[PATCH v2 2/6] locking/lockdep: Throw away all lock chains with zapped class

Waiman Long
2019-12-16T15:16:06Z

If a lock chain contains a class that is zapped, the whole lock chain is
now invalid. There is no point in keeping a partial chain behind hoping
it can be useful. So just dump the corresponding chain_hlocks entries for
now. A latter patch will try to reuse the freed chain_hlocks entries.

This patch also changes the type of nr_chain_hlocks to unsigned integer
to be consistent with the other counters.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/lockdep.c | 36 ++++--------------------------
kernel/locking/lockdep_internals.h | 4 ++--
kernel/locking/lockdep_proc.c | 2 +-
3 files changed, 7 insertions(+), 35 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c8d0374101b0..30ebfe4978d5 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2624,8 +2624,8 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)

struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
static DECLARE_BITMAP(lock_chains_in_use, MAX_LOCKDEP_CHAINS);
-int nr_chain_hlocks;
static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
+unsigned int nr_chain_hlocks;

struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
{
@@ -4770,57 +4770,29 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
struct lock_class *class)
{
#ifdef CONFIG_PROVE_LOCKING
- struct lock_chain *new_chain;
- u64 chain_key;
int i;

for (i = chain->base; i < chain->base + chain->depth; i++) {
if (chain_hlocks[i] != class - lock_classes)
continue;
- /* The code below leaks one chain_hlock[] entry. */
- if (--chain->depth > 0) {
- memmove(&chain_hlocks[i], &chain_hlocks[i + 1],
- (chain->base + chain->depth - i) *
- sizeof(chain_hlocks[0]));
- }
/*
* Each lock class occurs at most once in a lock chain so once
* we found a match we can break out of this loop.
*/
- goto recalc;
+ goto free_lock_chain;
}
/* Since the chain has not been modified, return. */
return;

-recalc:
- chain_key = INITIAL_CHAIN_KEY;
- for (i = chain->base; i < chain->base + chain->depth; i++)
- chain_key = iterate_chain_key(chain_key, chain_hlocks[i]);
- if (chain->depth && chain->chain_key == chain_key)
- return;
+free_lock_chain:
/* Overwrite the chain key for concurrent RCU readers. */
- WRITE_ONCE(chain->chain_key, chain_key);
+ WRITE_ONCE(chain->chain_key, INITIAL_CHAIN_KEY);
/*
* Note: calling hlist_del_rcu() from inside a
* hlist_for_each_entry_rcu() loop is safe.
*/
hlist_del_rcu(&chain->entry);
__set_bit(chain - lock_chains, pf->lock_chains_being_freed);
- if (chain->depth == 0)
- return;
- /*
- * If the modified lock chain matches an existing lock chain, drop
- * the modified lock chain.
- */
- if (lookup_chain_cache(chain_key))
- return;
- new_chain = alloc_lock_chain();
- if (WARN_ON_ONCE(!new_chain)) {
- debug_locks_off();
- return;
- }
- *new_chain = *chain;
- hlist_add_head_rcu(&new_chain->entry, chainhashentry(chain_key));
#endif
}

diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index a31d16fd3c43..5dec0fe12507 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -128,14 +128,14 @@ extern unsigned long nr_zapped_classes;
extern unsigned long nr_list_entries;
long lockdep_next_lockchain(long i);
unsigned long lock_chain_count(void);
-extern int nr_chain_hlocks;
extern unsigned long nr_stack_trace_entries;

extern unsigned int nr_hardirq_chains;
extern unsigned int nr_softirq_chains;
extern unsigned int nr_process_chains;
-extern unsigned int max_lockdep_depth;
+extern unsigned int nr_chain_hlocks;

+extern unsigned int max_lockdep_depth;
extern unsigned int max_bfs_queue_depth;

#ifdef CONFIG_PROVE_LOCKING
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index d98d349bb648..4c7dc0a8935d 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -271,7 +271,7 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
#ifdef CONFIG_PROVE_LOCKING
seq_printf(m, " dependency chains: %11lu [max: %lu]\n",
lock_chain_count(), MAX_LOCKDEP_CHAINS);
- seq_printf(m, " dependency chain hlocks: %11d [max: %lu]\n",
+ seq_printf(m, " dependency chain hlocks: %11u [max: %lu]\n",
nr_chain_hlocks, MAX_LOCKDEP_CHAIN_HLOCKS);
#endif

--
2.18.1