[v5,1/6] kprobes: Remove dependency to the module_mutex

Commit Message

Jarkko Sakkinen July 24, 2020, 5:05 a.m. UTC

Add lock_modules() and unlock_modules() wrappers for acquiring module_mutex
in order to remove the compile time dependency to it.

Cc: [e-mail]
Cc: Andi Kleen <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Suggested-by: Masami Hiramatsu <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>
---
 include/linux/module.h      | 18 ++++++++++++++++++
 kernel/kprobes.c            |  4 ++--
 kernel/trace/trace_kprobe.c |  4 ++--
 3 files changed, 22 insertions(+), 4 deletions(-)

Comments

Ingo Molnar July 24, 2020, 9:13 a.m. UTC | #1

* Jarkko Sakkinen <[e-mail]> wrote:

> Add lock_modules() and unlock_modules() wrappers for acquiring module_mutex
> in order to remove the compile time dependency to it.
> 
> Cc: [e-mail]
> Cc: Andi Kleen <[e-mail]>
> Cc: Peter Zijlstra <[e-mail]>
> Suggested-by: Masami Hiramatsu <[e-mail]>
> Signed-off-by: Jarkko Sakkinen <[e-mail]>
> ---
>  include/linux/module.h      | 18 ++++++++++++++++++
>  kernel/kprobes.c            |  4 ++--
>  kernel/trace/trace_kprobe.c |  4 ++--
>  3 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 2e6670860d27..8850b9692b8f 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -705,6 +705,16 @@ static inline bool is_livepatch_module(struct module *mod)
>  bool is_module_sig_enforced(void);
>  void set_module_sig_enforced(void);
>  
> +static inline void lock_modules(void)
> +{
> +	mutex_lock(&module_mutex);
> +}
> +
> +static inline void unlock_modules(void)
> +{
> +	mutex_unlock(&module_mutex);
> +}
> +
>  #else /* !CONFIG_MODULES... */
>  
>  static inline struct module *__module_address(unsigned long addr)
> @@ -852,6 +862,14 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr)
>  	return ptr;
>  }
>  
> +static inline void lock_modules(void)
> +{
> +}
> +
> +static inline void unlock_modules(void)
> +{
> +}

Minor namespace nit: when introducing new locking wrappers please 
standardize on the XYZ_lock()/XYZ_unlock() nomenclature, i.e.:

	modules_lock()
	...
	modules_unlock()

Similarly to the mutex_lock/unlock(&module_mutex) API that it is 
wrapping.

Also, JFYI, the overwhelming majority of the modules related APIs use 
module_*(), i.e. singular - not plural, so 
module_lock()/module_unlock() would be the more canonical choice. 
(But both sound fine to me)

Thanks,

	Ingo

Ingo Molnar July 24, 2020, 9:17 a.m. UTC | #2

* Jarkko Sakkinen <[e-mail]> 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

Mike Rapoport July 24, 2020, 10:22 a.m. UTC | #3

On Fri, Jul 24, 2020 at 08:05:48AM +0300, Jarkko Sakkinen wrote:
> Add lock_modules() and unlock_modules() wrappers for acquiring module_mutex
> in order to remove the compile time dependency to it.
> 
> Cc: [e-mail]
> Cc: Andi Kleen <[e-mail]>
> Cc: Peter Zijlstra <[e-mail]>
> Suggested-by: Masami Hiramatsu <[e-mail]>
> Signed-off-by: Jarkko Sakkinen <[e-mail]>
> ---
>  include/linux/module.h      | 18 ++++++++++++++++++
>  kernel/kprobes.c            |  4 ++--
>  kernel/trace/trace_kprobe.c |  4 ++--
>  3 files changed, 22 insertions(+), 4 deletions(-)

