From: David Daney <ddaney@caviumnetworks.com>
To: Florian Fainelli <f.fainelli@gmail.com>, Mason <slash.tmp@free.fr>
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: Wed, 6 Sep 2017 13:49:41 -0700 [thread overview]
Message-ID: <6890a27f-e87e-62c1-a676-e5ddf968adb6@caviumnetworks.com> (raw)
In-Reply-To: <572f49fd-f623-f064-a551-e243c57cef7f@gmail.com>
On 09/06/2017 11:59 AM, Florian Fainelli wrote:
> On 09/06/2017 11:00 AM, David Daney wrote:
>> On 08/31/2017 11:29 AM, Florian Fainelli wrote:
>>> On 08/31/2017 11:12 AM, Mason wrote:
>>>> 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.
>>>
>>> Actually you are right, once phydev->link is set to 0 these would become
>>> no-ops. Still scratching my head as to what happens for David then...
>>>
>>>>
>>>> Also, queue_delayed_work() is only called in polling mode.
>>>> David stated that he's using interrupt mode.
>>
>> Did you see what I wrote?
>
> Still not following, see below.
>
>>
>> phy_disconnect() calls phy_stop_interrupts() which puts it into polling
>> mode. So the polling work gets queued unconditionally.
>
> What part of phy_stop_interrupts() is responsible for changing
> phydev->irq to PHY_POLL? free_irq() cannot touch phydev->irq otherwise
> subsequent request_irq() calls won't work anymore.
> phy_disable_interrupts() only calls back into the PHY driver to
> acknowledge and clear interrupts.
>
> If we were using a PHY with PHY_POLL, as Marc said, the first
> synchronous call to phy_state_machine() would have acted on PHY_HALTED
> and even if we incorrectly keep re-scheduling the state machine from
> PHY_HALTED to PHY_HALTED the second time around nothing can happen.
>
> What are we missing here?
>
OK, I am now as confused as you guys are. I will go back and get an
ftrace log out of the failure.
David.
next prev parent reply other threads:[~2017-09-06 20:49 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=6890a27f-e87e-62c1-a676-e5ddf968adb6@caviumnetworks.com \
--to=ddaney@caviumnetworks.com \
--cc=andrew@lunn.ch \
--cc=davem@davemloft.net \
--cc=f.fainelli@gmail.com \
--cc=geert+renesas@glider.be \
--cc=mans@mansr.com \
--cc=marc_gonzalez@sigmadesigns.com \
--cc=netdev@vger.kernel.org \
--cc=slash.tmp@free.fr \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).