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[PATCH v4 2/6] srcu: Add srcu_read_lock_fast_notrace() and srcu_read_unlock_fast_notrace()

Paul E. McKenney posted 6 patches 6 months, 3 weeks ago
There is a newer version of this series
[PATCH v4 2/6] srcu: Add srcu_read_lock_fast_notrace() and srcu_read_unlock_fast_notrace()
Posted by Paul E. McKenney 6 months, 3 weeks ago 
This commit adds no-trace variants of the srcu_read_lock_fast() and
srcu_read_unlock_fast() functions for tracing use.

[ paulmck: Apply notrace feedback from Joel Fernandes, Steven Rostedt, and Mathieu Desnoyers. ]

Link: https://lore.kernel.org/all/20250721162433.10454-1-paulmck@kernel.org
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: <bpf@vger.kernel.org>
---
 include/linux/srcu.h     | 30 ++++++++++++++++++++++++++++--
 include/linux/srcutree.h |  5 +++--
 2 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 478c73d067f7d..ec3b8e27d6c5a 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -271,7 +271,7 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
  * where RCU is watching, that is, from contexts where it would be legal
  * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
  */
-static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires(ssp)
+static inline struct srcu_ctr __percpu notrace *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires(ssp)
 {
 	struct srcu_ctr __percpu *retval;
 
@@ -282,6 +282,20 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *
 	return retval;
 }
 
+/*
+ * Used by tracing, cannot be traced and cannot call lockdep.
+ * See srcu_read_lock_fast() for more information.
+ */
+static inline struct srcu_ctr __percpu *srcu_read_lock_fast_notrace(struct srcu_struct *ssp)
+	__acquires(ssp)
+{
+	struct srcu_ctr __percpu *retval;
+
+	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
+	retval = __srcu_read_lock_fast(ssp);
+	return retval;
+}
+
 /**
  * srcu_down_read_fast - register a new reader for an SRCU-protected structure.
  * @ssp: srcu_struct in which to register the new reader.
@@ -385,7 +399,8 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
  *
  * Exit a light-weight SRCU read-side critical section.
  */
-static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
+static inline void notrace
+srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
 	__releases(ssp)
 {
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
@@ -394,6 +409,17 @@ static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ct
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
 }
 
+/*
+ * Used by tracing, cannot be traced and cannot call lockdep.
+ * See srcu_read_unlock_fast() for more information.
+ */
+static inline void srcu_read_unlock_fast_notrace(struct srcu_struct *ssp,
+						 struct srcu_ctr __percpu *scp) __releases(ssp)
+{
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
+	__srcu_read_unlock_fast(ssp, scp);
+}
+
 /**
  * srcu_up_read_fast - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 043b5a67ef71e..4d2fee4d38289 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -240,7 +240,7 @@ static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ss
  * on architectures that support NMIs but do not supply NMI-safe
  * implementations of this_cpu_inc().
  */
-static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct *ssp)
+static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct srcu_struct *ssp)
 {
 	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
 
@@ -267,7 +267,8 @@ static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct
  * on architectures that support NMIs but do not supply NMI-safe
  * implementations of this_cpu_inc().
  */
-static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
+static inline void notrace
+__srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
 {
 	barrier();  /* Avoid leaking the critical section. */
 	if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))
-- 
2.40.1
Re: [PATCH v4 2/6] srcu: Add srcu_read_lock_fast_notrace() and srcu_read_unlock_fast_notrace()
Posted by Boqun Feng 6 months, 3 weeks ago 
On Wed, Jul 23, 2025 at 01:27:56PM -0700, Paul E. McKenney wrote:
> This commit adds no-trace variants of the srcu_read_lock_fast() and
> srcu_read_unlock_fast() functions for tracing use.
> 
> [ paulmck: Apply notrace feedback from Joel Fernandes, Steven Rostedt, and Mathieu Desnoyers. ]
> 
> Link: https://lore.kernel.org/all/20250721162433.10454-1-paulmck@kernel.org
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: <bpf@vger.kernel.org>
> ---
>  include/linux/srcu.h     | 30 ++++++++++++++++++++++++++++--
>  include/linux/srcutree.h |  5 +++--
>  2 files changed, 31 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index 478c73d067f7d..ec3b8e27d6c5a 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -271,7 +271,7 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
>   * where RCU is watching, that is, from contexts where it would be legal
>   * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
>   */
> -static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires(ssp)
> +static inline struct srcu_ctr __percpu notrace *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires(ssp)