Any reason to convert only kprobes to the new API and leave others with
opencoded implementation?
 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 2e6670860d27..8850b9692b8f 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -705,6 +705,16 @@ static inline bool is_livepatch_module(struct module *mod)
>  bool is_module_sig_enforced(void);
>  void set_module_sig_enforced(void);
>  
> +static inline void lock_modules(void)
> +{
> +	mutex_lock(&module_mutex);
> +}
> +
> +static inline void unlock_modules(void)
> +{
> +	mutex_unlock(&module_mutex);
> +}
> +
>  #else /* !CONFIG_MODULES... */
>  
>  static inline struct module *__module_address(unsigned long addr)
> @@ -852,6 +862,14 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr)
>  	return ptr;
>  }
>  
> +static inline void lock_modules(void)
> +{
> +}
> +
> +static inline void unlock_modules(void)
> +{
> +}
> +
>  #endif /* CONFIG_MODULES */
>  
>  #ifdef CONFIG_SYSFS
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 2e97febeef77..4e46d96d4e16 100644
> --- 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();
>  
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index aefb6065b508..710ec6a6aa8f 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -122,9 +122,9 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
>  	if (!p)
>  		return true;
>  	*p = '\0';
> -	mutex_lock(&module_mutex);
> +	lock_modules();
>  	ret = !!find_module(tk->symbol);
> -	mutex_unlock(&module_mutex);
> +	unlock_modules();
>  	*p = ':';
>  
>  	return ret;
> -- 
> 2.25.1
>

Masami Hiramatsu (Google) July 24, 2020, 2:46 p.m. UTC | #4

On Fri, 24 Jul 2020 08:05:48 +0300
Jarkko Sakkinen <[e-mail]> wrote:

> Add lock_modules() and unlock_modules() wrappers for acquiring module_mutex
> in order to remove the compile time dependency to it.

This subject is a bit confusing. This is just wrapping modules_mutex in
kpprobes. We still have compile time dependency, e.g. module_state, right?

Thank you,

> 
> Cc: [e-mail]
> Cc: Andi Kleen <[e-mail]>
> Cc: Peter Zijlstra <[e-mail]>
> Suggested-by: Masami Hiramatsu <[e-mail]>
> Signed-off-by: Jarkko Sakkinen <[e-mail]>
> ---
>  include/linux/module.h      | 18 ++++++++++++++++++
>  kernel/kprobes.c            |  4 ++--
>  kernel/trace/trace_kprobe.c |  4 ++--
>  3 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 2e6670860d27..8850b9692b8f 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -705,6 +705,16 @@ static inline bool is_livepatch_module(struct module *mod)
>  bool is_module_sig_enforced(void);
>  void set_module_sig_enforced(void);
>  
> +static inline void lock_modules(void)
> +{
> +	mutex_lock(&module_mutex);
> +}
> +
> +static inline void unlock_modules(void)
> +{
> +	mutex_unlock(&module_mutex);
> +}
> +
>  #else /* !CONFIG_MODULES... */
>  
>  static inline struct module *__module_address(unsigned long addr)
> @@ -852,6 +862,14 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr)
>  	return ptr;
>  }
>  
> +static inline void lock_modules(void)
> +{
> +}
> +
> +static inline void unlock_modules(void)
> +{
> +}
> +
>  #endif /* CONFIG_MODULES */
>  
>  #ifdef CONFIG_SYSFS
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 2e97febeef77..4e46d96d4e16 100644
> --- 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();
>  
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index aefb6065b508..710ec6a6aa8f 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -122,9 +122,9 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
>  	if (!p)
>  		return true;
>  	*p = '\0';
> -	mutex_lock(&module_mutex);
> +	lock_modules();
>  	ret = !!find_module(tk->symbol);
> -	mutex_unlock(&module_mutex);
> +	unlock_modules();
>  	*p = ':';
>  
>  	return ret;
> -- 
> 2.25.1
>

