[PATCH 0/5] Remove SRCU-lite in favor of SRCU-fast

[PATCH 0/5] Remove SRCU-lite in favor of SRCU-fast

[Paul E. McKenney]

Hello!

This series removes the deprecated SRCU-lite flavor:

1.	Remove support for SRCU-lite.

2.	Remove SRCU-lite scenarios.

3.	Remove support for SRCU-lite.

4.	Remove SRCU-lite implementation.

5.	Remove SRCU-lite deprecation.

						Thanx, Paul

------------------------------------------------------------------------

 b/include/linux/srcu.h                                     |    2 
 b/include/linux/srcutiny.h                                 |    3 
 b/include/linux/srcutree.h                                 |   38 ----------
 b/kernel/rcu/rcutorture.c                                  |    7 -
 b/kernel/rcu/refscale.c                                    |   32 --------
 b/scripts/checkpatch.pl                                    |    2 
 b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST    |    1 
 include/linux/srcu.h                                       |   47 -------------
 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L      |   10 --
 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot |    3 
 10 files changed, 4 insertions(+), 141 deletions(-)

[PATCH 1/5] torture: Remove support for SRCU-lite

[Paul E. McKenney]

Because SRCU-lite is being replaced by SRCU-fast, this commit removes
support for SRCU-lite from refscale.c.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/refscale.c | 32 +-------------------------------
 1 file changed, 1 insertion(+), 31 deletions(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index f11a7c2af778c..f4b2cea1cce5e 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -246,36 +246,6 @@ static const struct ref_scale_ops srcu_fast_ops = {
 	.name		= "srcu-fast"
 };
 
-static void srcu_lite_ref_scale_read_section(const int nloops)
-{
-	int i;
-	int idx;
-
-	for (i = nloops; i >= 0; i--) {
-		idx = srcu_read_lock_lite(srcu_ctlp);
-		srcu_read_unlock_lite(srcu_ctlp, idx);
-	}
-}
-
-static void srcu_lite_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
-{
-	int i;
-	int idx;
-
-	for (i = nloops; i >= 0; i--) {
-		idx = srcu_read_lock_lite(srcu_ctlp);
-		un_delay(udl, ndl);
-		srcu_read_unlock_lite(srcu_ctlp, idx);
-	}
-}
-
-static const struct ref_scale_ops srcu_lite_ops = {
-	.init		= rcu_sync_scale_init,
-	.readsection	= srcu_lite_ref_scale_read_section,
-	.delaysection	= srcu_lite_ref_scale_delay_section,
-	.name		= "srcu-lite"
-};
-
 #ifdef CONFIG_TASKS_RCU
 
 // Definitions for RCU Tasks ref scale testing: Empty read markers.
@@ -1193,7 +1163,7 @@ ref_scale_init(void)
 	long i;
 	int firsterr = 0;
 	static const struct ref_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &srcu_fast_ops, &srcu_lite_ops, RCU_TRACE_OPS RCU_TASKS_OPS
+		&rcu_ops, &srcu_ops, &srcu_fast_ops, RCU_TRACE_OPS RCU_TASKS_OPS
 		&refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops,
 		&acqrel_ops, &sched_clock_ops, &clock_ops, &jiffies_ops,
 		&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
-- 
2.40.1

Re: [PATCH 1/5] torture: Remove support for SRCU-lite

[Christoph Hellwig]

On Tue, Jun 24, 2025 at 09:13:56AM -0700, Paul E. McKenney wrote:
> Because SRCU-lite is being replaced by SRCU-fast, this commit removes
> support for SRCU-lite from refscale.c.

Please explain how they different and why one is a good enough (or
even better?) replacement for the other.

Re: [PATCH 1/5] torture: Remove support for SRCU-lite

[Paul E. McKenney]

On Wed, Jun 25, 2025 at 05:05:47AM -0700, Christoph Hellwig wrote:
> On Tue, Jun 24, 2025 at 09:13:56AM -0700, Paul E. McKenney wrote:
> > Because SRCU-lite is being replaced by SRCU-fast, this commit removes
> > support for SRCU-lite from refscale.c.
> 
> Please explain how they different and why one is a good enough (or
> even better?) replacement for the other.

Ah, good point, thank you!

How about if I add this to the cover letter?

