[PATCH] preempt: add in_serving_irq() and apply to rcutiny and vsprintf

[PATCH] preempt: add in_serving_irq() and apply to rcutiny and vsprintf

[Changbin Du]

At some places we need to determine whether we're in nmi, hardirq or
softirq context. This adds a macro in_serving_irq() as a shortcut for
that.

Meanwhile, apply this new macro to existing code in rcutiny and vsprintf.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
---
 include/linux/preempt.h | 4 +++-
 include/linux/rcutiny.h | 3 +--
 lib/vsprintf.c          | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 9881eac0698f..9a1c924e2c6c 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -92,12 +92,14 @@
  * in_nmi()		- We're in NMI context
  * in_hardirq()		- We're in hard IRQ context
  * in_serving_softirq()	- We're in softirq context
+ * in_serving_irq()	- We're in nmi, hardirq or softirq context
  * in_task()		- We're in task context
  */
 #define in_nmi()		(nmi_count())
 #define in_hardirq()		(hardirq_count())
 #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
-#define in_task()		(!(in_nmi() | in_hardirq() | in_serving_softirq()))
+#define in_serving_irq()	(in_nmi() | in_hardirq() | in_serving_softirq())
+#define in_task()		(!in_serving_irq())
 
 /*
  * The following macros are deprecated and should not be used in new code:
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 7fedbd33d5d2..812d42f22e9c 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -87,8 +87,7 @@ static inline void rcu_irq_exit_irqson(void) { }
 static inline void rcu_irq_enter_irqson(void) { }
 static inline void rcu_irq_exit(void) { }
 static inline void rcu_irq_exit_check_preempt(void) { }
-#define rcu_is_idle_cpu(cpu) \
-	(is_idle_task(current) && !in_nmi() && !in_hardirq() && !in_serving_softirq())
+#define rcu_is_idle_cpu(cpu) (is_idle_task(current) && !in_serving_irq())
 static inline void exit_rcu(void) { }
 static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 {
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 2c5b4351330c..9324439c8543 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -865,7 +865,7 @@ char *restricted_pointer(char *buf, char *end, const void *ptr,
 		 * kptr_restrict==1 cannot be used in IRQ context
 		 * because its test for CAP_SYSLOG would be meaningless.
 		 */
-		if (in_hardirq() || in_serving_softirq() || in_nmi()) {
+		if (in_serving_irq()) {
 			if (spec.field_width == -1)
 				spec.field_width = 2 * sizeof(ptr);
 			return error_string(buf, end, "pK-error", spec);
-- 
2.30.2

Re: [PATCH] preempt: add in_serving_irq() and apply to rcutiny and vsprintf

[Boqun Feng]

On Sat, Aug 14, 2021 at 09:42:34AM +0800, Changbin Du wrote:
> At some places we need to determine whether we're in nmi, hardirq or
> softirq context. This adds a macro in_serving_irq() as a shortcut for
> that.
> 
> Meanwhile, apply this new macro to existing code in rcutiny and vsprintf.
> 
> Signed-off-by: Changbin Du <changbin.du@gmail.com>
> ---
>  include/linux/preempt.h | 4 +++-
>  include/linux/rcutiny.h | 3 +--
>  lib/vsprintf.c          | 2 +-
>  3 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 9881eac0698f..9a1c924e2c6c 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -92,12 +92,14 @@
>   * in_nmi()		- We're in NMI context
>   * in_hardirq()		- We're in hard IRQ context
>   * in_serving_softirq()	- We're in softirq context
> + * in_serving_irq()	- We're in nmi, hardirq or softirq context
>   * in_task()		- We're in task context
>   */
>  #define in_nmi()		(nmi_count())
>  #define in_hardirq()		(hardirq_count())
>  #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
> -#define in_task()		(!(in_nmi() | in_hardirq() | in_serving_softirq()))
> +#define in_serving_irq()	(in_nmi() | in_hardirq() | in_serving_softirq())
> +#define in_task()		(!in_serving_irq())
>  

So in_serving_irq() is !in_task(), right? If so, why not...

>  /*
>   * The following macros are deprecated and should not be used in new code:
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 7fedbd33d5d2..812d42f22e9c 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -87,8 +87,7 @@ static inline void rcu_irq_exit_irqson(void) { }
>  static inline void rcu_irq_enter_irqson(void) { }
>  static inline void rcu_irq_exit(void) { }
>  static inline void rcu_irq_exit_check_preempt(void) { }
> -#define rcu_is_idle_cpu(cpu) \
> -	(is_idle_task(current) && !in_nmi() && !in_hardirq() && !in_serving_softirq())
> +#define rcu_is_idle_cpu(cpu) (is_idle_task(current) && !in_serving_irq())

... use in_task() here, and ...

