On Thu, 10 Oct 2019 10:55:15 -0400
Steven Rostedt <rost...@goodmis.org> wrote:
I'll try to add more detail (mapping to functions)
>
> OK, so basically this moves the enabling of function tracing from
> within the ftrace_module_enable() code without releasing the
> ftrace_lock mutex.
>
> But we have an issue with the state of the module here, as it is still
> set as MODULE_STATE_UNFORMED. Let's look at what happens if we have:
>
>
> CPU0 CPU1
> ---- ----
> echo function > current_tracer
Just need to know that the above will now have all loaded modules have
their functions being traced. That is ftrace_startup > 0.
> modprobe foo
> enable foo functions to be traced
> (foo function records not disabled)
In your code, we have here:
load_module()
foo->state == UNFORMED
ftrace_module_init()
ftrace_process_locs()
mutex_lock(ftrace_lock);
__ftrace_replace_code(rec, 1)
/* Enabling foo's functions */
mutex_unlock(ftrace_lock);
> echo nop > current_tracer
>
> disable all functions being
> traced including foo functions
ftrace_shutdown()
ftrace_run_update_code()
ftrace_arch_code_modify_prepare()
[ on arm and nds32 ]
>
> arch calls set_all_modules_text_rw()
> [skips UNFORMED modules, which foo still is ]
>
> set foo's text to read-only
> foo's state to COMING
complete_formation()
module_enable_ro()
>
> tries to disable foo's functions
> foo's text is read-only
arch_ftrace_update_code()
ftrace_modify_all_code()
[ Includes foo's functions ]
>
> BUG trying to write to ro text!!!
Hope that makes more sense.
-- Steve
>
>
> Like I said, this is very subtle. It may no longer be a bug on x86
> with your patches, but it will bug on ARM or anything else that still
> uses set_all_modules_text_rw() in the ftrace prepare code.
