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Message-Id: <20250624161400.867880-4-paulmck@kernel.org>
Date: Tue, 24 Jun 2025 09:13:59 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
kernel-team@...a.com,
rostedt@...dmis.org,
"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH 4/5] srcu: Remove SRCU-lite implementation
This commit removes the SRCU-lite implementation, which has been replaced
by SRCU-fast.
Signed-off-by: Paul E. McKenney <paulmck@...nel.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
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