lkml.org 
[lkml]   [2019]   [Feb]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v2 12/28] thunderbolt: Add functions for allocating and releasing hop IDs
    On Tue, Feb 12, 2019 at 01:59:27PM +0100, Lukas Wunner wrote:
    > On Tue, Feb 12, 2019 at 02:51:25PM +0200, Mika Westerberg wrote:
    > > On Tue, Feb 12, 2019 at 01:43:33PM +0100, Lukas Wunner wrote:
    > > > On Mon, Feb 11, 2019 at 10:30:43AM +0200, Mika Westerberg wrote:
    > > > > On Sun, Feb 10, 2019 at 01:13:53PM +0100, Lukas Wunner wrote:
    > > > > > If there are two Macs at the ends of the daisy-chain with Thunderbolt
    > > > > > devices in-between, the other Mac may already have established tunnels
    > > > > > to some of the devices and therefore has occupied hop entries in the
    > > > > > devices' path config space. How do you ensure that you don't allocate
    > > > > > the same entries and overwrite the other Mac's hop entries, thereby
    > > > > > breaking its tunnels?
    > > > >
    > > > > If the other Mac has enumerated the device (set the upstream port,
    > > > > route, depth) then the other Mac cannot access the device. You get an
    > > > > error (we deal with that in the later patch in the series when we
    > > > > identify XDomain connections). The Hop ID allocation is only relevant in
    > > > > a single domain. Crossing one needs to have protocol such as we have in
    > > > > case of ThunderboltIP to negotiate Hop IDs used in the link between two
    > > > > domains.
    > > >
    > > > Understood now, thanks. (Well, in part at least.)
    > > >
    > > > It looks like there's a race condition currently in tb_switch_configure()
    > > > wherein two machines on the daisy chain may write the config simultaneously
    > > > and overwrite each other's changes. Isn't there some kind of synchonization
    > > > mechanism available to prevent such an outcome?
    > >
    > > AFAICT that's expected. The host that first enumerated the device wins.
    >
    > Yes but tb_switch_configure() goes on to blindly call
    > tb_plug_events_active(). Does that or any other subsequently called
    > function fail if another machine managed to overwrite the switch config?

    Yes, once the switch is enumerated the other domain cannot access it
    anymore but instead gets back errors.

    \
     
     \ /
      Last update: 2019-02-12 14:03    [W:7.614 / U:0.524 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site