netdev - [PATCH net] net: dsa: restore error path of dsa_tree_change_tag

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Message-Id: <20220228141715.146485-1-vladimir.oltean@nxp.com>
Date:   Mon, 28 Feb 2022 16:17:15 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Ansuel Smith <ansuelsmth@...il.com>
Subject: [PATCH net] net: dsa: restore error path of dsa_tree_change_tag_proto

When the DSA_NOTIFIER_TAG_PROTO returns an error, the user space process
which initiated the protocol change exits the kernel processing while
still holding the rtnl_mutex. So any other process attempting to lock
the rtnl_mutex would deadlock after such event.

The error handling of DSA_NOTIFIER_TAG_PROTO was inadvertently changed
by the blamed commit, introducing this regression. We must still call
rtnl_unlock(), and we must still call DSA_NOTIFIER_TAG_PROTO for the old
protocol. The latter is due to the limiting design of notifier chains
for cross-chip operations, which don't have a built-in error recovery
mechanism - we should look into using notifier_call_chain_robust for that.

Fixes: dc452a471dba ("net: dsa: introduce tagger-owned storage for private and shared data")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/dsa/dsa2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index 030d5f26715a..d3f9dbd3a815 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -1294,7 +1294,7 @@ int dsa_tree_change_tag_proto(struct dsa_switch_tree *dst,
 	info.tag_ops = tag_ops;
 	err = dsa_tree_notify(dst, DSA_NOTIFIER_TAG_PROTO, &info);
 	if (err)
-		return err;
+		goto out_unlock;

 	err = dsa_tree_bind_tag_proto(dst, tag_ops);
 	if (err)
-- 
2.25.1