linux-kernel - [PATCH v2] block: use dedicated list iterator variable

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Date:   Thu, 31 Mar 2022 11:12:18 +0200
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bart Van Assche <bvanassche@....org>,
        Mike Rapoport <rppt@...nel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jakobkoschel@...il.com>
Subject: [PATCH v2] block: use dedicated list iterator variable

To move the list iterator variable into the list_for_each_entry_*()
macro in the future it should be avoided to use the list iterator
variable after the loop body.

To *never* use the list iterator variable after the loop it was
concluded to use a separate iterator variable instead of a
found boolean [1].

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
---

v1->v2:
- introduce blk_lookup_qe_pair() for more readable code (Bart Van Assche)

 block/blk-mq.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index e6f24fa4a4c2..f7f950cce452 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4462,21 +4462,27 @@ static bool blk_mq_elv_switch_none(struct list_head *head,
 	return true;
 }

-static void blk_mq_elv_switch_back(struct list_head *head,
-		struct request_queue *q)
+static struct blk_mq_qe_pair *blk_lookup_qe_pair(struct list_head *head,
+						struct request_queue *q)
 {
 	struct blk_mq_qe_pair *qe;
-	struct elevator_type *t = NULL;

 	list_for_each_entry(qe, head, node)
-		if (qe->q == q) {
-			t = qe->type;
-			break;
-		}
+		if (qe->q == q)
+			return qe;

-	if (!t)
-		return;
+	return NULL;
+}
+
+static void blk_mq_elv_switch_back(struct list_head *head,
+				  struct request_queue *q)
+{
+	struct blk_mq_qe_pair *qe = blk_lookup_qe_pair(head, q);
+	struct elevator_type *t;

+	if (!qe)
+		return;
+	t = qe->type;
 	list_del(&qe->node);
 	kfree(qe);


base-commit: d888c83fcec75194a8a48ccd283953bdba7b2550
--
2.25.1