers/nvme/host/lightnvm.c
+++ b/drivers/nvme/host/lightnvm.c
@@ -662,7 +662,7 @@ static struct request *nvme_nvm_alloc_request(struct request_queue *q,
 	if (rqd->bio)
 		blk_rq_append_bio(rq, rqd->bio);
 	else
-		rq->ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);
+		rq->ioprio = IOPRIO_DEFAULT;
 
 	return rq;
 }
diff --git a/include/linux/ioprio.h b/include/linux/ioprio.h
index 2ee3373684b1..3f53bc27a19b 100644
--- a/include/linux/ioprio.h
+++ b/include/linux/ioprio.h
@@ -8,6 +8,11 @@
 
 #include <uapi/linux/ioprio.h>
 
+/*
+ * Default IO priority.
+ */
+#define IOPRIO_DEFAULT	IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_BE_NORM)
+
 /*
  * Check that a priority value has a valid class.
  */
@@ -51,7 +56,7 @@ static inline int get_current_ioprio(void)
 
 	if (ioc)
 		return ioc->ioprio;
-	return IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
+	return IOPRIO_DEFAULT;
 }
 
 /*
diff --git a/include/uapi/linux/ioprio.h b/include/uapi/linux/ioprio.h
index aac39338d02c..f70f2596a6bf 100644
--- a/include/uapi/linux/ioprio.h
+++ b/include/uapi/linux/ioprio.h
@@ -44,8 +44,9 @@ enum {
 };
 
 /*
- * Fallback BE priority
+ * Fallback BE priority level.
  */
-#define IOPRIO_NORM	(4)
+#define IOPRIO_NORM	4
+#define IOPRIO_BE_NORM	IOPRIO_NORM
 
 #endif /* _UAPI_LINUX_IOPRIO_H */
-- 
2.31.1