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SubjectRe: [PATCH v5 1/6] kprobes: Remove dependency to the module_mutex
On Fri, Jul 24, 2020 at 11:17:11AM +0200, Ingo Molnar wrote:
>
> * Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote:
>
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -564,7 +564,7 @@ static void kprobe_optimizer(struct work_struct *work)
> > cpus_read_lock();
> > mutex_lock(&text_mutex);
> > /* Lock modules while optimizing kprobes */
> > - mutex_lock(&module_mutex);
> > + lock_modules();
> >
> > /*
> > * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
> > @@ -589,7 +589,7 @@ static void kprobe_optimizer(struct work_struct *work)
> > /* Step 4: Free cleaned kprobes after quiesence period */
> > do_free_cleaned_kprobes();
> >
> > - mutex_unlock(&module_mutex);
> > + unlock_modules();
> > mutex_unlock(&text_mutex);
> > cpus_read_unlock();
>
> BTW., it would be nice to expand on the comments above - exactly which
> parts of the modules code is being serialized against and why?
>
> We already hold the text_mutex here, which should protect against most
> kprobes related activities interfering - and it's unclear (to me)
> which part of the modules code is being serialized with here, and the
> 'lock modules while optimizing kprobes' comments is unhelpful. :-)
>
> Thanks,
>
> Ingo

AFAIK, only if you need to call find_module(), you ever need to acquire
this mutex. 99% of time it is internally taken care by kernel/module.c.

I cannot make up any obvious reason to acquire it here.

/Jarkko

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