Hmm.. am I missing something, why do we need ot make
srcu_read_lock_fast() notrace? I thought we only need those _notrace()
variants notrace?

Regards,
Boqun

>  {
>  	struct srcu_ctr __percpu *retval;
>  
> @@ -282,6 +282,20 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *
>  	return retval;
>  }
>  
> +/*
> + * Used by tracing, cannot be traced and cannot call lockdep.
> + * See srcu_read_lock_fast() for more information.
> + */
> +static inline struct srcu_ctr __percpu *srcu_read_lock_fast_notrace(struct srcu_struct *ssp)
> +	__acquires(ssp)
> +{
> +	struct srcu_ctr __percpu *retval;
> +
> +	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
> +	retval = __srcu_read_lock_fast(ssp);
> +	return retval;
> +}
> +
>  /**
>   * srcu_down_read_fast - register a new reader for an SRCU-protected structure.
>   * @ssp: srcu_struct in which to register the new reader.
> @@ -385,7 +399,8 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
>   *
>   * Exit a light-weight SRCU read-side critical section.
>   */
> -static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
> +static inline void notrace
> +srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
>  	__releases(ssp)
>  {
>  	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
> @@ -394,6 +409,17 @@ static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ct
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
>  }
>  
> +/*
> + * Used by tracing, cannot be traced and cannot call lockdep.
> + * See srcu_read_unlock_fast() for more information.
> + */
> +static inline void srcu_read_unlock_fast_notrace(struct srcu_struct *ssp,
> +						 struct srcu_ctr __percpu *scp) __releases(ssp)
> +{
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
> +	__srcu_read_unlock_fast(ssp, scp);
> +}
> +
>  /**
>   * srcu_up_read_fast - unregister a old reader from an SRCU-protected structure.
>   * @ssp: srcu_struct in which to unregister the old reader.
> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
> index 043b5a67ef71e..4d2fee4d38289 100644
> --- a/include/linux/srcutree.h
> +++ b/include/linux/srcutree.h
> @@ -240,7 +240,7 @@ static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ss
>   * on architectures that support NMIs but do not supply NMI-safe
>   * implementations of this_cpu_inc().
>   */
> -static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct *ssp)
> +static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct srcu_struct *ssp)
>  {
>  	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
>  
> @@ -267,7 +267,8 @@ static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct
>   * on architectures that support NMIs but do not supply NMI-safe
>   * implementations of this_cpu_inc().
>   */
> -static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
> +static inline void notrace
> +__srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
>  {
>  	barrier();  /* Avoid leaking the critical section. */
>  	if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))
> -- 
> 2.40.1
> 
>
Re: [PATCH v4 2/6] srcu: Add srcu_read_lock_fast_notrace() and srcu_read_unlock_fast_notrace()
Posted by Paul E. McKenney 6 months, 3 weeks ago 
On Wed, Jul 23, 2025 at 01:50:35PM -0700, Boqun Feng wrote:
> On Wed, Jul 23, 2025 at 01:27:56PM -0700, Paul E. McKenney wrote:
> > This commit adds no-trace variants of the srcu_read_lock_fast() and
> > srcu_read_unlock_fast() functions for tracing use.
> > 
> > [ paulmck: Apply notrace feedback from Joel Fernandes, Steven Rostedt, and Mathieu Desnoyers. ]
> > 
> > Link: https://lore.kernel.org/all/20250721162433.10454-1-paulmck@kernel.org
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > Cc: <bpf@vger.kernel.org>
> > ---
> >  include/linux/srcu.h     | 30 ++++++++++++++++++++++++++++--
> >  include/linux/srcutree.h |  5 +++--
> >  2 files changed, 31 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> > index 478c73d067f7d..ec3b8e27d6c5a 100644
> > --- a/include/linux/srcu.h
> > +++ b/include/linux/srcu.h
> > @@ -271,7 +271,7 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
> >   * where RCU is watching, that is, from contexts where it would be legal
> >   * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
> >   */
> > -static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires(ssp)
> > +static inline struct srcu_ctr __percpu notrace *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires(ssp)
> 
> Hmm.. am I missing something, why do we need ot make
> srcu_read_lock_fast() notrace? I thought we only need those _notrace()
> variants notrace?

