On Mon, 20 Aug 2018 15:36:47 +0100 Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote: > On 08/20/2018 03:22 PM, Kim Phillips wrote: > > On Mon, 20 Aug 2018 11:03:03 +0100 > > Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote: > > > >> On 08/16/2018 08:28 PM, Mathieu Poirier wrote: > >>> On Wed, 15 Aug 2018 at 09:28, Kim Phillips <kim.phillips@xxxxxxx> wrote: > >>>> > >>>> On Wed, 15 Aug 2018 10:39:13 +0100 > >>>> Will Deacon <will.deacon@xxxxxxx> wrote: > >>>> > >>>>> On Tue, Aug 14, 2018 at 01:42:27PM -0600, Mathieu Poirier wrote: > >>>>>> On Tue, 14 Aug 2018 at 11:09, Kim Phillips <kim.phillips@xxxxxxx> wrote: > >>>>>>> The other thing that's going on here is that I'm becoming numb to the > >>>>>>> loathsome "failed to mmap with 12 (Cannot allocate memory)" being > >>>>>>> returned no matter what the error is/was. E.g., an error that would > >>>>>>> indicate a sense of non-implementation would be much better > >>>>>>> appreciated than presumably what the above is doing, i.e., returning > >>>>>>> -ENOMEM. That, backed up with specific details in the form of human > >>>>>>> readable text in dmesg would be *most* welcome. > >>>>>> > >>>>>> As part of the refactoring of the code to support CPU-wide scenarios I > >>>>>> intend to emit better diagnostic messages from the driver. Modifying > >>>>>> rb_alloc_aux() to propagate the error message generated by the > >>>>>> architecture specific PMUs doesn't look hard either and I _may_ get to > >>>>>> it as part of this work. > >>>>> > >>>>> For the record, I will continue to oppose PMU drivers that dump diagnostics > >>>>> about user-controlled input into dmesg, but the coresight drivers are yours > >>>>> so it's up to you and I won't get in the way! > >>>> > >>>> That sounds technically self-contradicting to me. Why shouldn't > >>>> coresight share the same policies as those used for PMU drivers? Or > >>>> why not allow the individual vendor PMU driver authors control the > >>>> level of user-friendliness of their own drivers? > >>>> > >>>> That being said, Matheiu, would you accept patches that make coresight > >>>> more verbose in dmesg? > >>> > >>> It depends on the issue you're hoping to address. I'd rather see the > >>> root cause of the problem fixed than adding temporary code. Suzuki > >>> added the ETR perf API and I'm currently working on CPU-wide > >>> scenarios. From there and with regards to what can happen in > >>> setup_aux(), we should have things covered. > >> > >> I think the main issue is the lack of error code propagation from > >> setup_aux() back to the perf_aux_output_handle_begin(), which always > >> return -ENOMEM. If we fix that, we could get better idea of whats > >> wrong. > > > > Why get a better idea when we can get the exact details? > > The different values for error numbers are there for a reason... But the same error number, e.g., EINVAL, can be returned for different reasons. > >> If someone is planning to add verbose messages, they may do so by adding > >> dev_dbg() / pr_debug(), which can be turned on as and when needed. > > > > I disagree: that just adds another usage and kernel configuration > > obstacle. Why not use pr_err straight up? > > I personally don't agree to usage of pr_err() in paths which are easily > triggered from user input. Why not? pr_* are ratelimited. > Also, we are moving all the "debugging" > messages to the dynamic debug, to prevent lockdep splats. Are you referring to this?: https://lkml.org/lkml/2018/5/1/73 Re-reading the thread, AFAICT, it was never proven that the splats occurred due to the dev_infos, and there's no dev_info in this stacktrace: https://lkml.org/lkml/2018/5/10/269 But even if it were, wouldn't the splats also occur with dev_dbg? Kim
