linux-kernel - [PATCH 2/3] ASoC: sprd: remove check of list iterator against head past the loop body

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Message-Id: <20220331215003.882143-2-jakobkoschel@gmail.com>
Date:   Thu, 31 Mar 2022 23:50:02 +0200
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Jie Yang <yang.jie@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang7@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Yang Yingliang <yangyingliang@...wei.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        alsa-devel@...a-project.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 2/3] ASoC: sprd: remove check of list iterator against head past the loop body

When list_for_each_entry() completes the iteration over the whole list
without breaking the loop, the iterator value will be a bogus pointer
computed based on the head element.

While it is safe to use the pointer to determine if it was computed
based on the head element, either with list_entry_is_head() or
&pos->member == head, using the iterator variable after the loop should
be avoided.

In preparation to limiting the scope of a list iterator to the list
traversal loop, use a dedicated pointer to point to the found element [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>
---
 sound/soc/sprd/sprd-mcdt.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/sound/soc/sprd/sprd-mcdt.c b/sound/soc/sprd/sprd-mcdt.c
index f6a55fa60c1b..6e27789a0df5 100644
--- a/sound/soc/sprd/sprd-mcdt.c
+++ b/sound/soc/sprd/sprd-mcdt.c
@@ -866,20 +866,19 @@ EXPORT_SYMBOL_GPL(sprd_mcdt_chan_dma_disable);
 struct sprd_mcdt_chan *sprd_mcdt_request_chan(u8 channel,
 					      enum sprd_mcdt_channel_type type)
 {
-	struct sprd_mcdt_chan *temp;
+	struct sprd_mcdt_chan *temp = NULL;
+	struct sprd_mcdt_chan *iter;
 
 	mutex_lock(&sprd_mcdt_list_mutex);
 
-	list_for_each_entry(temp, &sprd_mcdt_chan_list, list) {
-		if (temp->type == type && temp->id == channel) {
-			list_del_init(&temp->list);
+	list_for_each_entry(iter, &sprd_mcdt_chan_list, list) {
+		if (iter->type == type && iter->id == channel) {
+			list_del_init(&iter->list);
+			temp = iter;
 			break;
 		}
 	}
 
-	if (list_entry_is_head(temp, &sprd_mcdt_chan_list, list))
-		temp = NULL;
-
 	mutex_unlock(&sprd_mcdt_list_mutex);
 
 	return temp;
-- 
2.25.1