Good point!  It looks like I got a bit too exuberant here.  I am removing
notrace from srcu_read_lock_fast() and srcu_read_unlock_fast(), but
leaving srcu_read_lock_fast_notrace(), srcu_read_unlock_fast_notrace(),
__srcu_read_lock_fast(), and __srcu_read_unlock_fast() as-is.

							Thanx, Paul

> Regards,
> Boqun
> 
> >  {
> >  	struct srcu_ctr __percpu *retval;
> >  
> > @@ -282,6 +282,20 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *
> >  	return retval;
> >  }
> >  
> > +/*
> > + * Used by tracing, cannot be traced and cannot call lockdep.
> > + * See srcu_read_lock_fast() for more information.
> > + */
> > +static inline struct srcu_ctr __percpu *srcu_read_lock_fast_notrace(struct srcu_struct *ssp)
> > +	__acquires(ssp)
> > +{
> > +	struct srcu_ctr __percpu *retval;
> > +
> > +	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
> > +	retval = __srcu_read_lock_fast(ssp);
> > +	return retval;
> > +}
> > +
> >  /**
> >   * srcu_down_read_fast - register a new reader for an SRCU-protected structure.
> >   * @ssp: srcu_struct in which to register the new reader.
> > @@ -385,7 +399,8 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
> >   *
> >   * Exit a light-weight SRCU read-side critical section.
> >   */
> > -static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
> > +static inline void notrace
> > +srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
> >  	__releases(ssp)
> >  {
> >  	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
> > @@ -394,6 +409,17 @@ static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ct
> >  	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
> >  }
> >  
> > +/*
> > + * Used by tracing, cannot be traced and cannot call lockdep.
> > + * See srcu_read_unlock_fast() for more information.
> > + */
> > +static inline void srcu_read_unlock_fast_notrace(struct srcu_struct *ssp,
> > +						 struct srcu_ctr __percpu *scp) __releases(ssp)
> > +{
> > +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
> > +	__srcu_read_unlock_fast(ssp, scp);
> > +}
> > +
> >  /**
> >   * srcu_up_read_fast - unregister a old reader from an SRCU-protected structure.
> >   * @ssp: srcu_struct in which to unregister the old reader.
> > diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
> > index 043b5a67ef71e..4d2fee4d38289 100644
> > --- a/include/linux/srcutree.h
> > +++ b/include/linux/srcutree.h
> > @@ -240,7 +240,7 @@ static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ss
> >   * on architectures that support NMIs but do not supply NMI-safe
> >   * implementations of this_cpu_inc().
> >   */
> > -static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct *ssp)
> > +static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct srcu_struct *ssp)
> >  {
> >  	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
> >  
> > @@ -267,7 +267,8 @@ static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct
> >   * on architectures that support NMIs but do not supply NMI-safe
> >   * implementations of this_cpu_inc().
> >   */
> > -static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
> > +static inline void notrace
> > +__srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
> >  {
> >  	barrier();  /* Avoid leaking the critical section. */
> >  	if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))
> > -- 
> > 2.40.1
> > 
> >

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