	Both SRCU-lite and SRCU-fast provide faster readers by dropping
	the smp_mb() call from their lock and unlock primitives.
	The price of this is a pair of added RCU grace periods during
	the SRCU grace period.

	SRCU-fast also adds NMI safety for architectures that have
	NMIs but do not have NMI-safe per-CPU operations.  In addition,
	srcu_read_lock_fast() returns a per-CPU pointer rather than an
	integer, which provides a further speedup compared to SRCU-lite
	by getting rid of array-index calculations.

	There is a trivial mapping from the SRCU-lite API to that
	of SRCU-fast, so we do not expect any transition issues.
	In addition, while SRCU-lite remains in the kernel, checkpatch.pl
	will warn about added SRCU-lite use cases.

	Further read-side speedups are possible, but they amount to only
	about half a nanosecond out of about two nanoseconds (measured on
	my x86 laptop), and they might require some changes to existing
	SRCU code.  These changes are trivial, but we need to see a
	solid need for the additional performance before inconveniencing
	existing users.

							Thanx, Paul

Re: [PATCH 1/5] torture: Remove support for SRCU-lite

[Christoph Hellwig]

On Thu, Jun 26, 2025 at 03:54:06AM -0700, Paul E. McKenney wrote:
> How about if I add this to the cover letter?

Sounds good.  But please also have a very short summary in the
actual commits.  As-is the commit logs completly fail explain to the
why, which is the most important part of a commit log.

Re: [PATCH 1/5] torture: Remove support for SRCU-lite

[Paul E. McKenney]

On Thu, Jun 26, 2025 at 04:03:32AM -0700, Christoph Hellwig wrote:
> On Thu, Jun 26, 2025 at 03:54:06AM -0700, Paul E. McKenney wrote:
> > How about if I add this to the cover letter?
> 
> Sounds good.  But please also have a very short summary in the
> actual commits.  As-is the commit logs completly fail explain to the
> why, which is the most important part of a commit log.

Will do, and again, thank you!

							Thanx, Paul

[PATCH 2/5] rcutorture: Remove SRCU-lite scenarios

[Paul E. McKenney]

This commit prepares for the removal of SRCU-Lite by removing the SRCU-L
rcutorture scenario that tests it.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 tools/testing/selftests/rcutorture/configs/rcu/CFLIST  |  1 -
 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L  | 10 ----------
 .../selftests/rcutorture/configs/rcu/SRCU-L.boot       |  3 ---
 3 files changed, 14 deletions(-)
 delete mode 100644 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
 delete mode 100644 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot

diff --git a/tools/testing/selftests/rcutorture/configs/rcu/CFLIST b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
index 45f572570a8c3..98b6175e5aa09 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
+++ b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
@@ -5,7 +5,6 @@ TREE04
 TREE05
 TREE07
 TREE09
-SRCU-L
 SRCU-N
 SRCU-P
 SRCU-T
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
deleted file mode 100644
index 3b4fa8dbef8a9..0000000000000
--- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
+++ /dev/null
@@ -1,10 +0,0 @@
-CONFIG_RCU_TRACE=n
-CONFIG_SMP=y
-CONFIG_NR_CPUS=6
-CONFIG_HOTPLUG_CPU=y
-CONFIG_PREEMPT_NONE=y
-CONFIG_PREEMPT_VOLUNTARY=n
-CONFIG_PREEMPT=n
-#CHECK#CONFIG_RCU_EXPERT=n
-CONFIG_KPROBES=n
-CONFIG_FTRACE=n
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot
deleted file mode 100644
index 0207b3138c5be..0000000000000
--- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot
+++ /dev/null
@@ -1,3 +0,0 @@
-rcutorture.torture_type=srcu
-rcutorture.reader_flavor=0x4
-rcutorture.fwd_progress=3
-- 
2.40.1

[PATCH 3/5] rcutorture: Remove support for SRCU-lite

[Paul E. McKenney]

Because SRCU-lite is being replaced by SRCU-fast, this commit removes
support for SRCU-lite from rcutorture.c

