netdev - Re: [PATCH net] Revert "net: phy: Correctly process PHY_HALTED in phy_stop

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Date:   Thu, 31 Aug 2017 19:49:47 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Florian Fainelli <f.fainelli@...il.com>,
        David Daney <ddaney.cavm@...il.com>
Cc:     Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        netdev <netdev@...r.kernel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        David Miller <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>, Mans Rullgard <mans@...sr.com>
Subject: Re: [PATCH net] Revert "net: phy: Correctly process PHY_HALTED in
 phy_stop_machine()"

On 31/08/2017 18:57, Florian Fainelli wrote:
> And the race is between phy_detach() setting phydev->attached_dev = NULL
> and phy_state_machine() running in PHY_HALTED state and calling
> netif_carrier_off().

I must be missing something.
(Since a thread cannot race against itself.)

phy_disconnect calls phy_stop_machine which
1) stops the work queue from running in a separate thread
2) calls phy_state_machine *synchronously*
     which runs the PHY_HALTED case with everything well-defined
end of phy_stop_machine

phy_disconnect only then calls phy_detach()
which makes future calls of phy_state_machine perilous.

This all happens in the same thread, so I'm not yet
seeing where the race happens?

Regards.