On Wed, Jul 8, 2020 at 1:02 AM Steven Rostedt [off-list ref] wrote:

On Tue,  7 Jul 2020 18:21:17 +0900
Masahiro Yamada [off-list ref] wrote:

quoted

  ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)

exists here in sub-directories of lib/ to keep the behavior of
commit 2464a609ded0 ("ftrace: do not trace library functions").

Since that commit, not only the objects in lib/ but also the ones in
the sub-directories are excluded from ftrace (although the commit
description did not explicitly mention this).

However, most of library functions in sub-directories are not so hot.
Re-add them to ftrace.

I'm OK with this change, but note, it wasn't just the hot path that I
disabled ftrace on lib for, but some of these calls are done very early
at boot up. It may have been PowerPC that I was stumbling over. The
issue is that they would call mcount before the kernel was mapped
properly, and the system would crash.

My PowerPC box no longer boots so I can't test this anymore. But a lot
has changed since 2008, and all this may very well be OK.

-- Steve

That's why I split this into two commits
so that we can do git-bisect and
revert the second one in case of a regression.

Anyway, we have some more time to test this in linux-next
(and somebody reports an issue, if any).


-- 
Best Regards
Masahiro Yamada