On Mon, Dec 14, 2020 at 09:43:25AM -0500, Alberto Sentieri wrote: > Alan, > > I was finally able to assemble (on my desk) a similar environment which can > reproduce the problem. It is locking with only 18 USB devices, which are > being accessed in higher frequency than on the regular application (once > every 3 seconds instead of once every 15 seconds). I was able to reproduce > locks with kernel version 5.9.8, which I compiled myself. > > Now a brief description of what I did. > > Each access I referred to on the first paragraph was composed of 3 64-byte > USB interrupt packets, which are: a request the computer sends, a response > the device sends back, and a confirmation that the computer send to finish > the cycle, which would be repeated in about 3 seconds. > > The computer motherboard I am using has a UART (apparently a 16550) and I > could enable a serial console using: console=tty1 console=ttyS0,115200. I > also would like to point out that ipv6.disable=1 is the other kernel > argument I am using. The serial console was working properly and all its > output was being captured by another computer during the locks. My lab > machine has the same USB expansion card model being used at the production > environment and that was the one being used during the experiments. Though > my lab machine has some extra PCI USB cards installed, they were not being > using during the locks. > > I did the experiment just a few times during the weekend, after receiving > the last parts I needed on Saturday. > > So, with kernel 5.4.0-53-generic, which is one of the kernels released with > Ubuntu, the locked happened in just a couple of minutes. I tried that twice. > With kernel 5.9.8, the lock took more time to happen. Initially I though it > would not happen, because I'd observed the machine running for about 15 > minutes and everything seemed normal. However after a couple of hours I > found the machine locked. I also would like to point out that I’ve been > using this machine for more than 6 months and that it had never locked on > me, so that excludes any hardware problem. > > Unfortunately on the 3 times it locked (2 with 5.4.0 and one with 5.9.8) > nothing was printed on the serial console. > > I will be working on this during the day and I will try to enable some of > the debugging tools you suggested in your previous emails. > > Any comment on this will be highly appreciated. We'll have to wait and see what the tests and debugging tools reveal. As for the comment about the hardware being reliable -- in fact, you can't be certain of this. It may be that your test is stressing the hardware in a way that it never experienced during the prior six months. Alan Stern
