On Fri, 2020-08-21 at 10:42 +0800, Nicolas Boichat wrote: > On Fri, Aug 21, 2020 at 10:36 AM Joe Perches <joe@xxxxxxxxxxx> wrote: > > On Thu, 2020-08-20 at 21:57 -0400, Steven Rostedt wrote: > > > On Fri, 21 Aug 2020 09:39:19 +0800 > > > Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote: > > [] > > > > 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. > > > > Why? > > > > I don't see much value in a trace_printk checkpatch warning. > > tracing is still dependent on CONFIG_TRACING otherwise > > trace_printk is an if (0) > > > > ELI5 please. > > This is my "new" canned answer to this: > > Please do not use trace_printk in production code [1,2], it is only > meant for debug use. Consider using trace events, or dev_dbg. > [1] https://elixir.bootlin.com/linux/v5.8/source/kernel/trace/trace.c#L3158 > [2] https://elixir.bootlin.com/linux/v5.8/source/include/linux/kernel.h#L766 > > I also had arguments in patch 2/3 notes: > > There's at least 3 reasons that I can come up with: > 1. trace_printk introduces some overhead. [some users, e.g. > Android/Chrome OS, want CONFIG_TRACING but _not_ that extra overhead] > 2. If the kernel keeps adding always-enabled trace_printk, it will be > much harder for developers to make use of trace_printk for debugging. > 3. People may assume that trace_printk is for debugging only, and may > accidentally output sensitive data (theoretical at this stage). Perhaps make trace_printk dependent on #define DEBUG? Something like: --- include/linux/kernel.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 500def620d8f..6ca8f958df73 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -717,6 +717,7 @@ do { \ * let gcc optimize the rest. */ +#ifdef DEBUG #define trace_printk(fmt, ...) \ do { \ char _______STR[] = __stringify((__VA_ARGS__)); \ @@ -725,6 +726,12 @@ do { \ else \ trace_puts(fmt); \ } while (0) +#else +#define trace_printk(fmt, ...) \ +do { \ + __trace_printk_check_format(fmt, ##args); \ +} while (0) +#endif #define do_trace_printk(fmt, args...) \ do { \