Jarkko Sakkinen July 25, 2020, 2:36 a.m. UTC | #5

On Fri, Jul 24, 2020 at 11:13:19AM +0200, Ingo Molnar wrote:
> 
> * Jarkko Sakkinen <[e-mail]> wrote:
> 
> > Add lock_modules() and unlock_modules() wrappers for acquiring module_mutex
> > in order to remove the compile time dependency to it.
> > 
> > Cc: [e-mail]
> > Cc: Andi Kleen <[e-mail]>
> > Cc: Peter Zijlstra <[e-mail]>
> > Suggested-by: Masami Hiramatsu <[e-mail]>
> > Signed-off-by: Jarkko Sakkinen <[e-mail]>
> > ---
> >  include/linux/module.h      | 18 ++++++++++++++++++
> >  kernel/kprobes.c            |  4 ++--
> >  kernel/trace/trace_kprobe.c |  4 ++--
> >  3 files changed, 22 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/module.h b/include/linux/module.h
> > index 2e6670860d27..8850b9692b8f 100644
> > --- a/include/linux/module.h
> > +++ b/include/linux/module.h
> > @@ -705,6 +705,16 @@ static inline bool is_livepatch_module(struct module *mod)
> >  bool is_module_sig_enforced(void);
> >  void set_module_sig_enforced(void);
> >  
> > +static inline void lock_modules(void)
> > +{
> > +	mutex_lock(&module_mutex);
> > +}
> > +
> > +static inline void unlock_modules(void)
> > +{
> > +	mutex_unlock(&module_mutex);
> > +}
> > +
> >  #else /* !CONFIG_MODULES... */
> >  
> >  static inline struct module *__module_address(unsigned long addr)
> > @@ -852,6 +862,14 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr)
> >  	return ptr;
> >  }
> >  
> > +static inline void lock_modules(void)
> > +{
> > +}
> > +
> > +static inline void unlock_modules(void)
> > +{
> > +}
> 
> Minor namespace nit: when introducing new locking wrappers please 
> standardize on the XYZ_lock()/XYZ_unlock() nomenclature, i.e.:
> 
> 	modules_lock()
> 	...
> 	modules_unlock()
> 
> Similarly to the mutex_lock/unlock(&module_mutex) API that it is 
> wrapping.
> 
> Also, JFYI, the overwhelming majority of the modules related APIs use 
> module_*(), i.e. singular - not plural, so 
> module_lock()/module_unlock() would be the more canonical choice. 
> (But both sound fine to me)

Thanks, I renamed them as module_lock() and module_unlock().

> Thanks,
> 
> 	Ingo

/Jarkko

Jarkko Sakkinen July 25, 2020, 2:42 a.m. UTC | #6

On Fri, Jul 24, 2020 at 01:22:58PM +0300, Mike Rapoport wrote:
> On Fri, Jul 24, 2020 at 08:05:48AM +0300, Jarkko Sakkinen wrote:
> > Add lock_modules() and unlock_modules() wrappers for acquiring module_mutex
> > in order to remove the compile time dependency to it.
> > 
> > Cc: [e-mail]
> > Cc: Andi Kleen <[e-mail]>
> > Cc: Peter Zijlstra <[e-mail]>
> > Suggested-by: Masami Hiramatsu <[e-mail]>
> > Signed-off-by: Jarkko Sakkinen <[e-mail]>
> > ---
> >  include/linux/module.h      | 18 ++++++++++++++++++
> >  kernel/kprobes.c            |  4 ++--
> >  kernel/trace/trace_kprobe.c |  4 ++--
> >  3 files changed, 22 insertions(+), 4 deletions(-)
> 
> Any reason to convert only kprobes to the new API and leave others with
> opencoded implementation?

Not anything particular.

Lets see:

$ git --no-pager grep "mutex_lock(&module_mutex)"
arch/powerpc/platforms/powernv/pci-cxl.c:       mutex_lock(&module_mutex);
drivers/gpu/drm/drm_fb_helper.c:        mutex_lock(&module_mutex);
include/linux/module.h: mutex_lock(&module_mutex);
kernel/livepatch/core.c:        mutex_lock(&module_mutex);
kernel/livepatch/core.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);
kernel/module.c:        mutex_lock(&module_mutex);

I could refine this commit to patch these sites. Or should I split it
into multiple?

/Jarkko

Jarkko Sakkinen July 25, 2020, 2:48 a.m. UTC | #7

On Fri, Jul 24, 2020 at 11:46:31PM +0900, Masami Hiramatsu wrote:
> On Fri, 24 Jul 2020 08:05:48 +0300
> Jarkko Sakkinen <[e-mail]> wrote:
> 
> > Add lock_modules() and unlock_modules() wrappers for acquiring module_mutex
> > in order to remove the compile time dependency to it.
> 
> This subject is a bit confusing. This is just wrapping modules_mutex in
> kpprobes. We still have compile time dependency, e.g. module_state, right?

