netdev - [PATCH net-next 1/2] net: sched: fix logic error in qdisc_run

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Date:   Mon, 18 Oct 2021 17:34:01 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "Ahmed S . Darwish" <a.darwish@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH net-next 1/2] net: sched: fix logic error in qdisc_run_begin()

From: Eric Dumazet <edumazet@...gle.com>

For non TCQ_F_NOLOCK qdisc, qdisc_run_begin() tries to set
__QDISC_STATE_RUNNING and should return true if the bit was not set.

test_and_set_bit() returns old bit value, therefore we need to invert.

Fixes: 29cbcd858283 ("net: sched: Remove Qdisc::running sequence counter")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Ahmed S. Darwish <a.darwish@...utronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 include/net/sch_generic.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index baad2ab4d971cd3fdc8d59acdd72d39fa6230370..e0988c56dd8fd7aa3dff6bd971da3c81f1a20626 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -217,7 +217,7 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 		 */
 		return spin_trylock(&qdisc->seqlock);
 	}
-	return test_and_set_bit(__QDISC_STATE_RUNNING, &qdisc->state);
+	return !test_and_set_bit(__QDISC_STATE_RUNNING, &qdisc->state);
 }
 
 static inline void qdisc_run_end(struct Qdisc *qdisc)
-- 
2.33.0.1079.g6e70778dc9-goog