[PATCH AUTOSEL 5.4 126/330] locking/lockdep: Decrement IRQ context counters when removing lock chain

Sasha Levin
2020-09-18T02:03:54Z

From: Waiman Long <longman@redhat.com>

[ Upstream commit b3b9c187dc2544923a601733a85352b9ddaba9b3 ]

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.
IRQ
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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200206152408.24165-2-longman@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 9ab1a965c3b92..bca0f7f71cde4 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2302,18 +2302,6 @@ 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,
@@ -2321,13 +2309,27 @@ 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)
@@ -2847,7 +2849,7 @@ 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;
}
@@ -3600,7 +3602,8 @@ lock_used:

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,
@@ -4805,6 +4808,8 @@ recalc:
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.
@@ -4826,6 +4831,7 @@ recalc:
}
*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 18d85aebbb57f..a525368b8cf61 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)
--
2.25.1