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Subject: Re: [PATCH net] net: phy: Run state machine to completion
To: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>,
        "David S. Miller" <davem@davemloft.net>,
        netdev <netdev@vger.kernel.org>
Cc: Russell King <linux@arm.linux.org.uk>, Zach Brown <zach.brown@ni.com>,
        Nathan Sullivan <nathan.sullivan@ni.com>, Andrew Lunn <andrew@lunn.ch>,
        LKML <linux-kernel@vger.kernel.org>, Mason <slash.tmp@free.fr>,
        Mans Rullgard <mans@mansr.com>
References: <20170726192446.32045-1-f.fainelli@gmail.com>
 <69ecff09-3822-31b3-99d2-ebd5ca888e7f@sigmadesigns.com>
From: Florian Fainelli <f.fainelli@gmail.com>
Message-ID: <3f5ee209-1b8e-3616-340b-f26a6e70430d@gmail.com>
Date: Fri, 28 Jul 2017 11:50:52 -0700
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On 07/28/2017 03:57 AM, Marc Gonzalez wrote:
> On 26/07/2017 21:24, Florian Fainelli wrote:
> 
>> Marc reported that he was not getting the PHY library adjust_link()
>> callback function to run when calling phy_stop() + phy_disconnect()
>> which does not indeed happen because we don't make sure we flush the
>> PHYLIB delayed work and let it run to completion. We also need to have
>> a synchronous call to phy_state_machine() in order to have the state
>> machine actually act on PHY_HALTED, set the PHY device's link down, turn
>> the network device's carrier off and finally call the adjust_link()
>> function.
>>
>> Reported-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
>> Fixes: a390d1f379cf ("phylib: convert state_queue work to delayed_work")
>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
>> ---
>> David, this dates back from before the commit mentioned in Fixes but it would
>> be hard to backport to earlier kernels if we flagged the original design flaw
>> that used timers. Also, I am not clear on the timer API whether there was a way
>> to ensure timers would run to completion before they would be cancelled.
>>
>> Marc, please add your Signed-off-by tag since you contributed the second line.
>>
>> Thanks!
>>
>>  drivers/net/phy/phy.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
>> index d0626bf5c540..30e7c43e0d87 100644
>> --- a/drivers/net/phy/phy.c
>> +++ b/drivers/net/phy/phy.c
>> @@ -743,12 +743,17 @@ void phy_trigger_machine(struct phy_device *phydev, bool sync)
>>   */
>>  void phy_stop_machine(struct phy_device *phydev)
>>  {
>> +	/* Run the state machine to completion */
>> +	flush_delayed_work(&phydev->state_queue);
>>  	cancel_delayed_work_sync(&phydev->state_queue);
>>  
>>  	mutex_lock(&phydev->lock);
>>  	if (phydev->state > PHY_UP && phydev->state != PHY_HALTED)
>>  		phydev->state = PHY_UP;
>>  	mutex_unlock(&phydev->lock);
>> +
>> +	/* Now we can run the state machine synchronously */
>> +	phy_state_machine(&phydev->state_queue.work);
> 
> Hello Florian,
> 
> Sorry, I was AFK for a couple of days.
> 
> Thanks for putting the patch together!
> 
> I added dump_stack() at the top of phy_state_machine() to better
> understand what's going on.
> 
> Action: set link down on the command-line
> 
> Results:
> 
> 1) PHY in interrupt mode
> 
> [  136.238889] [<c0378518>] (phy_state_machine) from [<c0378a58>] (phy_stop_machine+0x4c/0x50)
> [  136.247285] [<c0378a58>] (phy_stop_machine) from [<c0379c30>] (phy_disconnect+0x20/0x34)
> [  136.255420] [<c0379c30>] (phy_disconnect) from [<c037d984>] (nb8800_stop+0x84/0xa0)
> [  136.263118] [<c037d984>] (nb8800_stop) from [<c03f52a4>] (__dev_close_many+0x88/0xd0)
> [  136.270989] [<c03f52a4>] (__dev_close_many) from [<c03f540c>] (__dev_close+0x24/0x38)
> [  136.278862] [<c03f540c>] (__dev_close) from [<c03fdd98>] (__dev_change_flags+0x94/0x144)
> [  136.286997] [<c03fdd98>] (__dev_change_flags) from [<c03fde60>] (dev_change_flags+0x18/0x48)
> [  136.295481] [<c03fde60>] (dev_change_flags) from [<c0463350>] (devinet_ioctl+0x6e0/0x7a0)
> [  136.303702] [<c0463350>] (devinet_ioctl) from [<c04657e0>] (inet_ioctl+0x194/0x1c0)
> [  136.311400] [<c04657e0>] (inet_ioctl) from [<c03de2f8>] (sock_ioctl+0x148/0x2fc)
> [  136.318837] [<c03de2f8>] (sock_ioctl) from [<c01dbe80>] (do_vfs_ioctl+0x9c/0x8e8)
> [  136.326361] [<c01dbe80>] (do_vfs_ioctl) from [<c01dc700>] (SyS_ioctl+0x34/0x5c)
> [  136.333710] [<c01dc700>] (SyS_ioctl) from [<c01076c0>] (ret_fast_syscall+0x0/0x3c)
> [  136.341357] nb8800 26000.ethernet eth0: Link is Down
> 
> Above, phy_state_machine() is called synchronously from phy_stop_machine().
> 
> 
> 2) PHY in polling mode
> 
> [   54.045752] CPU: 3 PID: 892 Comm: kworker/3:1 Not tainted 4.13.0-rc1 #7
> [   54.056435] Workqueue: events_power_efficient phy_state_machine
> [   54.085399] [<c0378518>] (phy_state_machine) from [<c012e404>] (process_one_work+0x1d4/0x3ec)
> [   54.093969] [<c012e404>] (process_one_work) from [<c012f250>] (worker_thread+0x268/0x554)
> [   54.102189] [<c012f250>] (worker_thread) from [<c0133fd4>] (kthread+0x108/0x138)
> [   54.109623] [<c0133fd4>] (kthread) from [<c0107778>] (ret_from_fork+0x14/0x3c)
> [   54.116918] nb8800 26000.ethernet eth0: Link is Down
> 
> [   54.122100] CPU: 2 PID: 973 Comm: ip Not tainted 4.13.0-rc1 #7
> [   54.155001] [<c0378518>] (phy_state_machine) from [<c0378a58>] (phy_stop_machine+0x4c/0x50)
> [   54.163397] [<c0378a58>] (phy_stop_machine) from [<c0379c30>] (phy_disconnect+0x20/0x34)
> [   54.171532] [<c0379c30>] (phy_disconnect) from [<c037d984>] (nb8800_stop+0x84/0xa0)
> [   54.179231] [<c037d984>] (nb8800_stop) from [<c03f52a4>] (__dev_close_many+0x88/0xd0)
> [   54.187103] [<c03f52a4>] (__dev_close_many) from [<c03f540c>] (__dev_close+0x24/0x38)
> [   54.194975] [<c03f540c>] (__dev_close) from [<c03fdd98>] (__dev_change_flags+0x94/0x144)
> [   54.203109] [<c03fdd98>] (__dev_change_flags) from [<c03fde60>] (dev_change_flags+0x18/0x48)
> [   54.211594] [<c03fde60>] (dev_change_flags) from [<c0463350>] (devinet_ioctl+0x6e0/0x7a0)
> [   54.219816] [<c0463350>] (devinet_ioctl) from [<c04657e0>] (inet_ioctl+0x194/0x1c0)
> [   54.227513] [<c04657e0>] (inet_ioctl) from [<c03de2f8>] (sock_ioctl+0x148/0x2fc)
> [   54.234950] [<c03de2f8>] (sock_ioctl) from [<c01dbe80>] (do_vfs_ioctl+0x9c/0x8e8)
> [   54.242473] [<c01dbe80>] (do_vfs_ioctl) from [<c01dc700>] (SyS_ioctl+0x34/0x5c)
> [   54.249821] [<c01dc700>] (SyS_ioctl) from [<c01076c0>] (ret_fast_syscall+0x0/0x3c)
> 
> Above() phy_state_machine() is called twice
> - first supposedly after flush_delayed_work() => calls adjust_link()
> - a second time by the explicit call => probably no-op
> 
> Therefore, my reasoning is that flush_delayed_work() is
> unnecessary. The explicit call to phy_state_machine() at
> the end of phy_stop_machine() will handle all cases.
> 
> What do you think?