Yes. This more like a preliminary change to make that happen. The
actual flagging is in 6/6 ("Remove CONFIG_MODULE dependency").

Maybe a better angle would be to make this update all sites that
deal with module_mutex [*] and base the whole rationale on that?

[*] https://lore.kernel.org/lkml/[e-mail]/

/Jarkko

Jarkko Sakkinen July 25, 2020, 3:01 a.m. UTC | #8

On Fri, Jul 24, 2020 at 11:17:11AM +0200, Ingo Molnar wrote:
> 
> * Jarkko Sakkinen <[e-mail]> 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

Ingo Molnar July 25, 2020, 10:21 a.m. UTC | #9

* Jarkko Sakkinen <[e-mail]> wrote:

> On Fri, Jul 24, 2020 at 11:17:11AM +0200, Ingo Molnar wrote:
> > 
> > * Jarkko Sakkinen <[e-mail]> 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.

If it's unnecessary, then it needs to be removed.

If it's necessary, then it needs to be documented better.

Thanks,

	Ingo

Masami Hiramatsu (Google) July 28, 2020, 7:34 a.m. UTC | #10

On Sat, 25 Jul 2020 12:21:10 +0200
Ingo Molnar <[e-mail]> wrote:

> 
> * Jarkko Sakkinen <[e-mail]> wrote:
> 
> > On Fri, Jul 24, 2020 at 11:17:11AM +0200, Ingo Molnar wrote:
> > > 
> > > * Jarkko Sakkinen <[e-mail]> 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.
> 
> If it's unnecessary, then it needs to be removed.
> 
> If it's necessary, then it needs to be documented better.

Good catch! This is not needed anymore.
It has been introduced to avoid conflict with text modification, at that
point we didn't get text_mutex. But after commit f1c6ece23729 ("kprobes: Fix 
potential deadlock in kprobe_optimizer()") moved the text_mutex in the current
position, we don't need it. (and anyway, keeping kprobe_mutex locked means
any module unloading will be stopped inside kprobes_module_callback())

This may help?

From 2355ecd941c3234b12a6de7443592848ed4e2087 Mon Sep 17 00:00:00 2001
From: Masami Hiramatsu <[e-mail]>
Date: Tue, 28 Jul 2020 16:32:34 +0900
Subject: [PATCH] kprobes: Remove unneeded module_mutex lock from the optimizer

Remove unneeded module_mutex locking from the optimizer. Since
we already locks both kprobe_mutex and text_mutex in the optimizer,
text will not be changed and the module unloading will be stopped
inside kprobes_module_callback().

Suggested-by: Ingo Molnar <[e-mail]>
Signed-off-by: Masami Hiramatsu <[e-mail]>
---
 kernel/kprobes.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 4a904cc56d68..d1b02e890793 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -563,8 +563,6 @@ static void kprobe_optimizer(struct work_struct *work)
 	mutex_lock(&kprobe_mutex);
 	cpus_read_lock();
 	mutex_lock(&text_mutex);
-	/* Lock modules while optimizing kprobes */
-	mutex_lock(&module_mutex);
 
 	/*
 	 * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
@@ -589,7 +587,6 @@ static void kprobe_optimizer(struct work_struct *work)
 	/* Step 4: Free cleaned kprobes after quiesence period */
 	do_free_cleaned_kprobes();
 
-	mutex_unlock(&module_mutex);
 	mutex_unlock(&text_mutex);
 	cpus_read_unlock();

