On Fri, 17 Jan 2025 13:57:41 +0200
Claudiu Beznea [off-list ref] wrote:

Hi, Kory,

On 12.12.2024 19:06, Kory Maincent wrote:

quoted

Introduce the description of a hwtstamp provider, mainly defined with a
the hwtstamp source and the phydev pointer.

Add a hwtstamp provider description within the netdev structure to
allow saving the hwtstamp we want to use. This prepares for future
support of an ethtool netlink command to select the desired hwtstamp
provider. By default, the old API that does not support hwtstamp
selectability is used, meaning the hwtstamp provider pointer is unset.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>  

I'm getting this error when doing suspend/resume on the Renesas RZ/G3S
Smarc Module + RZ SMARC Carrier II board:

[   39.032969] =============================
[   39.032983] WARNING: suspicious RCU usage
[   39.033000] 6.13.0-rc7-next-20250116-arm64-renesas-00002-g35245dfdc62c
#7 Not tainted
[   39.033019] -----------------------------
[   39.033033] drivers/net/phy/phy_device.c:2004 suspicious
rcu_dereference_protected() usage!

Thanks for the report.
Oh so it seems there are cases where phy_detach is not called under RTNL lock!

This should solve the issue:
-               hwprov = rtnl_dereference(dev->hwprov);
+               rcu_read_lock()
+               hwprov = rcu_dereference(dev->hwprov);
                /* Disable timestamp if it is the one selected */
                if (hwprov && hwprov->phydev == phydev) {
                        rcu_assign_pointer(dev->hwprov, NULL);
                        kfree_rcu(hwprov, rcu_head);
                }
+               rcu_read_unlock();

I will send a patch soon.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com