linux-kernel - [PATCH 1/2] dm snapshot: remove usage of list iterator for list

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Message-Id: <20220331220236.884887-1-jakobkoschel@gmail.com>
Date:   Fri,  1 Apr 2022 00:02:35 +0200
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Alasdair Kergon <agk@...hat.com>
Cc:     Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.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 1/2] dm snapshot: remove usage of list iterator for list_add() after the loop body

In preparation to limit the scope of a list iterator to the list
traversal loop, use a dedicated pointer to point to the found element
[1].

Before, the code implicitly used the head when no element was found
when using &pos->list. Since the new variable is only set if an
element was found, the list_add() is performed within the loop
and only done after the loop if it is done on the list head directly.

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
---
 drivers/md/dm-snap.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 0d336b5ec571..23386a6e67e7 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -528,13 +528,17 @@ static int __validate_exception_handover(struct dm_snapshot *snap)
 
 static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
 {
-	struct dm_snapshot *l;
+	struct dm_snapshot *l = NULL, *iter;
 
 	/* Sort the list according to chunk size, largest-first smallest-last */
-	list_for_each_entry(l, &o->snapshots, list)
-		if (l->store->chunk_size < s->store->chunk_size)
+	list_for_each_entry(iter, &o->snapshots, list)
+		if (iter->store->chunk_size < s->store->chunk_size) {
+			l = iter;
+			list_add_tail(&s->list, &iter->list);
 			break;
-	list_add_tail(&s->list, &l->list);
+		}
+	if (!l)
+		list_add_tail(&s->list, &o->snapshots);
 }
 
 /*

base-commit: f82da161ea75dc4db21b2499e4b1facd36dab275
-- 
2.25.1