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Subject[PATCH -rcu dev 1/2] Revert b8c17e6664c4 ("rcu: Maintain special bits at bottom of ->dynticks counter")
Date
This code is unused and can be removed now. Revert was straightforward.

Tested with light rcutorture.

Link: http://lore.kernel.org/r/CALCETrWNPOOdTrFabTDd=H7+wc6xJ9rJceg6OL1S0rTV5pfSsA@mail.gmail.com
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

---
include/linux/rcutiny.h | 3 --
kernel/rcu/tree.c | 82 ++++++++++-------------------------------
2 files changed, 19 insertions(+), 66 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index b7607e2667ae..b3f689711289 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -14,9 +14,6 @@

#include <asm/param.h> /* for HZ */

-/* Never flag non-existent other CPUs! */
-static inline bool rcu_eqs_special_set(int cpu) { return false; }
-
static inline unsigned long get_state_synchronize_rcu(void)
{
return 0;
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 68ebf0eb64c8..417dd00b9e87 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -69,20 +69,10 @@

/* Data structures. */

-/*
- * Steal a bit from the bottom of ->dynticks for idle entry/exit
- * control. Initially this is for TLB flushing.
- */
-#define RCU_DYNTICK_CTRL_MASK 0x1
-#define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
-#ifndef rcu_eqs_special_exit
-#define rcu_eqs_special_exit() do { } while (0)
-#endif
-
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
.dynticks_nesting = 1,
.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
- .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
+ .dynticks = ATOMIC_INIT(1),
};
struct rcu_state rcu_state = {
.level = { &rcu_state.node[0] },
@@ -229,20 +219,15 @@ void rcu_softirq_qs(void)
static void rcu_dynticks_eqs_enter(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
- int seq;
+ int special;

/*
- * CPUs seeing atomic_add_return() must see prior RCU read-side
+ * CPUs seeing atomic_inc_return() must see prior RCU read-side
* critical sections, and we also must force ordering with the
* next idle sojourn.
*/
- seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
- /* Better be in an extended quiescent state! */
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- (seq & RCU_DYNTICK_CTRL_CTR));
- /* Better not have special action (TLB flush) pending! */
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- (seq & RCU_DYNTICK_CTRL_MASK));
+ special = atomic_inc_return(&rdp->dynticks);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && special & 0x1);
}

/*
@@ -252,22 +237,15 @@ static void rcu_dynticks_eqs_enter(void)
static void rcu_dynticks_eqs_exit(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
- int seq;
+ int special;

/*
- * CPUs seeing atomic_add_return() must see prior idle sojourns,
+ * CPUs seeing atomic_inc_return() must see prior idle sojourns,
* and we also must force ordering with the next RCU read-side
* critical section.
*/
- seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- !(seq & RCU_DYNTICK_CTRL_CTR));
- if (seq & RCU_DYNTICK_CTRL_MASK) {
- atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
- smp_mb__after_atomic(); /* _exit after clearing mask. */
- /* Prefer duplicate flushes to losing a flush. */
- rcu_eqs_special_exit();
- }
+ special = atomic_inc_return(&rdp->dynticks);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(special & 0x1));
}

/*
@@ -284,9 +262,9 @@ static void rcu_dynticks_eqs_online(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);

- if (atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR)
+ if (atomic_read(&rdp->dynticks) & 0x1)
return;
- atomic_add(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
+ atomic_add(0x1, &rdp->dynticks);
}

/*
@@ -298,7 +276,7 @@ bool rcu_dynticks_curr_cpu_in_eqs(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);

- return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
+ return !(atomic_read(&rdp->dynticks) & 0x1);
}

/*
@@ -309,7 +287,7 @@ int rcu_dynticks_snap(struct rcu_data *rdp)
{
int snap = atomic_add_return(0, &rdp->dynticks);

- return snap & ~RCU_DYNTICK_CTRL_MASK;
+ return snap;
}

/*
@@ -318,7 +296,7 @@ int rcu_dynticks_snap(struct rcu_data *rdp)
*/
static bool rcu_dynticks_in_eqs(int snap)
{
- return !(snap & RCU_DYNTICK_CTRL_CTR);
+ return !(snap & 0x1);
}

/*
@@ -331,28 +309,6 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
return snap != rcu_dynticks_snap(rdp);
}

-/*
- * Set the special (bottom) bit of the specified CPU so that it
- * will take special action (such as flushing its TLB) on the
- * next exit from an extended quiescent state. Returns true if
- * the bit was successfully set, or false if the CPU was not in
- * an extended quiescent state.
- */
-bool rcu_eqs_special_set(int cpu)
-{
- int old;
- int new;
- struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
-
- do {
- old = atomic_read(&rdp->dynticks);
- if (old & RCU_DYNTICK_CTRL_CTR)
- return false;
- new = old | RCU_DYNTICK_CTRL_MASK;
- } while (atomic_cmpxchg(&rdp->dynticks, old, new) != old);
- return true;
-}
-
/*
* Let the RCU core know that this CPU has gone through the scheduler,
* which is a quiescent state. This is called when the need for a
@@ -366,13 +322,13 @@ bool rcu_eqs_special_set(int cpu)
*/
void rcu_momentary_dyntick_idle(void)
{
- int special;
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+ int special = atomic_add_return(2, &rdp->dynticks);

- raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
- special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
- &this_cpu_ptr(&rcu_data)->dynticks);
/* It is illegal to call this from idle state. */
- WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
+ WARN_ON_ONCE(!(special & 0x1));
+
+ raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
rcu_preempt_deferred_qs(current);
}
EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
--
2.23.0.187.g17f5b7556c-goog
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