[PATCH v3 1/5] Revert b8c17e6664c4 ("rcu: Maintain special bits at bottom of ->dynticks counter")
From: Joel Fernandes (Google)
Date: Mon May 04 2020 - 08:05:22 EST
This code is unused and can be removed now. Revert was straightforward.
Tested with rcutorture on all TREE configurations.
Link: http://lore.kernel.org/r/CALCETrWNPOOdTrFabTDd=H7+wc6xJ9rJceg6OL1S0rTV5pfSsA@xxxxxxxxxxxxxx
Suggested-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
---
include/linux/rcutiny.h | 3 --
kernel/rcu/tree.c | 93 +++++++++++------------------------------
2 files changed, 24 insertions(+), 72 deletions(-)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 3465ba704a111..dbcddc7b26b94 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 6d39485f7f517..1ec7b1d4a03c4 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -82,20 +82,10 @@
/* 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),
};
static struct rcu_state rcu_state = {
.level = { &rcu_state.node[0] },
@@ -245,21 +235,18 @@ 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;
+
+ rcu_dynticks_task_trace_enter(); // Before ->dynticks update!
/*
- * 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.
*/
- rcu_dynticks_task_trace_enter(); // Before ->dynticks update!
- seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
+ special = atomic_inc_return(&rdp->dynticks);
// RCU is no longer watching. Better be in 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));
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && special & 0x1);
}
/*
@@ -270,24 +257,18 @@ 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);
+ special = atomic_inc_return(&rdp->dynticks);
// RCU is now watching. Better not be in an extended quiescent state!
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(special & 0x1));
+
rcu_dynticks_task_trace_exit(); // After ->dynticks update!
- 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();
- }
}
/*
@@ -304,9 +285,9 @@ 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);
}
/*
@@ -318,7 +299,7 @@ static 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);
}
/*
@@ -329,7 +310,7 @@ static int rcu_dynticks_snap(struct rcu_data *rdp)
{
int snap = atomic_add_return(0, &rdp->dynticks);
- return snap & ~RCU_DYNTICK_CTRL_MASK;
+ return snap;
}
/*
@@ -338,7 +319,7 @@ static 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);
}
/*
@@ -361,8 +342,7 @@ bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
int snap;
// If not quiescent, force back to earlier extended quiescent state.
- snap = atomic_read(&rdp->dynticks) & ~(RCU_DYNTICK_CTRL_MASK |
- RCU_DYNTICK_CTRL_CTR);
+ snap = atomic_read(&rdp->dynticks) & ~(0x1);
smp_rmb(); // Order ->dynticks and *vp reads.
if (READ_ONCE(*vp))
@@ -370,32 +350,7 @@ bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
smp_rmb(); // Order *vp read and ->dynticks re-read.
// If still in the same extended quiescent state, we are good!
- return snap == (atomic_read(&rdp->dynticks) & ~RCU_DYNTICK_CTRL_MASK);
-}
-
-/*
- * 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;
- int new_old;
- struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
-
- new_old = atomic_read(&rdp->dynticks);
- do {
- old = new_old;
- if (old & RCU_DYNTICK_CTRL_CTR)
- return false;
- new = old | RCU_DYNTICK_CTRL_MASK;
- new_old = atomic_cmpxchg(&rdp->dynticks, old, new);
- } while (new_old != old);
- return true;
+ return snap == atomic_read(&rdp->dynticks);
}
/*
@@ -411,13 +366,13 @@ 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);
--
2.26.2.526.g744177e7f7-goog