>  static inline void exit_rcu(void) { }
>  static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t)
>  {
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 2c5b4351330c..9324439c8543 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -865,7 +865,7 @@ char *restricted_pointer(char *buf, char *end, const void *ptr,
>  		 * kptr_restrict==1 cannot be used in IRQ context
>  		 * because its test for CAP_SYSLOG would be meaningless.
>  		 */
> -		if (in_hardirq() || in_serving_softirq() || in_nmi()) {
> +		if (in_serving_irq()) {

... use !in_task() here?

And don't introduce the in_serving_irq() at all.

Regards,
Boqun

>  			if (spec.field_width == -1)
>  				spec.field_width = 2 * sizeof(ptr);
>  			return error_string(buf, end, "pK-error", spec);
> -- 
> 2.30.2
> 

Re: [PATCH] preempt: add in_serving_irq() and apply to rcutiny and vsprintf

[Changbin Du]

On Tue, Aug 17, 2021 at 12:03:16AM +0800, Boqun Feng wrote:
> On Sat, Aug 14, 2021 at 09:42:34AM +0800, Changbin Du wrote:
> > At some places we need to determine whether we're in nmi, hardirq or
> > softirq context. This adds a macro in_serving_irq() as a shortcut for
> > that.
> > 
> > Meanwhile, apply this new macro to existing code in rcutiny and vsprintf.
> > 
> > Signed-off-by: Changbin Du <changbin.du@gmail.com>
> > ---
> >  include/linux/preempt.h | 4 +++-
> >  include/linux/rcutiny.h | 3 +--
> >  lib/vsprintf.c          | 2 +-
> >  3 files changed, 5 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> > index 9881eac0698f..9a1c924e2c6c 100644
> > --- a/include/linux/preempt.h
> > +++ b/include/linux/preempt.h
> > @@ -92,12 +92,14 @@
> >   * in_nmi()		- We're in NMI context
> >   * in_hardirq()		- We're in hard IRQ context
> >   * in_serving_softirq()	- We're in softirq context
> > + * in_serving_irq()	- We're in nmi, hardirq or softirq context
> >   * in_task()		- We're in task context
> >   */
> >  #define in_nmi()		(nmi_count())
> >  #define in_hardirq()		(hardirq_count())
> >  #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
> > -#define in_task()		(!(in_nmi() | in_hardirq() | in_serving_softirq()))
> > +#define in_serving_irq()	(in_nmi() | in_hardirq() | in_serving_softirq())
> > +#define in_task()		(!in_serving_irq())
> >  
> 
> So in_serving_irq() is !in_task(), right? If so, why not...
> 
Adding in_serving_irq() is to reflect the real purpose so improve readability.
And can we preserve that !in_task() means in serving irq context in future? I don't know.

-- 
Cheers,
Changbin Du

Re: [PATCH] preempt: add in_serving_irq() and apply to rcutiny and vsprintf

[Boqun Feng]

[Cc Thomas and Frederic since they contributed the clean-up to these
macros recently]

Background for discussion:

	https://lore.kernel.org/lkml/20210814014234.51395-1-changbin.du@gmail.com/

On Thu, Aug 19, 2021 at 07:59:16AM +0800, Changbin Du wrote:
> On Tue, Aug 17, 2021 at 12:03:16AM +0800, Boqun Feng wrote:
> > On Sat, Aug 14, 2021 at 09:42:34AM +0800, Changbin Du wrote:
> > > At some places we need to determine whether we're in nmi, hardirq or
> > > softirq context. This adds a macro in_serving_irq() as a shortcut for
> > > that.
> > > 
> > > Meanwhile, apply this new macro to existing code in rcutiny and vsprintf.
> > > 
> > > Signed-off-by: Changbin Du <changbin.du@gmail.com>
> > > ---
> > >  include/linux/preempt.h | 4 +++-
> > >  include/linux/rcutiny.h | 3 +--
> > >  lib/vsprintf.c          | 2 +-
> > >  3 files changed, 5 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> > > index 9881eac0698f..9a1c924e2c6c 100644
> > > --- a/include/linux/preempt.h
> > > +++ b/include/linux/preempt.h
> > > @@ -92,12 +92,14 @@
> > >   * in_nmi()		- We're in NMI context
> > >   * in_hardirq()		- We're in hard IRQ context
> > >   * in_serving_softirq()	- We're in softirq context
> > > + * in_serving_irq()	- We're in nmi, hardirq or softirq context
> > >   * in_task()		- We're in task context
> > >   */
> > >  #define in_nmi()		(nmi_count())
> > >  #define in_hardirq()		(hardirq_count())
> > >  #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
> > > -#define in_task()		(!(in_nmi() | in_hardirq() | in_serving_softirq()))
> > > +#define in_serving_irq()	(in_nmi() | in_hardirq() | in_serving_softirq())
> > > +#define in_task()		(!in_serving_irq())
> > >  
> > 
> > So in_serving_irq() is !in_task(), right? If so, why not...
> > 
> Adding in_serving_irq() is to reflect the real purpose so improve readability.
> And can we preserve that !in_task() means in serving irq context in future? I don't know.
> 