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/srcu.h    | 2 +-
 kernel/rcu/rcutorture.c | 7 -------
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 900b0d5c05f54..c20dacb563e55 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -49,7 +49,7 @@ int init_srcu_struct(struct srcu_struct *ssp);
 #define SRCU_READ_FLAVOR_LITE	0x4		// srcu_read_lock_lite().
 #define SRCU_READ_FLAVOR_FAST	0x8		// srcu_read_lock_fast().
 #define SRCU_READ_FLAVOR_ALL   (SRCU_READ_FLAVOR_NORMAL | SRCU_READ_FLAVOR_NMI | \
-				SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST) // All of the above.
+				SRCU_READ_FLAVOR_FAST) // All of the above.
 #define SRCU_READ_FLAVOR_SLOWGP	(SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST)
 						// Flavors requiring synchronize_rcu()
 						// instead of smp_mb().
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 213f23f20a64b..7a893d51d02b6 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -718,11 +718,6 @@ static int srcu_torture_read_lock(void)
 		WARN_ON_ONCE(idx & ~0x1);
 		ret += idx << 1;
 	}
-	if (reader_flavor & SRCU_READ_FLAVOR_LITE) {
-		idx = srcu_read_lock_lite(srcu_ctlp);
-		WARN_ON_ONCE(idx & ~0x1);
-		ret += idx << 2;
-	}
 	if (reader_flavor & SRCU_READ_FLAVOR_FAST) {
 		scp = srcu_read_lock_fast(srcu_ctlp);
 		idx = __srcu_ptr_to_ctr(srcu_ctlp, scp);
@@ -756,8 +751,6 @@ static void srcu_torture_read_unlock(int idx)
 	WARN_ON_ONCE((reader_flavor && (idx & ~reader_flavor)) || (!reader_flavor && (idx & ~0x1)));
 	if (reader_flavor & SRCU_READ_FLAVOR_FAST)
 		srcu_read_unlock_fast(srcu_ctlp, __srcu_ctr_to_ptr(srcu_ctlp, (idx & 0x8) >> 3));
-	if (reader_flavor & SRCU_READ_FLAVOR_LITE)
-		srcu_read_unlock_lite(srcu_ctlp, (idx & 0x4) >> 2);
 	if (reader_flavor & SRCU_READ_FLAVOR_NMI)
 		srcu_read_unlock_nmisafe(srcu_ctlp, (idx & 0x2) >> 1);
 	if ((reader_flavor & SRCU_READ_FLAVOR_NORMAL) || !(reader_flavor & SRCU_READ_FLAVOR_ALL))
-- 
2.40.1

[PATCH 4/5] srcu: Remove SRCU-lite implementation

[Paul E. McKenney]

This commit removes the SRCU-lite implementation, which has been replaced
by SRCU-fast.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/srcu.h     | 47 ++--------------------------------------
 include/linux/srcutiny.h |  3 ---
 include/linux/srcutree.h | 38 --------------------------------
 3 files changed, 2 insertions(+), 86 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index c20dacb563e55..cf711a0f440b2 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -46,11 +46,11 @@ int init_srcu_struct(struct srcu_struct *ssp);
 /* Values for SRCU Tree srcu_data ->srcu_reader_flavor, but also used by rcutorture. */
 #define SRCU_READ_FLAVOR_NORMAL	0x1		// srcu_read_lock().
 #define SRCU_READ_FLAVOR_NMI	0x2		// srcu_read_lock_nmisafe().
-#define SRCU_READ_FLAVOR_LITE	0x4		// srcu_read_lock_lite().
+//				0x4		// SRCU-lite is no longer with us.
 #define SRCU_READ_FLAVOR_FAST	0x8		// srcu_read_lock_fast().
 #define SRCU_READ_FLAVOR_ALL   (SRCU_READ_FLAVOR_NORMAL | SRCU_READ_FLAVOR_NMI | \
 				SRCU_READ_FLAVOR_FAST) // All of the above.
-#define SRCU_READ_FLAVOR_SLOWGP	(SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST)
+#define SRCU_READ_FLAVOR_SLOWGP	SRCU_READ_FLAVOR_FAST
 						// Flavors requiring synchronize_rcu()
 						// instead of smp_mb().
 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
@@ -299,33 +299,6 @@ static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *
 	return __srcu_read_lock_fast(ssp);
 }
 
