Re: [PATCH net-next v2] net: phy: Fix suspicious rcu_dereference usage

On Mon, Jan 20, 2025 at 10:37:22AM +0100, Kory Maincent wrote:

On Fri, 17 Jan 2025 19:07:20 -0800
Jakub Kicinski [off-list ref] wrote:

quoted

On Fri, 17 Jan 2025 23:16:59 +0100 Kory Maincent wrote:

quoted

quoted

If not protected by RTNL, what prevents two threads from calling this
function at the same time,
thus attempting to kfree_rcu() the same pointer twice ?    

I don't think this function can be called simultaneously from two threads,
if this were the case we would have already seen several issues with the
phydev pointer. But maybe I am wrong.

The rcu_lock here is to prevent concurrent dev->hwprov pointer modification
done under rtnl_lock in net/ethtool/tsconfig.c.  

I could also be wrong, but I don't recall being told that suspend path
can't race with anything else. So I think ravb should probably take
rtnl_lock or some such when its shutting itself down.. ?

If I'm wrong I think we should mention this is from suspend and
add Claudiu's stack trace to the commit msg.

Is it ok if I send the v3 fix in net-next even if it is closed?

In general, fixes are still accepted into net-next if the pull request
hasn't been sent and the code that is being fixed is only in net-next.

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