Sure, no one could predict the future. But if a third context (other
than thread context and {hard,soft}irq context) comes up, which I think
is highly unlikely, we could (and should) audit all callsites of
in_task() for necessary adjustment. And introducing in_serving_irq()
won't help us in that case, because we will still need to audit usage of
in_serving_irq(), for example, let's say rcu_is_idle_cpu() for RCU_TINY
is defined as

	#define rcu_is_idle_cpu(cpu) (is_idle_task(current) && !in_serving_irq())

and we have a new type of context, and we can use in_other() to test
whether we are in it. Now even with in_serving_irq() introduced, we
still need to make sure the correct version of rcu_is_idle_cpu() is
either

	(is_idle_task(current) && (!in_serving_irq() && !in_other()))

or
	
	(is_idle_task(current) && !in_serving_irq())

Therefore, I don't see the point of introducing in_serving_irq().

Regards,
Boqun

> -- 
> Cheers,
> Changbin Du

Re: [PATCH] preempt: add in_serving_irq() and apply to rcutiny and vsprintf

[Changbin Du]

On Thu, Aug 19, 2021 at 09:56:45AM +0800, Boqun Feng wrote:
> [Cc Thomas and Frederic since they contributed the clean-up to these
> macros recently]
> 
> Background for discussion:
> 
> 	https://lore.kernel.org/lkml/20210814014234.51395-1-changbin.du@gmail.com/
> 
> On Thu, Aug 19, 2021 at 07:59:16AM +0800, Changbin Du wrote:
> > On Tue, Aug 17, 2021 at 12:03:16AM +0800, Boqun Feng wrote:
> > > On Sat, Aug 14, 2021 at 09:42:34AM +0800, Changbin Du wrote:
> > > > At some places we need to determine whether we're in nmi, hardirq or
> > > > softirq context. This adds a macro in_serving_irq() as a shortcut for
> > > > that.
> > > > 
> > > > Meanwhile, apply this new macro to existing code in rcutiny and vsprintf.
> > > > 
> > > > Signed-off-by: Changbin Du <changbin.du@gmail.com>
> > > > ---
> > > >  include/linux/preempt.h | 4 +++-
> > > >  include/linux/rcutiny.h | 3 +--
> > > >  lib/vsprintf.c          | 2 +-
> > > >  3 files changed, 5 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> > > > index 9881eac0698f..9a1c924e2c6c 100644
> > > > --- a/include/linux/preempt.h
> > > > +++ b/include/linux/preempt.h
> > > > @@ -92,12 +92,14 @@
> > > >   * in_nmi()		- We're in NMI context
> > > >   * in_hardirq()		- We're in hard IRQ context
> > > >   * in_serving_softirq()	- We're in softirq context
> > > > + * in_serving_irq()	- We're in nmi, hardirq or softirq context
> > > >   * in_task()		- We're in task context
> > > >   */
> > > >  #define in_nmi()		(nmi_count())
> > > >  #define in_hardirq()		(hardirq_count())
> > > >  #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
> > > > -#define in_task()		(!(in_nmi() | in_hardirq() | in_serving_softirq()))
> > > > +#define in_serving_irq()	(in_nmi() | in_hardirq() | in_serving_softirq())
> > > > +#define in_task()		(!in_serving_irq())
> > > >  
> > > 
> > > So in_serving_irq() is !in_task(), right? If so, why not...
> > > 
> > Adding in_serving_irq() is to reflect the real purpose so improve readability.
> > And can we preserve that !in_task() means in serving irq context in future? I don't know.
> > 
> 
> Sure, no one could predict the future. But if a third context (other
> than thread context and {hard,soft}irq context) comes up, which I think
> is highly unlikely, we could (and should) audit all callsites of
> in_task() for necessary adjustment. And introducing in_serving_irq()
> won't help us in that case, because we will still need to audit usage of
> in_serving_irq(), for example, let's say rcu_is_idle_cpu() for RCU_TINY
> is defined as
> 
> 	#define rcu_is_idle_cpu(cpu) (is_idle_task(current) && !in_serving_irq())
> 
> and we have a new type of context, and we can use in_other() to test
> whether we are in it. Now even with in_serving_irq() introduced, we
> still need to make sure the correct version of rcu_is_idle_cpu() is
> either
> 
> 	(is_idle_task(current) && (!in_serving_irq() && !in_other()))
> 
> or
> 	
> 	(is_idle_task(current) && !in_serving_irq())
> 
> Therefore, I don't see the point of introducing in_serving_irq().
>
ok, as in_serving_irq() is only used in two places, it is not common to judge if
it is in serving irq context. So this new macro doesn't help much.

> Regards,
> Boqun
> 
> > -- 
> > Cheers,
> > Changbin Du

-- 
Cheers,
Changbin Du