-/**
- * srcu_read_lock_lite - register a new reader for an SRCU-protected structure.
- * @ssp: srcu_struct in which to register the new reader.
- *
- * Enter an SRCU read-side critical section, but for a light-weight
- * smp_mb()-free reader.  See srcu_read_lock() for more information.
- *
- * If srcu_read_lock_lite() is ever used on an srcu_struct structure,
- * then none of the other flavors may be used, whether before, during,
- * or after.  Note that grace-period auto-expediting is disabled for _lite
- * srcu_struct structures because auto-expedited grace periods invoke
- * synchronize_rcu_expedited(), IPIs and all.
- *
- * Note that srcu_read_lock_lite() can be invoked only from those contexts
- * where RCU is watching, that is, from contexts where it would be legal
- * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
- */
-static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
-{
-	int retval;
-
-	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_LITE);
-	retval = __srcu_read_lock_lite(ssp);
-	rcu_try_lock_acquire(&ssp->dep_map);
-	return retval;
-}
-
 /**
  * srcu_read_lock_nmisafe - register a new reader for an SRCU-protected structure.
  * @ssp: srcu_struct in which to register the new reader.
@@ -434,22 +407,6 @@ static inline void srcu_up_read_fast(struct srcu_struct *ssp, struct srcu_ctr __
 	__srcu_read_unlock_fast(ssp, scp);
 }
 
-/**
- * srcu_read_unlock_lite - unregister a old reader from an SRCU-protected structure.
- * @ssp: srcu_struct in which to unregister the old reader.
- * @idx: return value from corresponding srcu_read_lock_lite().
- *
- * Exit a light-weight SRCU read-side critical section.
- */
-static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
-{
-	WARN_ON_ONCE(idx & ~0x1);
-	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
-	srcu_lock_release(&ssp->dep_map);
-	__srcu_read_unlock_lite(ssp, idx);
-}
-
 /**
  * srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 380260317d98b..51ce25f07930e 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -93,9 +93,6 @@ static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_
 	__srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp));
 }
 
-#define __srcu_read_lock_lite __srcu_read_lock
-#define __srcu_read_unlock_lite __srcu_read_unlock
-
 static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
 {
 	synchronize_srcu(ssp);
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 8bed7e6cc4c1f..bf44d8d1e69ea 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -278,44 +278,6 @@ static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
 }
 
-/*
- * Counts the new reader in the appropriate per-CPU element of the
- * srcu_struct.  Returns an index that must be passed to the matching
- * srcu_read_unlock_lite().
- *
- * Note that this_cpu_inc() is an RCU read-side critical section either
- * because it disables interrupts, because it is a single instruction,
- * or because it is a read-modify-write atomic operation, depending on
- * the whims of the architecture.
- */
-static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
-{
-	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
-
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite().");
-	this_cpu_inc(scp->srcu_locks.counter); /* Y */
-	barrier(); /* Avoid leaking the critical section. */
-	return __srcu_ptr_to_ctr(ssp, scp);
-}
-
-/*
- * Removes the count for the old reader from the appropriate
- * per-CPU element of the srcu_struct.  Note that this may well be a
- * different CPU than that which was incremented by the corresponding
- * srcu_read_lock_lite(), but it must be within the same task.
- *
- * Note that this_cpu_inc() is an RCU read-side critical section either
- * because it disables interrupts, because it is a single instruction,
- * or because it is a read-modify-write atomic operation, depending on
- * the whims of the architecture.
- */
-static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
-{
-	barrier();  /* Avoid leaking the critical section. */
-	this_cpu_inc(__srcu_ctr_to_ptr(ssp, idx)->srcu_unlocks.counter);  /* Z */
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite().");
-}
-
 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
 
 // Record reader usage even for CONFIG_PROVE_RCU=n kernels.  This is
-- 
2.40.1

[PATCH 5/5] checkpatch: Remove SRCU-lite deprecation

[Paul E. McKenney]

Now that SRCU-lite has been removed from the kernel, let's remove the
now-redundant deprecation from checkpatch.pl.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 scripts/checkpatch.pl | 2 --
 1 file changed, 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 664f7b7a622c2..867c7b6fd839f 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -857,8 +857,6 @@ our %deprecated_apis = (
 	"kunmap"				=> "kunmap_local",
 	"kmap_atomic"				=> "kmap_local_page",
 	"kunmap_atomic"				=> "kunmap_local",
-	"srcu_read_lock_lite"			=> "srcu_read_lock_fast",
-	"srcu_read_unlock_lite"			=> "srcu_read_unlock_fast",
 );
 
 #Create a search pattern for all these strings to speed up a loop below
-- 
2.40.1

[PATCH v2 0/5] Remove SRCU-lite in favor of SRCU-fast

[Paul E. McKenney]

Hello!

