From: Mason <slash.tmp@free.fr>
To: Florian Fainelli <f.fainelli@gmail.com>,
David Daney <ddaney.cavm@gmail.com>
Cc: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>,
netdev <netdev@vger.kernel.org>,
Geert Uytterhoeven <geert+renesas@glider.be>,
David Miller <davem@davemloft.net>, Andrew Lunn <andrew@lunn.ch>,
Mans Rullgard <mans@mansr.com>
Subject: Re: [PATCH net] Revert "net: phy: Correctly process PHY_HALTED in phy_stop_machine()"
Date: Thu, 31 Aug 2017 20:12:42 +0200 [thread overview]
Message-ID: <ebee6e5d-5bc1-1c5b-b31d-6d50618d6074@free.fr> (raw)
In-Reply-To: <f74f1aad-3990-ae54-316f-751c3b15de41@gmail.com>
On 31/08/2017 19:53, Florian Fainelli wrote:
> On 08/31/2017 10:49 AM, Mason wrote:
>> 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?
>
> The race is as described in David's earlier email, so let's recap:
>
> Thread 1 Thread 2
> phy_disconnect()
> phy_stop_interrupts()
> phy_stop_machine()
> phy_state_machine()
> -> queue_delayed_work()
> phy_detach()
> phy_state_machine()
> -> netif_carrier_off()
>
> If phy_detach() finishes earlier than the workqueue had a chance to be
> scheduled and process PHY_HALTED again, then we trigger the NULL pointer
> de-reference.
>
> workqueues are not tasklets, the CPU scheduling them gets no guarantee
> they will run on the same CPU.
Something does not add up.
The synchronous call to phy_state_machine() does:
case PHY_HALTED:
if (phydev->link) {
phydev->link = 0;
netif_carrier_off(phydev->attached_dev);
phy_adjust_link(phydev);
do_suspend = true;
}
then sets phydev->link = 0; therefore subsequent calls to
phy_state_machin() will be no-op.
Also, queue_delayed_work() is only called in polling mode.
David stated that he's using interrupt mode.
Regards.
next prev parent reply other threads:[~2017-08-31 18:12 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-31 0:49 [PATCH net] Revert "net: phy: Correctly process PHY_HALTED in phy_stop_machine()" Florian Fainelli
2017-08-31 1:47 ` David Miller
2017-08-31 12:29 ` Marc Gonzalez
2017-08-31 14:21 ` Marc Gonzalez
2017-08-31 16:36 ` David Daney
2017-08-31 16:57 ` Florian Fainelli
2017-08-31 17:49 ` Mason
2017-08-31 17:53 ` Florian Fainelli
2017-08-31 18:12 ` Mason [this message]
2017-08-31 18:29 ` Florian Fainelli
2017-09-06 14:33 ` Mason
2017-09-06 17:53 ` David Daney
2017-09-06 18:00 ` David Daney
2017-09-06 18:59 ` Florian Fainelli
2017-09-06 20:49 ` David Daney
2017-09-06 22:51 ` David Daney
2017-09-06 23:14 ` Florian Fainelli
2017-09-07 0:10 ` David Daney
2017-09-07 1:41 ` Florian Fainelli
2017-09-06 19:14 ` Mason
2017-08-31 17:35 ` Mason
2017-08-31 17:03 ` Florian Fainelli
2017-08-31 19:09 ` Mason
2017-08-31 19:18 ` Florian Fainelli
2017-09-06 14:55 ` Mason
2017-09-06 19:28 ` Florian Fainelli
2017-09-06 15:51 ` Mason
2017-09-06 19:42 ` Florian Fainelli
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