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

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Message-ID: <64800ff2-201b-eb26-304e-1c4c6e0a6d5e@caviumnetworks.com>
Date:   Wed, 6 Sep 2017 17:10:02 -0700
From:   David Daney <ddaney@...iumnetworks.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        David Daney <ddaney.cavm@...il.com>, Mason <slash.tmp@...e.fr>
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 09/06/2017 04:14 PM, Florian Fainelli wrote:
> On 09/06/2017 03:51 PM, David Daney wrote:
[...]
>>
>> Consider instead the case of a Marvell phy with no interrupts connected
>> on a v4.9.43 kernel, single CPU:
>>
>>
>>    0)               |                 phy_disconnect() {
>>    0)               |                   phy_stop_machine() {
>>    0)               |                     cancel_delayed_work_sync() {
>>    0) + 23.986 us   |                     } /* cancel_delayed_work_sync */
>>    0)               |                     phy_state_machine() {
>>    0)               |                       phy_start_aneg_priv() {
> 
> Thanks for providing the trace, I think I have an idea of what's going
> on, see below.
> 
>>    0)               |                         marvell_config_aneg() {
>>    0) ! 240.538 us  |                         } /* marvell_config_aneg */
>>    0) ! 244.971 us  |                       } /* phy_start_aneg_priv */
>>    0)               |                       queue_delayed_work_on() {
>>    0) + 18.016 us   |                       } /* queue_delayed_work_on */
>>    0) ! 268.184 us  |                     } /* phy_state_machine */
>>    0) ! 297.394 us  |                   } /* phy_stop_machine */
>>    0)               |                   phy_detach() {
>>    0)               |                     phy_suspend() {
>>    0)               |                       phy_ethtool_get_wol() {
>>    0)   0.677 us    |                       } /* phy_ethtool_get_wol */
>>    0)               |                       genphy_suspend() {
>>    0) + 71.250 us   |                       } /* genphy_suspend */
>>    0) + 74.197 us   |                     } /* phy_suspend */
>>    0) + 80.302 us   |                   } /* phy_detach */
>>    0) ! 380.072 us  |                 } /* phy_disconnect */
>> .
>> .
>> .
>>    0)               |  process_one_work() {
>>    0)               |    find_worker_executing_work() {
>>    0)   0.688 us    |    } /* find_worker_executing_work */
>>    0)               |    set_work_pool_and_clear_pending() {
>>    0)   0.734 us    |    } /* set_work_pool_and_clear_pending */
>>    0)               |    phy_state_machine() {
>>    0)               |      genphy_read_status() {
>>    0) ! 205.721 us  |      } /* genphy_read_status */
>>    0)               |      netif_carrier_off() {
>>    0)               |        do_page_fault() {
>>
>>
>> The do_page_fault() at the end indicates the NULL pointer dereference.
>>
>> That added call to phy_state_machine() turns the polling back on
>> unconditionally for a phy that should be disconnected.  How is that
>> correct?
> 
> It is not fundamentally correct and I don't think there was any
> objection to that to begin with. In fact there is a bug/inefficiency
> here in that if we have entered the PHY state machine with PHY_HALTED we
> should not re-schedule it period, only applicable to PHY_POLL cases
> *and* properly calling phy_stop() followed by phy_disconnect().
> 
> What I now think is happening in your case is the following:
> 
> phy_stop() was not called, so nothing does set phydev->state to
> PHY_HALTED in the first place so we have:
> 
> phy_disconnect()
> -> phy_stop_machine()
> 	-> cancel_delayed_work_sync() OK
> 		phydev->state is probably RUNNING so we have:
> 		-> phydev->state = PHY_UP
> 	phy_state_machine() is called synchronously
> 	-> PHY_UP -> needs_aneg = true
> 	-> phy_restart_aneg()
> 	-> queue_delayed_work_sync()
> -> phydev->adjust_link = NULL
> -> phy_deatch() -> boom
> 
> Can you confirm whether the driver you are using does call phy_stop()
> prior to phy_disconnect()? 

There is no call to phy_stop().

I can add this to the ethernet drivers, but I wonder if it should be 
called by the code code when doing phy_disconnect(), if it was not 
already stopped.

> If that is the case then this whole theory
> falls apart, if not, then this needs fixing in both the driver and PHYLIB.
> 
> Thanks
>