This series removes the deprecated SRCU-lite flavor.

Both SRCU-lite and SRCU-fast provide faster readers by dropping the
smp_mb() call from their lock and unlock primitives.  The price of this
is a pair of added RCU grace periods during the SRCU grace period.

SRCU-fast also adds NMI safety for architectures that have NMIs but do
not have NMI-safe per-CPU operations.  In addition, srcu_read_lock_fast()
returns a per-CPU pointer rather than an integer, which provides a further
speedup compared to SRCU-lite by getting rid of array-index calculations.

There is a trivial mapping from the SRCU-lite API to that of SRCU-fast,
so we do not expect any transition issues.  In addition, while SRCU-lite
remains in the kernel, checkpatch.pl will warn about added SRCU-lite
use cases.

Further read-side speedups are possible, but they amount to only about
half a nanosecond out of about two nanoseconds (measured on my x86
laptop), and they might require some changes to existing SRCU code.
These changes are trivial, but we need to see a solid need for the
additional performance before inconveniencing existing users.

1.	Remove support for SRCU-lite.

2.	Remove SRCU-lite scenarios.

3.	Remove support for SRCU-lite.

4.	Remove SRCU-lite implementation.

5.	Remove SRCU-lite deprecation.


Changes since v1:

o	Add short explanation of SRCU-lite and SRCU-fast.

						Thanx, Paul

------------------------------------------------------------------------

 b/include/linux/srcu.h                                     |    2 
 b/include/linux/srcutiny.h                                 |    3 
 b/include/linux/srcutree.h                                 |   38 ----------
 b/kernel/rcu/rcutorture.c                                  |    7 -
 b/kernel/rcu/refscale.c                                    |   32 --------
 b/scripts/checkpatch.pl                                    |    2 
 b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST    |    1 
 include/linux/srcu.h                                       |   47 -------------
 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L      |   10 --
 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot |    3 
 10 files changed, 4 insertions(+), 141 deletions(-)

[PATCH v2 1/5] torture: Remove support for SRCU-lite

[Paul E. McKenney]

Because SRCU-lite is being replaced by SRCU-fast, this commit removes
support for SRCU-lite from refscale.c.

Both SRCU-lite and SRCU-fast provide faster readers by dropping the
smp_mb() call from their lock and unlock primitives, but incur a pair
of added RCU grace periods during the SRCU grace period.  There is a
trivial mapping from the SRCU-lite API to that of SRCU-fast, so there
should be no transition issues.

[ paulmck: Apply Christoph Hellwig feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/refscale.c | 32 +-------------------------------
 1 file changed, 1 insertion(+), 31 deletions(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index f11a7c2af778c..f4b2cea1cce5e 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -246,36 +246,6 @@ static const struct ref_scale_ops srcu_fast_ops = {
 	.name		= "srcu-fast"
 };
 
-static void srcu_lite_ref_scale_read_section(const int nloops)
-{
-	int i;
-	int idx;
-
-	for (i = nloops; i >= 0; i--) {
-		idx = srcu_read_lock_lite(srcu_ctlp);
-		srcu_read_unlock_lite(srcu_ctlp, idx);
-	}
-}
-
-static void srcu_lite_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
-{
-	int i;
-	int idx;
-
-	for (i = nloops; i >= 0; i--) {
-		idx = srcu_read_lock_lite(srcu_ctlp);
-		un_delay(udl, ndl);
-		srcu_read_unlock_lite(srcu_ctlp, idx);
-	}
-}
-
-static const struct ref_scale_ops srcu_lite_ops = {
-	.init		= rcu_sync_scale_init,
-	.readsection	= srcu_lite_ref_scale_read_section,
-	.delaysection	= srcu_lite_ref_scale_delay_section,
-	.name		= "srcu-lite"
-};
-
 #ifdef CONFIG_TASKS_RCU
 
