context_tracking: Convert state to atomic_t

Context tracking's state and dynticks counter are going to be merged
in a single field so that both updates can happen atomically and at the
same time. Prepare for that with converting the state into an atomic_t.

[ paulmck: Apply kernel test robot feedback. ]
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>

include/linux/context_tracking.h

@@ -56,7 +56,7 @@ static inline enum ctx_state exception_enter(void)
 	    !context_tracking_enabled())
 		return 0;
 
-	prev_ctx = this_cpu_read(context_tracking.state);
+	prev_ctx = __ct_state();
 	if (prev_ctx != CONTEXT_KERNEL)
 		ct_user_exit(prev_ctx);
 
@@ -86,33 +86,21 @@ static __always_inline void context_tracking_guest_exit(void)
 		__ct_user_exit(CONTEXT_GUEST);
 }
 
-/**
- * ct_state() - return the current context tracking state if known
- *
- * Returns the current cpu's context tracking state if context tracking
- * is enabled.  If context tracking is disabled, returns
- * CONTEXT_DISABLED.  This should be used primarily for debugging.
- */
-static __always_inline enum ctx_state ct_state(void)
-{
-	return context_tracking_enabled() ?
-		this_cpu_read(context_tracking.state) : CONTEXT_DISABLED;
-}
+#define CT_WARN_ON(cond) WARN_ON(context_tracking_enabled() && (cond))
+
 #else
 static inline void user_enter(void) { }
 static inline void user_exit(void) { }
 static inline void user_enter_irqoff(void) { }
 static inline void user_exit_irqoff(void) { }
-static inline enum ctx_state exception_enter(void) { return 0; }
+static inline int exception_enter(void) { return 0; }
 static inline void exception_exit(enum ctx_state prev_ctx) { }
-static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }
+static inline int ct_state(void) { return -1; }
 static __always_inline bool context_tracking_guest_enter(void) { return false; }
 static inline void context_tracking_guest_exit(void) { }
-
+#define CT_WARN_ON(cond) do { } while (0)
 #endif /* !CONFIG_CONTEXT_TRACKING_USER */
 
-#define CT_WARN_ON(cond) WARN_ON(context_tracking_enabled() && (cond))
-
 #ifdef CONFIG_CONTEXT_TRACKING_USER_FORCE
 extern void context_tracking_init(void);
 #else
@@ -130,16 +118,16 @@ extern void ct_idle_exit(void);
  */
 static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
 {
-	return !(arch_atomic_read(this_cpu_ptr(&context_tracking.dynticks)) & 0x1);
+	return !(arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & RCU_DYNTICKS_IDX);
 }
 
 /*
- * Increment the current CPU's context_tracking structure's ->dynticks field
+ * Increment the current CPU's context_tracking structure's ->state field
  * with ordering.  Return the new value.
  */
-static __always_inline unsigned long rcu_dynticks_inc(int incby)
+static __always_inline unsigned long ct_state_inc(int incby)
 {
-	return arch_atomic_add_return(incby, this_cpu_ptr(&context_tracking.dynticks));
+	return arch_atomic_add_return(incby, this_cpu_ptr(&context_tracking.state));
 }
 
 #else

include/linux/context_tracking_state.h

@@ -6,15 +6,23 @@
 #include <linux/static_key.h>
 #include <linux/context_tracking_irq.h>
 
+/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */
+#define DYNTICK_IRQ_NONIDLE	((LONG_MAX / 2) + 1)
+
 enum ctx_state {
-	CONTEXT_DISABLED = -1,	/* returned by ct_state() if unknown */
-	CONTEXT_KERNEL = 0,
-	CONTEXT_USER,
-	CONTEXT_GUEST,
+	CONTEXT_DISABLED	= -1,	/* returned by ct_state() if unknown */
+	CONTEXT_KERNEL		= 0,
+	CONTEXT_IDLE		= 1,
+	CONTEXT_USER		= 2,
+	CONTEXT_GUEST		= 3,
+	CONTEXT_MAX		= 4,
 };
 
-/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */
-#define DYNTICK_IRQ_NONIDLE	((LONG_MAX / 2) + 1)
+/* Even value for idle, else odd. */
+#define RCU_DYNTICKS_IDX CONTEXT_MAX
+
+#define CT_STATE_MASK (CONTEXT_MAX - 1)
+#define CT_DYNTICKS_MASK (~CT_STATE_MASK)
 
 struct context_tracking {
 #ifdef CONFIG_CONTEXT_TRACKING_USER
@@ -26,10 +34,11 @@ struct context_tracking {
 	 */
 	bool active;
 	int recursion;
-	enum ctx_state state;
+#endif
+#ifdef CONFIG_CONTEXT_TRACKING
+	atomic_t state;
 #endif
 #ifdef CONFIG_CONTEXT_TRACKING_IDLE
-	atomic_t dynticks;		/* Even value for idle, else odd. */
 	long dynticks_nesting;		/* Track process nesting level. */
 	long dynticks_nmi_nesting;	/* Track irq/NMI nesting level. */
 #endif
@@ -37,26 +46,31 @@ struct context_tracking {
 
