From 55f656cdb851bae32980d83d2494201e79d93b63 Mon Sep 17 00:00:00 2001
From: Petr Machata <petrm@mellanox.com>
Date: Tue, 14 Jul 2020 20:03:07 +0300
Subject: net: sched: Do not drop root lock in tcf_qevent_handle()
Mirred currently does not mix well with blocks executed after the qdisc
root lock is taken. This includes classification blocks (such as in PRIO,
ETS, DRR qdiscs) and qevents. The locking caused by the packet mirrored by
mirred can cause deadlocks: either when the thread of execution attempts to
take the lock a second time, or when two threads end up waiting on each
other's locks.
The qevent patchset attempted to not introduce further badness of this
sort, and dropped the lock before executing the qevent block. However this
lead to too little locking and races between qdisc configuration and packet
enqueue in the RED qdisc.
Before the deadlock issues are solved in a way that can be applied across
many qdiscs reasonably easily, do for qevents what is done for the
classification blocks and just keep holding the root lock.
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
net/sched/cls_api.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
(limited to 'net/sched/cls_api.c')
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 322b279154de..b2b7440c2ae7 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -3822,7 +3822,7 @@ int tcf_qevent_validate_change(struct tcf_qevent *qe, struct nlattr *block_index
EXPORT_SYMBOL(tcf_qevent_validate_change);
struct sk_buff *tcf_qevent_handle(struct tcf_qevent *qe, struct Qdisc *sch, struct sk_buff *skb,
- spinlock_t *root_lock, struct sk_buff **to_free, int *ret)
+ struct sk_buff **to_free, int *ret)
{
struct tcf_result cl_res;
struct tcf_proto *fl;
@@ -3832,9 +3832,6 @@ struct sk_buff *tcf_qevent_handle(struct tcf_qevent *qe, struct Qdisc *sch, stru
fl = rcu_dereference_bh(qe->filter_chain);
- if (root_lock)
- spin_unlock(root_lock);
-
switch (tcf_classify(skb, fl, &cl_res, false)) {
case TC_ACT_SHOT:
qdisc_qstats_drop(sch);
@@ -3853,9 +3850,6 @@ struct sk_buff *tcf_qevent_handle(struct tcf_qevent *qe, struct Qdisc *sch, stru
return NULL;
}
- if (root_lock)
- spin_lock(root_lock);
-
return skb;
}
EXPORT_SYMBOL(tcf_qevent_handle);
--
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