Re: [PATCH] riscv: ftrace: no need to acquire text_mutex when executed in stop_machine

[Changbin Du]

On Thu, Mar 10, 2022 at 09:27:42AM -0500, Steven Rostedt wrote:
> On Thu, 10 Mar 2022 12:54:54 +0800
> Changbin Du <changbin.du@xxxxxxxxx> wrote:
> 
> > It's safe to patch text segment in stop_machine. No race is possible here.
> > Besides, there is a false positive for the lock assertion in
> > patch_insn_write() since the lock is not held by cpu migration thread.
> > 
> > So we actually don't need our ftrace_arch_code_modify_prepare/post(). And
> > the lock assertion in patch_insn_write() should be removed to avoid
> > producing lots of false positive warnings.
> > 
> > Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx>
> 
> Ideally, RISC-V should try to get off of the stop_machine approach, and
> move to the breakpoint modification.
>
yes, that's a further step. I can feel a obvious stall to enable ftrace running
in QEMU. (maybe qemu-riscv tcg is too slow...)

> -- Steve

-- 
Cheers,
Changbin Du