 // Definitions for RCU Tasks ref scale testing: Empty read markers.
@@ -1193,7 +1163,7 @@ ref_scale_init(void)
 	long i;
 	int firsterr = 0;
 	static const struct ref_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &srcu_fast_ops, &srcu_lite_ops, RCU_TRACE_OPS RCU_TASKS_OPS
+		&rcu_ops, &srcu_ops, &srcu_fast_ops, RCU_TRACE_OPS RCU_TASKS_OPS
 		&refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops,
 		&acqrel_ops, &sched_clock_ops, &clock_ops, &jiffies_ops,
 		&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
-- 
2.40.1

[PATCH v2 2/5] rcutorture: Remove SRCU-lite scenarios

[Paul E. McKenney]

This commit prepares for the removal of SRCU-Lite by removing the SRCU-L
rcutorture scenario that tests it.

Both SRCU-lite and SRCU-fast provide faster readers by dropping the
smp_mb() call from their lock and unlock primitives, but incur a pair
of added RCU grace periods during the SRCU grace period.  There is a
trivial mapping from the SRCU-lite API to that of SRCU-fast, so there
should be no transition issues.

[ paulmck: Apply Christoph Hellwig feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 tools/testing/selftests/rcutorture/configs/rcu/CFLIST  |  1 -
 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L  | 10 ----------
 .../selftests/rcutorture/configs/rcu/SRCU-L.boot       |  3 ---
 3 files changed, 14 deletions(-)
 delete mode 100644 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
 delete mode 100644 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot

diff --git a/tools/testing/selftests/rcutorture/configs/rcu/CFLIST b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
index 45f572570a8c3..98b6175e5aa09 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
+++ b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
@@ -5,7 +5,6 @@ TREE04
 TREE05
 TREE07
 TREE09
-SRCU-L
 SRCU-N
 SRCU-P
 SRCU-T
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
deleted file mode 100644
index 3b4fa8dbef8a9..0000000000000
--- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
+++ /dev/null
@@ -1,10 +0,0 @@
-CONFIG_RCU_TRACE=n
-CONFIG_SMP=y
-CONFIG_NR_CPUS=6
-CONFIG_HOTPLUG_CPU=y
-CONFIG_PREEMPT_NONE=y
-CONFIG_PREEMPT_VOLUNTARY=n
-CONFIG_PREEMPT=n
-#CHECK#CONFIG_RCU_EXPERT=n
-CONFIG_KPROBES=n
-CONFIG_FTRACE=n
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot
deleted file mode 100644
index 0207b3138c5be..0000000000000
--- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot
+++ /dev/null
@@ -1,3 +0,0 @@
-rcutorture.torture_type=srcu
-rcutorture.reader_flavor=0x4
-rcutorture.fwd_progress=3
-- 
2.40.1

[PATCH v2 3/5] rcutorture: Remove support for SRCU-lite

[Paul E. McKenney]

Because SRCU-lite is being replaced by SRCU-fast, this commit removes
support for SRCU-lite from rcutorture.c

Both SRCU-lite and SRCU-fast provide faster readers by dropping the
smp_mb() call from their lock and unlock primitives, but incur a pair
of added RCU grace periods during the SRCU grace period.  There is a
trivial mapping from the SRCU-lite API to that of SRCU-fast, so there
should be no transition issues.

