add_chain_cache() can only be used by current context since it
depends on a task's held_locks which is not protected by lock.
However, it would be useful if a dependency chain can be built
in any context. This patch makes the chain building not depend
on its context.
Especially, crossrelease feature wants to do this. Crossrelease
feature introduces a additional dependency chain consisting of 2
lock classes using 2 hlock instances, to connect dependency
between different contexts.
Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
---
kernel/locking/lockdep.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 57 insertions(+)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index efd001c..4d51208 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2010,6 +2010,63 @@ struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
return lock_classes + chain_hlocks[chain->base + i];
}
+/*
+ * This can make it possible to build a chain between just two
+ * specified hlocks rather than between already held locks of
+ * the current task and newly held lock, which can be done by
+ * add_chain_cache().
+ *
+ * add_chain_cache() must be done within the lock owner's context,
+ * however this can be called in any context if two racy-less hlock
+ * instances were already taken by caller. Thus this can be useful
+ * when building a chain between two hlocks regardless of context.
+ */
+static inline int add_chain_cache_2hlocks(struct held_lock *prev,
+ struct held_lock *next,
+ u64 chain_key)
+{
+ struct hlist_head *hash_head = chainhashentry(chain_key);
+ struct lock_chain *chain;
+
+ /*
+ * Allocate a new chain entry from the static array, and add
+ * it to the hash:
+ */
+
+ /*
+ * We might need to take the graph lock, ensure we've got IRQs
+ * disabled to make this an IRQ-safe lock.. for recursion reasons
+ * lockdep won't complain about its own locking errors.
+ */
+ if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
+ return 0;
+
+ if (unlikely(nr_lock_chains >= MAX_LOCKDEP_CHAINS)) {
+ if (!debug_locks_off_graph_unlock())
+ return 0;
+
+ print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!");
+ dump_stack();
+ return 0;
+ }
+
+ chain = lock_chains + nr_lock_chains++;
+ chain->chain_key = chain_key;
+ chain->irq_context = next->irq_context;
+ chain->depth = 2;
+ if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
+ chain->base = nr_chain_hlocks;
+ nr_chain_hlocks += chain->depth;
+ chain_hlocks[chain->base] = prev->class_idx - 1;
+ chain_hlocks[chain->base + 1] = next->class_idx -1;
+ }
+ hlist_add_head_rcu(&chain->entry, hash_head);
+ debug_atomic_inc(chain_lookup_misses);
+ inc_chains();
+
+ return 1;
+}
+
static inline int add_chain_cache(struct task_struct *curr,
struct held_lock *hlock,
u64 chain_key)
--
1.9.1
--
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