linux-kernel - [PATCH] wifi: mac80211: tx: Add __must

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Date: Fri, 12 Jan 2024 20:11:45 -0500
From: Brent Pappas <bpappas@...pasbrent.com>
To: Johannes Berg <johannes@...solutions.net>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Brent Pappas <bpappas@...pasbrent.com>,
	linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] wifi: mac80211: tx: Add __must_hold() annotation

Annotates ieee80211_set_beacon_cntdwn() with a __must_hold() annotation to
make it clear that ieee80211_set_beacon_cntdwn() is only intended to be
called when the caller has a lock on the argument "link."

Signed-off-by: Brent Pappas <bpappas@...pasbrent.com>
---

Currently, ieee80211_set_beacon_cntdwn() calls rcu_dereference(), but
without calling rcu_read_lock() beforehand and rcu_read_unlock()
afterward.  At first I thought this was a bug, since (if I understand the
RCU API correctly) rcu_dereference() should only be called in RCU
read-side critical sections. However, upon closer inspection of the code,
I realized that ieee80211_set_beacon_cntdwn() is only ever called inside
critical sections. Therefore it seems appropriate to me to annotate
ieee80211_set_beacon_cntdwn() with a __must_hold() annotation to make this
apparent precondition explicit.

This is my first time submitting an RCU-related patch so please tell me if
I am misunderstanding the RCU API.

 net/mac80211/tx.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 314998fdb1a5..7245f2e641ba 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -10,6 +10,7 @@
  * Transmit and frame generation functions.
  */

+#include "linux/compiler_types.h"
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/skbuff.h>
@@ -4974,6 +4975,7 @@ static int ieee80211_beacon_add_tim(struct ieee80211_sub_if_data *sdata,
 static void ieee80211_set_beacon_cntdwn(struct ieee80211_sub_if_data *sdata,
 					struct beacon_data *beacon,
 					struct ieee80211_link_data *link)
+	__must_hold(link)
 {
 	u8 *beacon_data, count, max_count = 1;
 	struct probe_resp *resp;
-- 
2.43.0