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Date: Fri, 05 Sep 2014 00:40:02 +0100 From: Nix <nix@...eri.org.uk> To: Oliver Neukum <oliver@...kum.org> Cc: linux-kernel@...r.kernel.org Subject: Re: [3.16.1 REGRESSION]: Simtec Entropy Key (cdc-acm) broken in 3.16 On 1 Sep 2014, Oliver Neukum stated: > >> I'll do a bisection of the cdc-acm changes since 3.15 tomorrow night and >> see if I can find the commit at fault. > > Thank you for the report. Please let me know the results of your > bisection. Bisection underway (fifth attempt -- I *may* have characterized it well enough after a few hours of thrashing at it to bisect accurately this time). Some more random info. btw, when the Entropy Key has ended up in a messed up state due to this bug, we sometimes see [ 2.330158] usb 2-1: new full-speed USB device number 2 using ohci-pci [ 2.552465] usb 2-1: device descriptor read/64, error -62 [ 2.870142] usb 2-1: device descriptor read/64, error -62 [ 3.190150] usb 2-1: new full-speed USB device number 3 using ohci-pci [ 3.410137] usb 2-1: device descriptor read/64, error -62 [ 3.740142] usb 2-1: device descriptor read/64, error -62 [ 4.060146] usb 2-1: new full-speed USB device number 4 using ohci-pci [ 4.520133] usb 2-1: device not accepting address 4, error -62 [ 4.730139] usb 2-1: new full-speed USB device number 5 using ohci-pci [ 5.180117] usb 2-1: device not accepting address 5, error -62 [ 5.215194] hub 2-0:1.0: unable to enumerate USB device on port 1 when starting up a working kernel (the key then doesn't work until physically disconnected and reconnected again). More generally, the problem may be at *shutdown* -- something goes wrong during link suspension or something, such that the link never comes up again until physically reconnected. So a straight bisect is misleading -- the error may have been in the *last* kernel tested -- and even then, some kernels (e.g. the 3.15.0 merge base) appear capable of making it work fine. But even this is not consistent: sometimes a kernel that works fine if you repeatedly reboot it (such as 3.15) malfunctions when you reboot into 3.16 -- but sometimes a newly plugged USB key on a 3.16 kernel malfunctions upon reboot, even if you reboot into a working kernel such as 3.15 (and it then proceeds to work indefinitely if you unplug and replug it and stick with 3.15.x, but upon rebooting into 3.16.x it goes wrong again). So sometimes a faulty kernel makes the key go wrong when you restart into another kernel (faulty or not), and sometimes it makes a key go wrong when it is restarted into. There doesn't seem to be any consistency to this that I've spotted, at least not yet. Upon physical reconnection, the USB key works again, even on afflicted kernels. I'm working around this confusing morass by rebooting into each test kernel, unplugging and replugging the entropy key if it was fubared, then rebooting into the same kernel again and seeing if it was still fubared. But this is not terribly fast, particularly not on a headless compact-flash-based Geode box which doesn't even complete booting without the entropy source which this bug cuts off :) so it'll be sometime tomorrow before I can get this bisection done, I'm afraid. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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