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Subject[PATCH v5 1/7] locking/lockdep: Decrement irq context counters when removing lock chain
Date
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.

Since inc_chains() no longer accesses hardirq_context and softirq_context
directly, it is moved out from the CONFIG_TRACE_IRQFLAGS conditional
compilation block.

Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use")
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/lockdep.c | 40 +++++++++++++++++-------------
kernel/locking/lockdep_internals.h | 6 +++++
2 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 32406ef0d6a2..35449f5b79fb 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2298,18 +2298,6 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
return 0;
}

-static void inc_chains(void)
-{
- if (current->hardirq_context)
- nr_hardirq_chains++;
- else {
- if (current->softirq_context)
- nr_softirq_chains++;
- else
- nr_process_chains++;
- }
-}
-
#else

static inline int check_irq_usage(struct task_struct *curr,
@@ -2317,13 +2305,27 @@ static inline int check_irq_usage(struct task_struct *curr,
{
return 1;
}
+#endif /* CONFIG_TRACE_IRQFLAGS */

-static inline void inc_chains(void)
+static void inc_chains(int irq_context)
{
- nr_process_chains++;
+ 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++;
}

-#endif /* CONFIG_TRACE_IRQFLAGS */
+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--;
+}

static void
print_deadlock_scenario(struct held_lock *nxt, struct held_lock *prv)
@@ -2843,7 +2845,7 @@ static inline int add_chain_cache(struct task_struct *curr,

hlist_add_head_rcu(&chain->entry, hash_head);
debug_atomic_inc(chain_lookup_misses);
- inc_chains();
+ inc_chains(chain->irq_context);

return 1;
}
@@ -3596,7 +3598,8 @@ 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,
@@ -4798,6 +4801,8 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
return;
/* Overwrite the chain key for concurrent RCU readers. */
WRITE_ONCE(chain->chain_key, chain_key);
+ dec_chains(chain->irq_context);
+
/*
* Note: calling hlist_del_rcu() from inside a
* hlist_for_each_entry_rcu() loop is safe.
@@ -4819,6 +4824,7 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
}
*new_chain = *chain;
hlist_add_head_rcu(&new_chain->entry, chainhashentry(chain_key));
+ inc_chains(new_chain->irq_context);
#endif
}

diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 18d85aebbb57..a525368b8cf6 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -106,6 +106,12 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
#define STACK_TRACE_HASH_SIZE 16384
#endif

+/*
+ * Bit definitions for lock_chain.irq_context
+ */
+#define LOCK_CHAIN_SOFTIRQ_CONTEXT (1 << 0)
+#define LOCK_CHAIN_HARDIRQ_CONTEXT (1 << 1)
+
#define MAX_LOCKDEP_CHAINS (1UL << MAX_LOCKDEP_CHAINS_BITS)

#define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5)
--
2.18.1
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