You are right I also just tested PHY_POLL and PHY_IGNORE_INTERRUPT and
only the synchronous call is necessary. Will re-post a v2 shortly.

> 
> Testing without flush_delayed_work() in polling mode:
> 
> [   58.819100] CPU: 0 PID: 968 Comm: ip Not tainted 4.13.0-rc1 #10
> [   58.852098] [<c0378518>] (phy_state_machine) from [<c0378a50>] (phy_stop_machine+0x44/0x48)
> [   58.860494] [<c0378a50>] (phy_stop_machine) from [<c0379c28>] (phy_disconnect+0x20/0x34)
> [   58.868629] [<c0379c28>] (phy_disconnect) from [<c037d97c>] (nb8800_stop+0x84/0xa0)
> [   58.876328] [<c037d97c>] (nb8800_stop) from [<c03f529c>] (__dev_close_many+0x88/0xd0)
> [   58.884198] [<c03f529c>] (__dev_close_many) from [<c03f5404>] (__dev_close+0x24/0x38)
> [   58.892071] [<c03f5404>] (__dev_close) from [<c03fdd90>] (__dev_change_flags+0x94/0x144)
> [   58.900206] [<c03fdd90>] (__dev_change_flags) from [<c03fde58>] (dev_change_flags+0x18/0x48)
> [   58.908690] [<c03fde58>] (dev_change_flags) from [<c0463348>] (devinet_ioctl+0x6e0/0x7a0)
> [   58.916911] [<c0463348>] (devinet_ioctl) from [<c04657d8>] (inet_ioctl+0x194/0x1c0)
> [   58.924608] [<c04657d8>] (inet_ioctl) from [<c03de2f0>] (sock_ioctl+0x148/0x2fc)
> [   58.932046] [<c03de2f0>] (sock_ioctl) from [<c01dbe80>] (do_vfs_ioctl+0x9c/0x8e8)
> [   58.939569] [<c01dbe80>] (do_vfs_ioctl) from [<c01dc700>] (SyS_ioctl+0x34/0x5c)
> [   58.946917] [<c01dc700>] (SyS_ioctl) from [<c01076c0>] (ret_fast_syscall+0x0/0x3c)
> [   58.954609] nb8800 26000.ethernet eth0: Link is Down
> 
> Above, the call to adjust_link() occurs from the explicit call
> to phy_state_machine()
> 
> Regards.
> 


-- 
Florian