On Fri, 21 Aug 2020 09:39:19 +0800 Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote: > On Fri, Aug 21, 2020 at 8:36 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > On Fri, 21 Aug 2020 08:13:00 +0800 > > Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote: > > > > > On Thu, Aug 20, 2020 at 10:23 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > > > > > On Thu, 20 Aug 2020 17:14:12 +0800 > > > > Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote: > > > > > > > > > Technically, we could only initialize the trace_printk buffers > > > > > when the print env is switched, to avoid the build error and > > > > > unconditional boot-time warning, but I assume this printing > > > > > framework will eventually get removed when the driver moves out > > > > > of staging? > > > > > > > > Perhaps this should be converting into a trace event. Look at what bpf > > > > did for their bpf_trace_printk(). > > > > > > > > The more I think about it, the less I like this series. > > > > > > To make it clear, the primary goal of this series is to get rid of > > > trace_printk sprinkled in the kernel by making sure some randconfig > > > builds fail. Since my v2, there already has been one more added (the > > > one that this patch removes), so I'd like to land 2/3 ASAP to prevent > > > even more from being added. > > > > > > Looking at your reply on 1/3, I think we are aligned on that goal? Is > > > there some other approach you'd recommend? > > > > > > Now, I'm not pretending my fixes are the best possible ones, but I > > > would much rather have the burden of converting to trace events on the > > > respective driver maintainers. (btw is there a short > > > documentation/tutorial that I could link to in these patches, to help > > > developers understand what is the recommended way now?) > > > > > > > I like the goal, but I guess I never articulated the problem I have > > with the methodology. > > > > trace_printk() is meant to be a debugging tool. Something that people > > can and do sprinkle all over the kernel to help them find a bug in > > areas that are called quite often (where printk() is way too slow). > > > > The last thing I want them to deal with is adding a trace_printk() with > > their distro's config (or a config from someone that triggered the bug) > > only to have the build to fail, because they also need to add a config > > value. > > > > I add to the Cc a few developers I know that use trace_printk() in this > > fashion. I'd like to hear their view on having to add a config option > > to make trace_printk work before they test a config that is sent to > > them. > > Gotcha, thanks. I have also used trace_printk in the past, as > uncommitted changes (and understand the usefulness ,-)). And in Chrome > OS team here, developers have also raised this concern: how do we make > the developer flow convenient so that we can add trace_printk to our > code for debugging, without having to flip back that config option, > and _yet_ make sure that no trace_printk ever makes it into our > production kernels. We have creative ways of making that work (portage > USE flags and stuff). But I'm not sure about other flows, and your > concern is totally valid... > > Some other approaches/ideas: > 1. Filter all lkml messages that contain trace_printk. Already found > 1 instance, and I can easily reply to those with a semi-canned answer, > if I remember to check that filter regularly (not sustainable in the > long run...). Added Joe Perches to the thread. We can update checkpatch.pl to complain about a trace_printk() that it finds in the added code. > 2. Integration into some kernel test robot? (I will not roll my own > for this ,-)) It may be a bit difficult as some debug config options > do enable trace_printk, and that's ok. > 3. In Chromium OS, I can add a unit test (i.e. something outside of > the normal kernel build system), but that'll only catch regressions > downstream (or when we happen to backport patches). > > Down the line, #3 catches what I care about the most (Chromium OS > issues: we had production kernels for a few days/weeks showing that > splat on boot), but it'd be nice to have something upstream that > benefits everyone. > What about an opposite config. That is, not have a config to enable it. But one to disable it. If it is disabled and a trace_printk is found, it will fail the build. This way your builds will not allow your kernel to get out the door with one. #ifdef CONFIG_DISABLE_TRACE_PRINTK #define trace_printk __this_function_is_disabled #endif ? -- Steve
