Hi Andy On Fri, Aug 23, 2024 at 04:21:24PM +0300, Andy Shevchenko wrote: > On Fri, Aug 23, 2024 at 12:48 PM Serge Semin <fancer.lancer@xxxxxxxxx> wrote: > > > > Hi folks > > > > Any comments or suggestion about the change? The kernel occasionally > > _deadlocks_ without it for the DW UART + DW DMAC hardware setup. > > I have no time to look at that, but FWIW with a stress tests on older > machines I have seen something similar from time to time (less than > 10% reproducibility ration IIRC). Thanks for the response. I also used to have the system hanging up at the very rare occasion, but after I decreased the size of the Rx DMA-buffer (to fix a platform-specific problem) and sped up the port the deadlock probability dramatically increased so I managed to debug the hanging ups. > > P.S. Is there is any possibility to have a step-by-step reproducer? There is a good chance that my approach might be platform-specific (but the problem is general for sure), but here is what I did to make the deadlock reproducible at the reasonable time: 1. Revert the patch in the subject (if it's applied) 2. Decrease the Rx DMA-buffer size: drivers/tty/serial/8250/8250_dma.c: dma->rx_size = SZ_512; 3. Increase the serial communication baud-rate: stty -F /dev/ttyS1 1500000 raw -echo -echok -echoe; 4. Loopback the ttyS1 interface: connect Tx and Rx pins. 5. Start pushing data to the ttS1 interface by the chunks someway greater than 512 bytes. Like this: while :; do echo -n "-"; head -c 65536 /dev/zero > /dev/ttyS1; done In my case the system almost always hangs up after 10-50-100-200 iterations of the one-liner above. > Also can we utilise (and update if needed) the open source project > https://github.com/cbrake/linux-serial-test? I guess the utility can be used to reproduce the problem, but the data integrity check wasn't required in my case. I am also not sure whether the loopback-test is required to reproduce the denoted deadlock, since only the Rx code-path causes it. So most likely the heavy inbound traffic shall be enough. -Serge(y) > > -- > With Best Regards, > Andy Shevchenko
