[PATCH v2 5/6] locking/lockdep: Decrement irq context counters when removing lock chain

[Waiman Long]

There are currently three counters to track the irq context of a lock
chain - nr_hardirq_chains, nr_softirq_chains and nr_process_chains.
They are incremented when a new lock chain is added, but they are
not decremented when a lock chain is removed. That causes some of the
statistic counts reported by /proc/lockdep_stats to be incorrect.

Fix that by decrementing the right counter when a lock chain is removed.

Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 kernel/locking/lockdep.c           | 35 +++++++++++++++++++++---------
 kernel/locking/lockdep_internals.h |  6 +++++
 2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index f7dcd4e77a70..4ea23bb6f8d3 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2300,16 +2300,24 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
 	return 0;
 }
 
-static void inc_chains(void)
+static void inc_chains(int irq_context)
 {
-	if (current->hardirq_context)
+	if (irq_context & LOCK_CHAIN_HARDIRQ_CONTEXT)
 		nr_hardirq_chains++;
-	else {
-		if (current->softirq_context)
-			nr_softirq_chains++;
-		else
-			nr_process_chains++;
-	}
+	else if (irq_context & LOCK_CHAIN_SOFTIRQ_CONTEXT)
+		nr_softirq_chains++;
+	else
+		nr_process_chains++;
+}
+
+static void dec_chains(int irq_context)
+{
+	if (irq_context & LOCK_CHAIN_HARDIRQ_CONTEXT)
+		nr_hardirq_chains--;
+	else if (irq_context & LOCK_CHAIN_SOFTIRQ_CONTEXT)
+		nr_softirq_chains--;
+	else
+		nr_process_chains--;
 }
 
 #else
@@ -2325,6 +2333,10 @@ static inline void inc_chains(void)
 	nr_process_chains++;
 }
 
+static void dec_chains(int irq_context)
+{
+	nr_process_chains--;
+}
 #endif /* CONFIG_TRACE_IRQFLAGS */
 
 static void
@@ -3037,7 +3049,7 @@ static inline int add_chain_cache(struct task_struct *curr,
 	chain_hlocks[chain->base + j] = class - lock_classes;
 	hlist_add_head_rcu(&chain->entry, hash_head);
 	debug_atomic_inc(chain_lookup_misses);
-	inc_chains();
+	inc_chains(chain->irq_context);
 
 	return 1;
 }
@@ -3790,7 +3802,8 @@ mark_usage(struct task_struct *curr, struct held_lock *hlock, int check)
 
 static inline unsigned int task_irq_context(struct task_struct *task)
 {
-	return 2 * !!task->hardirq_context + !!task->softirq_context;
+	return LOCK_CHAIN_HARDIRQ_CONTEXT * !!task->hardirq_context +
+	       LOCK_CHAIN_SOFTIRQ_CONTEXT * !!task->softirq_context;
 }
 
 static int separate_irq_context(struct task_struct *curr,
@@ -4980,6 +4993,8 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
 	free_chain_hlocks(chain->base, chain->depth);
 	/* Overwrite the chain key for concurrent RCU readers. */
 	WRITE_ONCE(chain->chain_key, INITIAL_CHAIN_KEY);
+	dec_chains(chain->irq_context);
+
 	/*
 	 * Note: calling hlist_del_rcu() from inside a
 	 * hlist_for_each_entry_rcu() loop is safe.
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 91bbc5684103..9425155b9053 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -98,6 +98,12 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
 
 #define MAX_LOCKDEP_CHAINS_BITS	16
 
+/*
+ * Bit definitions for lock_chain.irq_context
+ */
+#define LOCK_CHAIN_SOFTIRQ_CONTEXT	(1 << 0)
+#define LOCK_CHAIN_HARDIRQ_CONTEXT	(1 << 1)
+
 /*
  * Stack-trace: tightly packed array of stack backtrace
  * addresses. Protected by the hash_lock.
-- 
2.18.1