x86/entry: Clean up idtentry_enter/exit() leftovers

Now that everything is converted to conditional RCU handling remove
idtentry_enter/exit() and tidy up the conditional functions.

This does not remove rcu_irq_exit_preempt(), to avoid conflicts with the RCU
tree. Will be removed once all of this hits Linus's tree.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202117.473597954@linutronix.de

arch/x86/entry/common.c

@@ -515,7 +515,6 @@ SYSCALL_DEFINE0(ni_syscall)
  * idtentry_enter_cond_rcu - Handle state tracking on idtentry with conditional
  *			     RCU handling
  * @regs:	Pointer to pt_regs of interrupted context
- * @cond_rcu:	Invoke rcu_irq_enter() only if RCU is not watching
  *
  * Invokes:
  *  - lockdep irqflag state tracking as low level ASM entry disabled
@@ -545,14 +544,14 @@ SYSCALL_DEFINE0(ni_syscall)
  * The return value must be fed into the rcu_exit argument of
  * idtentry_exit_cond_rcu().
  */
-bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs, bool cond_rcu)
+bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
 		enter_from_user_mode();
 		return false;
 	}
 
-	if (!cond_rcu || !__rcu_is_watching()) {
+	if (!__rcu_is_watching()) {
 		/*
 		 * If RCU is not watching then the same careful
 		 * sequence vs. lockdep and tracing is required
@@ -608,52 +607,44 @@ void noinstr idtentry_exit_cond_rcu(struct pt_regs *regs, bool rcu_exit)
 	if (user_mode(regs)) {
 		prepare_exit_to_usermode(regs);
 	} else if (regs->flags & X86_EFLAGS_IF) {
-		/* Check kernel preemption, if enabled */
-		if (IS_ENABLED(CONFIG_PREEMPTION)) {
 		/*
-			 * This needs to be done very carefully.
-			 * idtentry_enter() invoked rcu_irq_enter(). This
-			 * needs to be undone before scheduling.
-			 *
-			 * Preemption is disabled inside of RCU idle
-			 * sections. When the task returns from
-			 * preempt_schedule_irq(), RCU is still watching.
-			 *
-			 * rcu_irq_exit_preempt() has additional state
-			 * checking if CONFIG_PROVE_RCU=y
-			 */
-			if (!preempt_count()) {
-				if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
-					WARN_ON_ONCE(!on_thread_stack());
-				instrumentation_begin();
-				if (rcu_exit)
-					rcu_irq_exit_preempt();
-				if (need_resched())
-					preempt_schedule_irq();
-				/* Covers both tracing and lockdep */
-				trace_hardirqs_on();
-				instrumentation_end();
-				return;
-			}
-		}
-		/*
-		 * If preemption is disabled then this needs to be done
-		 * carefully with respect to RCU. The exception might come
-		 * from a RCU idle section in the idle task due to the fact
-		 * that safe_halt() enables interrupts. So this needs the
-		 * same ordering of lockdep/tracing and RCU as the return
-		 * to user mode path.
+		 * If RCU was not watching on entry this needs to be done
+		 * carefully and needs the same ordering of lockdep/tracing
+		 * and RCU as the return to user mode path.
 		 */
+		if (rcu_exit) {
 			instrumentation_begin();
 			/* Tell the tracer that IRET will enable interrupts */
 			trace_hardirqs_on_prepare();
 			lockdep_hardirqs_on_prepare(CALLER_ADDR0);
 			instrumentation_end();
-		if (rcu_exit)
 			rcu_irq_exit();
 			lockdep_hardirqs_on(CALLER_ADDR0);
+			return;
+		}
+
+		instrumentation_begin();
+
+		/* Check kernel preemption, if enabled */
+		if (IS_ENABLED(CONFIG_PREEMPTION)) {
+			if (!preempt_count()) {
+				/* Sanity check RCU and thread stack */
+				rcu_irq_exit_check_preempt();
+				if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
+					WARN_ON_ONCE(!on_thread_stack());
+				if (need_resched())
+					preempt_schedule_irq();
+			}
+		}
+		/* Covers both tracing and lockdep */
+		trace_hardirqs_on();
+
+		instrumentation_end();
 	} else {
-		/* IRQ flags state is correct already. Just tell RCU. */
+		/*
+		 * IRQ flags state is correct already. Just tell RCU if it
+		 * was not watching on entry.
+		 */
 		if (rcu_exit)
 			rcu_irq_exit();
 	}

arch/x86/include/asm/idtentry.h

@@ -10,19 +10,9 @@
 void idtentry_enter_user(struct pt_regs *regs);
 void idtentry_exit_user(struct pt_regs *regs);
 
-bool idtentry_enter_cond_rcu(struct pt_regs *regs, bool cond_rcu);
+bool idtentry_enter_cond_rcu(struct pt_regs *regs);
 void idtentry_exit_cond_rcu(struct pt_regs *regs, bool rcu_exit);
 
-static __always_inline void idtentry_enter(struct pt_regs *regs)
-{
-	idtentry_enter_cond_rcu(regs, false);
-}
-
-static __always_inline void idtentry_exit(struct pt_regs *regs)
-{
-	idtentry_exit_cond_rcu(regs, true);
-}
-
 /**
  * DECLARE_IDTENTRY - Declare functions for simple IDT entry points
  *		      No error code pushed by hardware