[PATCH v2 2/5] irq: Add {over,under}flow detection for local_interrupt_{enable,disable}

[Boqun Feng <boqun@kernel.org>]

Currently there is no way to detect overflow and underflow inside the
HARDIRQ_DISABLE_MASK part of preempt_count. Add these detection guarded
by DEBUG_PREEMPT similar to the detection for PREEMPT_MASK
{over,under}flow.

Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 include/linux/interrupt_rc.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/interrupt_rc.h b/include/linux/interrupt_rc.h
index a9ed937a80e7..d385ab05a2b6 100644
--- a/include/linux/interrupt_rc.h
+++ b/include/linux/interrupt_rc.h
@@ -11,6 +11,7 @@
  * make it easier to include without hitting circular header dependencies.
  */
 
+#include <linux/debug_locks.h>
 #include <linux/irqflags.h>
 #include <linux/preempt.h>
 #include <linux/processor.h>
@@ -65,6 +66,13 @@ static inline void local_interrupt_disable(void)
 	local_irq_save(flags);
 	new_count = hardirq_disable_enter();
 
+	/* Is hardirq disable count overflow soon? */
+	if (IS_ENABLED(CONFIG_DEBUG_PREEMPT) &&
+	    DEBUG_LOCKS_WARN_ON(((new_count & HARDIRQ_DISABLE_MASK) +
+				 (10 << HARDIRQ_DISABLE_SHIFT)) >=
+				HARDIRQ_DISABLE_MASK))
+		return;
+
 	if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET)
 		_local_interrupt_save_state(flags);
 }
@@ -73,6 +81,11 @@ static inline void local_interrupt_enable(void)
 {
 	int new_count;
 
+	/* Unpaired local_interrupt_enable()? Warn and abort. */
+	if (IS_ENABLED(CONFIG_DEBUG_PREEMPT) &&
+	    DEBUG_LOCKS_WARN_ON((preempt_count() & HARDIRQ_DISABLE_MASK) == 0))
+		return;
+
 	new_count = hardirq_disable_exit();
 
 	if ((new_count & HARDIRQ_DISABLE_MASK) == 0)
-- 
2.51.0