Re: [PATCH v4] riscv: patch: Fixup lockdep warning in stop_machine

[Björn Töpel]

Changbin Du <changbin.du@xxxxxxxxxx> writes:

> On Wed, Feb 15, 2023 at 09:24:33AM +0800, Guo Ren wrote:
>> On Wed, Feb 15, 2023 at 8:22 AM Conor Dooley <conor@xxxxxxxxxx> wrote:
>> >
>> > Hey Changbin,
>> >
>> > On Thu, Feb 02, 2023 at 07:41:16PM +0800, Changbin Du wrote:
>> > > The task of ftrace_arch_code_modify(_post)_prepare() caller is
>> > > stop_machine, whose caller and work thread are of different tasks. The
>> > > lockdep checker needs the same task context, or it's wrong. That means
>> > > it's a bug here to use lockdep_assert_held because we don't guarantee
>> > > the same task context.
>> I'm trying to delete all stop_machine in riscv, from ftrace to kprobe.
>> When I have done, we needn't this patch.
>>
> Which approch would you use? I looked through the riscv-spec, but didn't find any
> description abount concurrent modification and execution.

CMODX is not specified for RISC-V yet, unfortunately.

This has been discussed here [1]. Maybe we can start with stating for
which implementations Guo's approach work?

[1] https://lore.kernel.org/all/CAJF2gTS0s4X_uwLaEeSqKAyRmxCR2vxRuHhz7-SP2w4bBqzr+Q@xxxxxxxxxxxxxx/