[ paulmck: Apply Christoph Hellwig feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/srcu.h    | 2 +-
 kernel/rcu/rcutorture.c | 7 -------
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 900b0d5c05f54..c20dacb563e55 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -49,7 +49,7 @@ int init_srcu_struct(struct srcu_struct *ssp);
 #define SRCU_READ_FLAVOR_LITE	0x4		// srcu_read_lock_lite().
 #define SRCU_READ_FLAVOR_FAST	0x8		// srcu_read_lock_fast().
 #define SRCU_READ_FLAVOR_ALL   (SRCU_READ_FLAVOR_NORMAL | SRCU_READ_FLAVOR_NMI | \
-				SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST) // All of the above.
+				SRCU_READ_FLAVOR_FAST) // All of the above.
 #define SRCU_READ_FLAVOR_SLOWGP	(SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST)
 						// Flavors requiring synchronize_rcu()
 						// instead of smp_mb().
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 213f23f20a64b..7a893d51d02b6 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -718,11 +718,6 @@ static int srcu_torture_read_lock(void)
 		WARN_ON_ONCE(idx & ~0x1);
 		ret += idx << 1;
 	}
-	if (reader_flavor & SRCU_READ_FLAVOR_LITE) {
-		idx = srcu_read_lock_lite(srcu_ctlp);
-		WARN_ON_ONCE(idx & ~0x1);
-		ret += idx << 2;
-	}
 	if (reader_flavor & SRCU_READ_FLAVOR_FAST) {
 		scp = srcu_read_lock_fast(srcu_ctlp);
 		idx = __srcu_ptr_to_ctr(srcu_ctlp, scp);
@@ -756,8 +751,6 @@ static void srcu_torture_read_unlock(int idx)
 	WARN_ON_ONCE((reader_flavor && (idx & ~reader_flavor)) || (!reader_flavor && (idx & ~0x1)));
 	if (reader_flavor & SRCU_READ_FLAVOR_FAST)
 		srcu_read_unlock_fast(srcu_ctlp, __srcu_ctr_to_ptr(srcu_ctlp, (idx & 0x8) >> 3));
-	if (reader_flavor & SRCU_READ_FLAVOR_LITE)
-		srcu_read_unlock_lite(srcu_ctlp, (idx & 0x4) >> 2);
 	if (reader_flavor & SRCU_READ_FLAVOR_NMI)
 		srcu_read_unlock_nmisafe(srcu_ctlp, (idx & 0x2) >> 1);
 	if ((reader_flavor & SRCU_READ_FLAVOR_NORMAL) || !(reader_flavor & SRCU_READ_FLAVOR_ALL))
-- 
2.40.1

[PATCH v2 4/5] srcu: Remove SRCU-lite implementation

[Paul E. McKenney]

This commit removes the SRCU-lite implementation, which has been replaced
by SRCU-fast.

Both SRCU-lite and SRCU-fast provide faster readers by dropping the
smp_mb() call from their lock and unlock primitives, but incur a pair
of added RCU grace periods during the SRCU grace period.  There is a
trivial mapping from the SRCU-lite API to that of SRCU-fast, so there
should be no transition issues.

[ paulmck: Apply Christoph Hellwig feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/srcu.h     | 47 ++--------------------------------------
 include/linux/srcutiny.h |  3 ---
 include/linux/srcutree.h | 38 --------------------------------
 3 files changed, 2 insertions(+), 86 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index c20dacb563e55..cf711a0f440b2 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -46,11 +46,11 @@ int init_srcu_struct(struct srcu_struct *ssp);
 /* Values for SRCU Tree srcu_data ->srcu_reader_flavor, but also used by rcutorture. */
 #define SRCU_READ_FLAVOR_NORMAL	0x1		// srcu_read_lock().
 #define SRCU_READ_FLAVOR_NMI	0x2		// srcu_read_lock_nmisafe().
-#define SRCU_READ_FLAVOR_LITE	0x4		// srcu_read_lock_lite().
+//				0x4		// SRCU-lite is no longer with us.
 #define SRCU_READ_FLAVOR_FAST	0x8		// srcu_read_lock_fast().
 #define SRCU_READ_FLAVOR_ALL   (SRCU_READ_FLAVOR_NORMAL | SRCU_READ_FLAVOR_NMI | \
 				SRCU_READ_FLAVOR_FAST) // All of the above.
-#define SRCU_READ_FLAVOR_SLOWGP	(SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST)
+#define SRCU_READ_FLAVOR_SLOWGP	SRCU_READ_FLAVOR_FAST
 						// Flavors requiring synchronize_rcu()
 						// instead of smp_mb().
 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
@@ -299,33 +299,6 @@ static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *
 	return __srcu_read_lock_fast(ssp);
 }
 
