lkml.org 
[lkml]   [2023]   [Oct]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRE: [PATCH v3 5/5] r8152: Block future register access if register access fails
    Date
    Doug Anderson <dianders@chromium.org>
    > Sent: Tuesday, October 17, 2023 10:17 PM
    [...]
    > > That is, the loop would be broken when the fail rate of the control transfer is high or low enough.
    > > Otherwise, you would queue a usb reset again and again.
    > > For example, if the fail rate of the control transfer is 10% ~ 60%,
    > > I think you have high probability to keep the loop continually.
    > > Would it never happen?
    >
    > Actually, even with a failure rate of 10% I don't think you'll end up
    > with a fully continuous loop, right? All you need is to get 3 failures
    > in a row in rtl8152_get_version() to get out of the loop. So with a
    > 10% failure rate you'd unbind/bind 1000 times (on average) and then
    > (finally) give up. With a 50% failure rate I think you'd only
    > unbind/bind 8 times on average, right? Of course, I guess 1000 loops
    > is pretty close to infinite.
    >
    > In any case, we haven't actually seen hardware that fails like this.
    > We've seen failure rates that are much much lower and we can imagine
    > failure rates that are 100% if we're got really broken hardware. Do
    > you think cases where failure rates are middle-of-the-road are likely?

    That is my question, too.
    I don't know if something would cause the situation, either.
    This is out of my knowledge.
    I am waiting for the professional answers, too.

    A lot of reasons may cause the fail of the control transfer.
    I don't have all of the real situation to analyze them.
    Therefore, what I could do is to assume different situations.
    You could say my hypotheses are unreasonable.
    However, I have to tell you what I worry.

    > I would also say that nothing we can do can perfectly handle faulty
    > hardware. If we're imagining theoretical hardware, we could imagine
    > theoretical hardware that de-enumerated itself and re-enumerated
    > itself every half second because the firmware on the device crashed or
    > some regulator kept dropping. This faulty hardware would also cause an
    > infinite loop of de-enumeration and re-enumeration, right?
    >
    > Presumably if we get into either case, the user will realize that the
    > hardware isn't working and will unplug it from the system. While the

    Some of our devices are onboard. That is, they couldn't be unplugged.
    That is why I have to consider a lot of situations.

    > system is doing the loop of trying to enumerate the hardware, it will
    > be taking up a bunch of extra CPU cycles but (I believe) it won't be
    > fully locked up or anything. The machine will still function and be
    > able to do non-Ethernet activities, right? I would say that the worst
    > thing about this state would be that it would stress corner cases in
    > the reset of the USB subsystem, possibly ticking bugs.
    >
    > So I guess I would summarize all the above as:
    >
    > If hardware is broken in just the right way then this patch could
    > cause a nearly infinite unbinding/rebinding of the r8152 driver.
    > However:
    >
    > 1. It doesn't seem terribly likely for hardware to be broken in just this way.
    >
    > 2. We haven't seen hardware broken in just this way.
    >
    > 3. Hardware broken in a slightly different way could cause infinite
    > unbinding/rebinding even without this patch.
    >
    > 4. Infinite unbinding/rebinding of a USB adapter isn't great, but not
    > the absolute worst thing.

    It is fine if everyone agrees these.

    Best Regards,
    Hayes

    \
     
     \ /
      Last update: 2023-10-18 13:42    [W:6.702 / U:0.288 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site