[PATCH net] Revert "net: dev: introduce support for sch BYPASS for lockless qdisc"

[PATCH net] Revert "net: dev: introduce support for sch BYPASS for lockless qdisc"

[Paolo Abeni]

This reverts commit ba27b4cdaaa66561aaedb2101876e563738d36fe

Ahmed reported ouf-of-order issues bisected to commit ba27b4cdaaa6
("net: dev: introduce support for sch BYPASS for lockless qdisc").
I can't find any working solution other than a plain revert.

This will introduce some minor performance regressions for
pfifo_fast qdisc. I plan to address them in net-next with more
indirect call wrapper boilerplate for qdiscs.

Reported-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Fixes: ba27b4cdaaa6 ("net: dev: introduce support for sch BYPASS for lockless qdisc")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
Due to pathological lack of coffee, a previous copy did not
land on the netdev ML, I'm sorry for the noise on CC addresses
---
 net/core/dev.c | 22 ++--------------------
 1 file changed, 2 insertions(+), 20 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 2577ebfed293..e10bd680dc03 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3662,26 +3662,8 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 	qdisc_calculate_pkt_len(skb, q);
 
 	if (q->flags & TCQ_F_NOLOCK) {
-		if ((q->flags & TCQ_F_CAN_BYPASS) && READ_ONCE(q->empty) &&
-		    qdisc_run_begin(q)) {
-			if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED,
-					      &q->state))) {
-				__qdisc_drop(skb, &to_free);
-				rc = NET_XMIT_DROP;
-				goto end_run;
-			}
-			qdisc_bstats_cpu_update(q, skb);
-
-			rc = NET_XMIT_SUCCESS;
-			if (sch_direct_xmit(skb, q, dev, txq, NULL, true))
-				__qdisc_run(q);
-
-end_run:
-			qdisc_run_end(q);
-		} else {
-			rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
-			qdisc_run(q);
-		}
+		rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
+		qdisc_run(q);
 
 		if (unlikely(to_free))
 			kfree_skb_list(to_free);
-- 
2.21.1

Re: [PATCH net] Revert "net: dev: introduce support for sch BYPASS for lockless qdisc"

[David Miller]

From: Paolo Abeni <pabeni@redhat.com>
Date: Tue, 18 Feb 2020 18:15:44 +0100

> This reverts commit ba27b4cdaaa66561aaedb2101876e563738d36fe
> 
> Ahmed reported ouf-of-order issues bisected to commit ba27b4cdaaa6
> ("net: dev: introduce support for sch BYPASS for lockless qdisc").
> I can't find any working solution other than a plain revert.
> 
> This will introduce some minor performance regressions for
> pfifo_fast qdisc. I plan to address them in net-next with more
> indirect call wrapper boilerplate for qdiscs.
> 
> Reported-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> Fixes: ba27b4cdaaa6 ("net: dev: introduce support for sch BYPASS for lockless qdisc")
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Applied and queued up for -stable, thanks.