netdev - [PATCH net-next 2/2] net: dsa: warn about dsa_port and dsa

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Message-Id: <20220105221150.3208247-2-vladimir.oltean@nxp.com>
Date:   Thu,  6 Jan 2022 00:11:50 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: [PATCH net-next 2/2] net: dsa: warn about dsa_port and dsa_switch bit fields being non atomic

As discussed during review here:
https://patchwork.kernel.org/project/netdevbpf/patch/20220105132141.2648876-3-vladimir.oltean@nxp.com/

we should inform developers about pitfalls of concurrent access to the
boolean properties of dsa_switch and dsa_port, now that they've been
converted to bit fields. No other measure than a comment needs to be
taken, since the code paths that update these bit fields are not
concurrent with each other.

Suggested-by: Florian Fainelli <f.fainelli@...il.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 include/net/dsa.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 63c7f553f938..57b3e4e7413b 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -265,6 +265,10 @@ struct dsa_port {
 
 	u8			stp_state;
 
+	/* Warning: the following bit fields are not atomic, and updating them
+	 * can only be done from code paths where concurrency is not possible
+	 * (probe time or under rtnl_lock).
+	 */
 	u8			vlan_filtering:1;
 
 	/* Managed by DSA on user ports and by drivers on CPU and DSA ports */
@@ -333,6 +337,10 @@ struct dsa_switch {
 	struct dsa_switch_tree	*dst;
 	unsigned int		index;
 
+	/* Warning: the following bit fields are not atomic, and updating them
+	 * can only be done from code paths where concurrency is not possible
+	 * (probe time or under rtnl_lock).
+	 */
 	u32			setup:1;
 
 	/* Disallow bridge core from requesting different VLAN awareness
-- 
2.25.1