On 01/04/2017 10:44 PM, Florian Fainelli wrote: > On 01/04/2017 08:10 AM, Zefir Kurtisi wrote: >> On 01/04/2017 04:30 PM, Florian Fainelli wrote: >>> >>> >>> On 01/04/2017 07:27 AM, Zefir Kurtisi wrote: >>>> On 01/04/2017 04:13 PM, Florian Fainelli wrote: >>>>> >>>>> >>>>> On 01/04/2017 07:04 AM, Zefir Kurtisi wrote: >>>>>> While in RUNNING state, phy_state_machine() checks for link changes by >>>>>> comparing phydev->link before and after calling phy_read_status(). >>>>>> This works as long as it is guaranteed that phydev->link is never >>>>>> changed outside the phy_state_machine(). >>>>>> >>>>>> If in some setups this happens, it causes the state machine to miss >>>>>> a link loss and remain RUNNING despite phydev->link being 0. >>>>>> >>>>>> This has been observed running a dsa setup with a process continuously >>>>>> polling the link states over ethtool each second (SNMPD RFC-1213 >>>>>> agent). Disconnecting the link on a phy followed by a ETHTOOL_GSET >>>>>> causes dsa_slave_get_settings() / dsa_slave_get_link_ksettings() to >>>>>> call phy_read_status() and with that modify the link status - and >>>>>> with that bricking the phy state machine. >>>>> >>>>> That's the interesting part of the analysis, how does this brick the PHY >>>>> state machine? Is the PHY driver changing the link status in the >>>>> read_status callback that it implements? >>>>> >>>> phydev->read_status points to genphy_read_status(), where the first call >>>> goes to >>>> genphy_update_link() which updates the link status. >>>> >>>> Thereafter phy_state_machine():RUNNING won't be able to detect the link >>>> loss >>>> anymore unless the link state changes again. >>>> >>>> >>>> I was trying to figure out if there is a rule that forbids changing >>>> phydev->link >>>> from outside the state machine, but found several places where it happens >>>> (either >>>> directly, or over genphy_read_status() or over genphy_update_link()). >>>> >>>> Curious how this did not show up before, since within the dsa setup it is >>>> very >>>> easy to trigger: >>>> a) physically disconnect link >>>> b) within one second run ethtool ethX >>> >>> You need to be more specific here about what "the dsa setup" is, drivers >>> involved, which ports of the switch you are seeing this with (user >>> facing, CPU port, DSA port?) etc. >>> >> I am working on top of LEDE and with that at kernel 4.4.21 - alas I checked >> the >> related source files and believe the effect should be reproducible with HEAD. >> >> The setup is as follows: >> mv88e6321: >> * ports 0+1 connected to fibre-optics transceivers at fixed 100 Mbps >> * port 4 is CPU port >> * custom phy driver (replacement for marvell.ko) only populated with >> * .config_init to >> * set fixed speed for ports 0+1 (when in FO mode) >> * run genphy_config_init() for all other modes (here: CPU port) >> * .config_aneg=genphy_config_aneg, .read_status=genphy_read_status >> >> >> To my understanding, the exact setup is irrelevant - to reproduce the issue >> it is >> enough to have a means of running genphy_update_link() (as done in e.g. >> mediatek/mtk_eth_soc.c, dsa/slave.c), or genphy_read_status() (as done in >> e.g. >> hisilicon/hns/hns_enet.c) or phy_read_status() (as done in e.g. >> ethernet/ti/netcp_ethss.c, ethernet/aeroflex/greth.c, etc.). In the observed >> drivers it is mostly implemented in the ETHTOOL_GSET execution path. >> >> Once you get the link state updated outside the phy state machine, it >> remains in >> invalid RUNNING. To prevent that invalid state, to my understanding upper >> layer >> drivers (Ethernet, dsa) must not modify link-states in any case (including >> calling >> the functions noted above), or we need the proposed fail-safe mechanism to >> prevent >> getting stuck. > > OK, I see the code path involved now, sorry -ENOCOFFEE when I initially > responded. Yes, clearly, we should not be mangling the PHY device's link > by calling genphy_read_status(). At first glance, none of the users > below should be doing what they are doing, but let's kick a separate > patch series to collect feedback from the driver writes. > > Thanks! > Ok, thanks for taking time.
The kbuild test robot error is due to 'struct device dev' been removed from phy_device struct since 4.4.21. Does it make sense to provide a v2 fixing that, or do you expect that this fail-safe mechanism is not needed once all Ethernet/dsa drivers are fixed? I think it won't hurt to add the check simply to ensure that it got fixed and the issue is not popping up thereafter. Cheers, Zefir
