linux-kernel - [PATCH 07/14] x86: Use lockdep to assert IRQs are disabled/enabled

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Date:   Mon,  6 Nov 2017 16:01:23 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Tejun Heo <tj@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S . Miller" <davem@...emloft.net>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH 07/14] x86: Use lockdep to assert IRQs are disabled/enabled

Use lockdep to check that IRQs are enabled or disabled as expected. This
way the sanity check only shows overhead when concurrency correctness
debug code is enabled.

It also makes no more sense to fix the IRQ flags when a bug is detected
as the assertion is now pure config-dependent debugging. And to quote
Peter Zijlstra:

	The whole if !disabled, disable logic is uber paranoid programming,
	but I don't think we've ever seen that WARN trigger, and if it does
	(and then burns the kernel) we at least know what happend.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 arch/x86/entry/common.c   | 4 +---
 arch/x86/kernel/smpboot.c | 2 +-
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index eaa0ba6..d7d3cc2 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -186,9 +186,7 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 
 	addr_limit_user_check();
 
-	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
-		local_irq_disable();
-
+	lockdep_assert_irqs_disabled();
 	lockdep_sys_exit();
 
 	cached_flags = READ_ONCE(ti->flags);
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 198416d..4008b6b 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1095,7 +1095,7 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 	unsigned long flags;
 	int err, ret = 0;
 
-	WARN_ON(irqs_disabled());
+	lockdep_assert_irqs_enabled();
 
 	pr_debug("++++++++++++++++++++=_---CPU UP  %u\n", cpu);
 
-- 
2.7.4