netdev - [PATCH net] net: sched: gred: prevent races when adding offloads to stats

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Date:   Thu, 12 Jan 2023 20:41:37 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Functional Testing <lkft@...aro.org>,
        jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        john.hurley@...ronome.com
Subject: [PATCH net] net: sched: gred: prevent races when adding offloads to stats

Naresh reports seeing a warning that gred is calling
u64_stats_update_begin() with preemption enabled.
Arnd points out it's coming from _bstats_update().

We should be holding the qdisc lock when writing
to stats, they are also updated from the datapath.

Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
Link: https://lore.kernel.org/all/CA+G9fYsTr9_r893+62u6UGD3dVaCE-kN9C-Apmb2m=hxjc1Cqg@mail.gmail.com/
Fixes: e49efd5288bd ("net: sched: gred: support reporting stats from offloads")
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
CC: jhs@...atatu.com
CC: xiyou.wangcong@...il.com
CC: jiri@...nulli.us
CC: john.hurley@...ronome.com
---
 net/sched/sch_gred.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sched/sch_gred.c b/net/sched/sch_gred.c
index a661b062cca8..872d127c9db4 100644
--- a/net/sched/sch_gred.c
+++ b/net/sched/sch_gred.c
@@ -377,6 +377,7 @@ static int gred_offload_dump_stats(struct Qdisc *sch)
 	/* Even if driver returns failure adjust the stats - in case offload
 	 * ended but driver still wants to adjust the values.
 	 */
+	sch_tree_lock(sch);
 	for (i = 0; i < MAX_DPs; i++) {
 		if (!table->tab[i])
 			continue;
@@ -393,6 +394,7 @@ static int gred_offload_dump_stats(struct Qdisc *sch)
 		sch->qstats.overlimits += hw_stats->stats.qstats[i].overlimits;
 	}
 	_bstats_update(&sch->bstats, bytes, packets);
+	sch_tree_unlock(sch);
 
 	kfree(hw_stats);
 	return ret;
-- 
2.38.1