On 14/01/2020 20:33, Dmitry Osipenko wrote: > 14.01.2020 18:09, Jon Hunter пишет: >> >> On 12/01/2020 17:29, Dmitry Osipenko wrote: >>> I was doing some experiments with I2C and noticed that Tegra APB DMA >>> driver crashes sometime after I2C DMA transfer termination. The crash >>> happens because tegra_dma_terminate_all() bails out immediately if pending >>> list is empty, thus it doesn't release the half-completed descriptors >>> which are getting re-used before ISR tasklet kicks-in. >> >> Can you elaborate a bit more on how these are getting re-used? What is >> the sequence of events which results in the panic? I believe that this >> was also reported in the past [0] and so I don't doubt there is an issue >> here, but would like to completely understand this. >> >> Thanks! >> Jon >> >> [0] https://lore.kernel.org/patchwork/patch/675349/ >> > > In my case it happens in the touchscreen driver during of the > touchscreen's interrupt handling (in a threaded IRQ handler) + CPU is > under load and there is other interrupts activity. So what happens here > is that the TS driver issues one I2C transfer, which fails with > (apparently bogus) timeout (because DMA descriptor is completed and > removed from the pending list, but tasklet not executed yet), and then > TS immediately issues another I2C transfer that re-uses the > yet-incompleted descriptor. That's my understanding. OK, but what is the exact sequence that it allowing it to re-use the incompleted descriptor? Thanks Jon -- nvpublic