 #ifdef CONFIG_CONTEXT_TRACKING
 DECLARE_PER_CPU(struct context_tracking, context_tracking);
+
+static __always_inline int __ct_state(void)
+{
+	return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
+}
 #endif
 
 #ifdef CONFIG_CONTEXT_TRACKING_IDLE
 static __always_inline int ct_dynticks(void)
 {
-	return atomic_read(this_cpu_ptr(&context_tracking.dynticks));
+	return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_DYNTICKS_MASK;
 }
 
 static __always_inline int ct_dynticks_cpu(int cpu)
 {
 	struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
 
-	return atomic_read(&ct->dynticks);
+	return atomic_read(&ct->state) & CT_DYNTICKS_MASK;
 }
 
 static __always_inline int ct_dynticks_cpu_acquire(int cpu)
 {
 	struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
 
-	return atomic_read_acquire(&ct->dynticks);
+	return atomic_read_acquire(&ct->state) & CT_DYNTICKS_MASK;
 }
 
 static __always_inline long ct_dynticks_nesting(void)
@@ -102,6 +116,27 @@ static inline bool context_tracking_enabled_this_cpu(void)
 	return context_tracking_enabled() && __this_cpu_read(context_tracking.active);
 }
 
+/**
+ * ct_state() - return the current context tracking state if known
+ *
+ * Returns the current cpu's context tracking state if context tracking
+ * is enabled.  If context tracking is disabled, returns
+ * CONTEXT_DISABLED.  This should be used primarily for debugging.
+ */
+static __always_inline int ct_state(void)
+{
+	int ret;
+
+	if (!context_tracking_enabled())
+		return CONTEXT_DISABLED;
+
+	preempt_disable();
+	ret = __ct_state();
+	preempt_enable();
+
+	return ret;
+}
+
 #else
 static __always_inline bool context_tracking_enabled(void) { return false; }
 static __always_inline bool context_tracking_enabled_cpu(int cpu) { return false; }

kernel/rcu/tree.c

@@ -272,9 +272,9 @@ void rcu_softirq_qs(void)
  */
 static void rcu_dynticks_eqs_online(void)
 {
-	if (ct_dynticks() & 0x1)
+	if (ct_dynticks() & RCU_DYNTICKS_IDX)
 		return;
-	rcu_dynticks_inc(1);
+	ct_state_inc(RCU_DYNTICKS_IDX);
 }
 
 /*
@@ -293,7 +293,7 @@ static int rcu_dynticks_snap(int cpu)
  */
 static bool rcu_dynticks_in_eqs(int snap)
 {
-	return !(snap & 0x1);
+	return !(snap & RCU_DYNTICKS_IDX);
 }
 
 /* Return true if the specified CPU is currently idle from an RCU viewpoint.  */
@@ -321,8 +321,7 @@ bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
 	int snap;
 
 	// If not quiescent, force back to earlier extended quiescent state.
-	snap = ct_dynticks_cpu(cpu) & ~0x1;
-
+	snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX;
 	smp_rmb(); // Order ->dynticks and *vp reads.
 	if (READ_ONCE(*vp))
 		return false;  // Non-zero, so report failure;
@@ -348,9 +347,9 @@ notrace void rcu_momentary_dyntick_idle(void)
 	int seq;
 
 	raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
-	seq = rcu_dynticks_inc(2);
+	seq = ct_state_inc(2 * RCU_DYNTICKS_IDX);
 	/* It is illegal to call this from idle state. */
-	WARN_ON_ONCE(!(seq & 0x1));
+	WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX));
 	rcu_preempt_deferred_qs(current);
 }
 EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);

kernel/rcu/tree_stall.h

@@ -469,7 +469,7 @@ static void print_cpu_stall_info(int cpu)
 	rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);
 	if (rcuc_starved)
 		sprintf(buf, " rcuc=%ld jiffies(starved)", j);
-	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
+	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
 	       cpu,
 	       "O."[!!cpu_online(cpu)],
 	       "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
@@ -478,7 +478,7 @@ static void print_cpu_stall_info(int cpu)
 			rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
 				"!."[!delta],
 	       ticks_value, ticks_title,
-	       rcu_dynticks_snap(cpu) & 0xfff,
+	       rcu_dynticks_snap(cpu) & 0xffff,
 	       ct_dynticks_nesting_cpu(cpu), ct_dynticks_nmi_nesting_cpu(cpu),
 	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
 	       data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,