Jarkko Sakkinen Aug. 17, 2020, 9:22 p.m. UTC | #11

On Tue, Jul 28, 2020 at 04:34:00PM +0900, Masami Hiramatsu wrote:
> On Sat, 25 Jul 2020 12:21:10 +0200
> Ingo Molnar <[e-mail]> wrote:
> 
> > 
> > * Jarkko Sakkinen <[e-mail]> wrote:
> > 
> > > On Fri, Jul 24, 2020 at 11:17:11AM +0200, Ingo Molnar wrote:
> > > > 
> > > > * Jarkko Sakkinen <[e-mail]> 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.
> > 
> > If it's unnecessary, then it needs to be removed.
> > 
> > If it's necessary, then it needs to be documented better.
> 
> Good catch! This is not needed anymore.
> It has been introduced to avoid conflict with text modification, at that
> point we didn't get text_mutex. But after commit f1c6ece23729 ("kprobes: Fix 
> potential deadlock in kprobe_optimizer()") moved the text_mutex in the current
> position, we don't need it. (and anyway, keeping kprobe_mutex locked means
> any module unloading will be stopped inside kprobes_module_callback())
> 
> This may help?

Hey, thanks a lot. This will help to clean my patch set. I'll send a
follow up version as soon I'm on track with my work.  I have to recall
my set of changes and backtrack some of the discussion.

I was two weeks in vacation and last week had bunch of network
connectivity issues last week. Anyway, enough time for details to fade
away :-)

/Jarkko

> 
> From 2355ecd941c3234b12a6de7443592848ed4e2087 Mon Sep 17 00:00:00 2001
> From: Masami Hiramatsu <[e-mail]>
> Date: Tue, 28 Jul 2020 16:32:34 +0900
> Subject: [PATCH] kprobes: Remove unneeded module_mutex lock from the optimizer
> 
> Remove unneeded module_mutex locking from the optimizer. Since
> we already locks both kprobe_mutex and text_mutex in the optimizer,
> text will not be changed and the module unloading will be stopped
> inside kprobes_module_callback().
> 
> Suggested-by: Ingo Molnar <[e-mail]>
> Signed-off-by: Masami Hiramatsu <[e-mail]>
> ---
>  kernel/kprobes.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 4a904cc56d68..d1b02e890793 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -563,8 +563,6 @@ static void kprobe_optimizer(struct work_struct *work)
>  	mutex_lock(&kprobe_mutex);
>  	cpus_read_lock();
>  	mutex_lock(&text_mutex);
> -	/* Lock modules while optimizing kprobes */
> -	mutex_lock(&module_mutex);
>  
>  	/*
>  	 * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
> @@ -589,7 +587,6 @@ static void kprobe_optimizer(struct work_struct *work)
>  	/* Step 4: Free cleaned kprobes after quiesence period */
>  	do_free_cleaned_kprobes();
>  
> -	mutex_unlock(&module_mutex);
>  	mutex_unlock(&text_mutex);
>  	cpus_read_unlock();
>  
> -- 
> 2.25.1
> -- 
> Masami Hiramatsu <[e-mail]>

Patch

diff --git a/include/linux/module.h b/include/linux/module.h
index 2e6670860d27..8850b9692b8f 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -705,6 +705,16 @@  static inline bool is_livepatch_module(struct module *mod)
 bool is_module_sig_enforced(void);
 void set_module_sig_enforced(void);
 
+static inline void lock_modules(void)
+{
+	mutex_lock(&module_mutex);
+}
+
+static inline void unlock_modules(void)
+{
+	mutex_unlock(&module_mutex);
+}
+
 #else /* !CONFIG_MODULES... */
 
 static inline struct module *__module_address(unsigned long addr)
@@ -852,6 +862,14 @@  void *dereference_module_function_descriptor(struct module *mod, void *ptr)
 	return ptr;
 }
 
+static inline void lock_modules(void)
+{
+}
+
+static inline void unlock_modules(void)
+{
+}
+
 #endif /* CONFIG_MODULES */
 
 #ifdef CONFIG_SYSFS
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 2e97febeef77..4e46d96d4e16 100644
--- 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();
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index aefb6065b508..710ec6a6aa8f 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -122,9 +122,9 @@  static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
 	if (!p)
 		return true;
 	*p = '\0';
-	mutex_lock(&module_mutex);
+	lock_modules();
 	ret = !!find_module(tk->symbol);
-	mutex_unlock(&module_mutex);
+	unlock_modules();
 	*p = ':';
 
 	return ret;