Date: Thu, 24 Aug 2006 23:26:21 +0400 From: Oleg Bulyzhin <oleg@freebsd.org> To: Pyun YongHyeon <pyunyh@gmail.com> Cc: Michael Reifenberger <mike@Reifenberger.com>, freebsd-current@freebsd.org Subject: Re: call for bge(4) testers Message-ID: <20060824192621.GB39797@lath.rinet.ru> In-Reply-To: <20060824014121.GE22634@cdnetworks.co.kr> References: <20060822073201.GI12848@cdnetworks.co.kr> <20060822144341.L5561@fw.reifenberger.com> <20060822204342.GA4943@lath.rinet.ru> <20060823005554.GC17902@cdnetworks.co.kr> <20060823124035.GA18628@lath.rinet.ru> <20060824002632.GA22634@cdnetworks.co.kr> <20060824004225.GB25876@lath.rinet.ru> <20060824011116.GD22634@cdnetworks.co.kr> <20060824012450.GC27699@lath.rinet.ru> <20060824014121.GE22634@cdnetworks.co.kr>
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On Thu, Aug 24, 2006 at 10:41:21AM +0900, Pyun YongHyeon wrote: > On Thu, Aug 24, 2006 at 05:24:50AM +0400, Oleg Bulyzhin wrote: > > On Thu, Aug 24, 2006 at 10:11:16AM +0900, Pyun YongHyeon wrote: > > > On Thu, Aug 24, 2006 at 04:42:25AM +0400, Oleg Bulyzhin wrote: > > > > On Thu, Aug 24, 2006 at 09:26:32AM +0900, Pyun YongHyeon wrote: > > > > > On Wed, Aug 23, 2006 at 04:40:35PM +0400, Oleg Bulyzhin wrote: > > > > > > [...] > > > > > > > > > > > > > > My idea was: perhaps, under certain condition, concurrent access to PHY could > > > > > > lead to hardware deadlock. > > > > > > > > > > > > > > > > Yes. Because MII bus access needs several steps to access PHY > > > > > registers its operation shouldn't be interrupted until all pending > > > > > requests are served. > > > > > > > > > > I can't sure you remember my mail for MII lock which modifies > > > > > mii_phy_probe API to take an additional mutex. The driver mutex > > > > > could be used with MII bus access/callbacks. > > > > > > > > Yes, i remember that mail but i didnt had time to dig code deep enough > > > > to give an answer. I did it recently, while working on PR. > > > > > > > > > > Glad to hear that. :-) > > > > > > > > If interface is up/running and auto negotiation is in progress MII > > > > > layer would inspect BMSR register periodically to know the state > > > > > of link. During the time if you run ifconfig(8) to know the state > > > > > of the link or to change media type/duplex it will access PHY > > > > > registers. Normally it would end up with "link states coalesced" > > > > > messages. > > > > > > > > > > As you know the two callbacks(vge_ifmedia_upd/vge_ifmedia_sts) will > > > > > end up with calling mii_mediachg() or mii_pollstat() which in turn > > > > > access PHY registers. So if MII access is properly serialized we > > > > > wouldn't get stale data. I guess your fix solves it by protecting > > > > > callbacks with driver mutex but it wouldn't fix other cases. > > > > > For example see vge_miibus_statchg MII interface. > > > > > > > > MII layer does not have it's own callouts, i.e. those autonegotiation > > > > checks of BMSR are triggered by driver's _tick() function, which are locked. > > > > So if we have locked _tick() & _ifmedia_(upd|sts) functions, concurrent > > > > access to PHY is impossible. > > > > (If we are talking about vge_miibus_statchg(), it would be: > > > > vge_tick (here we obtain lock) -> mii_tick -> ciphy_service -> > > > > mii_phy_update -> vge_miibus_statchg). > > > > > > > > > > If we set media type manually while autonegotiation is in progress, > > > wouldn't it access PHY registers without driver lock? > > > > No (if we have _tick() & ifmedia callbacks locked): > > ioctl -> netioctl -> ifhwioctl -> vge_ioctl(SIOCSIFMEDIA) -> ifmedia_ioctl -> > > vge_ifmedia_upd (here we obtain lock) -> mii_mediachg -> > > ciphy_service(MII_MEDIACHG) -> mii_phy_update -> vge_miibus_statchg > > > > Ah...I've missed the your assumption ifmedia callbacks were locked. > As you said, several drivers don't have locks for ifmedia callback > handlers. These drivers would access PHY registers without locks. I believe all such drivers should be fixed. > > -- > Regards, > Pyun YongHyeon -- Oleg.
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