-/**
- * srcu_read_lock_lite - register a new reader for an SRCU-protected structure.
- * @ssp: srcu_struct in which to register the new reader.
- *
- * Enter an SRCU read-side critical section, but for a light-weight
- * smp_mb()-free reader.  See srcu_read_lock() for more information.
- *
- * If srcu_read_lock_lite() is ever used on an srcu_struct structure,
- * then none of the other flavors may be used, whether before, during,
- * or after.  Note that grace-period auto-expediting is disabled for _lite
- * srcu_struct structures because auto-expedited grace periods invoke
- * synchronize_rcu_expedited(), IPIs and all.
- *
- * Note that srcu_read_lock_lite() can be invoked only from those contexts
- * where RCU is watching, that is, from contexts where it would be legal
- * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
- */
-static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
-{
-	int retval;
-
-	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_LITE);
-	retval = __srcu_read_lock_lite(ssp);
-	rcu_try_lock_acquire(&ssp->dep_map);
-	return retval;
-}
-
 /**
  * srcu_read_lock_nmisafe - register a new reader for an SRCU-protected structure.
  * @ssp: srcu_struct in which to register the new reader.
@@ -434,22 +407,6 @@ static inline void srcu_up_read_fast(struct srcu_struct *ssp, struct srcu_ctr __
 	__srcu_read_unlock_fast(ssp, scp);
 }
 
-/**
- * srcu_read_unlock_lite - unregister a old reader from an SRCU-protected structure.
- * @ssp: srcu_struct in which to unregister the old reader.
- * @idx: return value from corresponding srcu_read_lock_lite().
- *
- * Exit a light-weight SRCU read-side critical section.
- */
-static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
-	__releases(ssp)
-{
-	WARN_ON_ONCE(idx & ~0x1);
-	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
-	srcu_lock_release(&ssp->dep_map);
-	__srcu_read_unlock_lite(ssp, idx);
-}
-
 /**
  * srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 380260317d98b..51ce25f07930e 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -93,9 +93,6 @@ static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_
 	__srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp));
 }
 
-#define __srcu_read_lock_lite __srcu_read_lock
-#define __srcu_read_unlock_lite __srcu_read_unlock
-
 static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
 {
 	synchronize_srcu(ssp);
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 8bed7e6cc4c1f..bf44d8d1e69ea 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -278,44 +278,6 @@ static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
 }
 
-/*
- * Counts the new reader in the appropriate per-CPU element of the
- * srcu_struct.  Returns an index that must be passed to the matching
- * srcu_read_unlock_lite().
- *
- * Note that this_cpu_inc() is an RCU read-side critical section either
- * because it disables interrupts, because it is a single instruction,
- * or because it is a read-modify-write atomic operation, depending on
- * the whims of the architecture.
- */
-static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
-{
-	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
-
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite().");
-	this_cpu_inc(scp->srcu_locks.counter); /* Y */
-	barrier(); /* Avoid leaking the critical section. */
-	return __srcu_ptr_to_ctr(ssp, scp);
-}
-
-/*
- * Removes the count for the old reader from the appropriate
- * per-CPU element of the srcu_struct.  Note that this may well be a
- * different CPU than that which was incremented by the corresponding
- * srcu_read_lock_lite(), but it must be within the same task.
- *
- * Note that this_cpu_inc() is an RCU read-side critical section either
- * because it disables interrupts, because it is a single instruction,
- * or because it is a read-modify-write atomic operation, depending on
- * the whims of the architecture.
- */
-static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
-{
-	barrier();  /* Avoid leaking the critical section. */
-	this_cpu_inc(__srcu_ctr_to_ptr(ssp, idx)->srcu_unlocks.counter);  /* Z */
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite().");
-}
-
 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
 
 // Record reader usage even for CONFIG_PROVE_RCU=n kernels.  This is
-- 
2.40.1

[PATCH v2 5/5] checkpatch: Remove SRCU-lite deprecation

[Paul E. McKenney]

Now that SRCU-lite has been removed from the kernel, let's remove the
now-redundant deprecation from checkpatch.pl.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 scripts/checkpatch.pl | 2 --
 1 file changed, 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 664f7b7a622c2..867c7b6fd839f 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -857,8 +857,6 @@ our %deprecated_apis = (
 	"kunmap"				=> "kunmap_local",
 	"kmap_atomic"				=> "kmap_local_page",
 	"kunmap_atomic"				=> "kunmap_local",
-	"srcu_read_lock_lite"			=> "srcu_read_lock_fast",
-	"srcu_read_unlock_lite"			=> "srcu_read_unlock_fast",
 );
 
 #Create a search pattern for all these strings to speed up a loop below
-- 
2.40.1