[PATCH 3/3] lockdep: new annotation lock_downgrade()

J. R. Okajima
2017-02-02T16:45:20Z

The commit
f831948 2016-11-30 locking/lockdep: Provide a type check for lock_is_held
didn't fully support rwsem. Here downgrade_write() supports the added type.

Originally-written-by: Peter Zijlstra <peterz@infradead.org>
See-also: http://marc.info/?l=linux-kernel&m=148581164003149&w=2
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
---
include/linux/lockdep.h | 2 ++
kernel/locking/lockdep.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++
kernel/locking/rwsem.c | 6 ++----
3 files changed, 59 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 0345cbf..22f304c 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -361,6 +361,8 @@ static inline void lock_set_subclass(struct lockdep_map *lock,
lock_set_class(lock, lock->name, lock->key, subclass, ip);
}

+extern void lock_downgrade(struct lockdep_map *lock, unsigned long ip);
+
extern void lockdep_set_current_reclaim_state(gfp_t gfp_mask);
extern void lockdep_clear_current_reclaim_state(void);
extern void lockdep_trace_alloc(gfp_t mask);
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7dc8f8e..6a4a740 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3523,6 +3523,44 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
return 1;
}

+static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
+{
+ struct task_struct *curr = current;
+ struct held_lock *hlock;
+ unsigned int depth;
+ int i;
+
+ depth = curr->lockdep_depth;
+ /*
+ * This function is about (re)setting the class of a held lock,
+ * yet we're not actually holding any locks. Naughty user!
+ */
+ if (DEBUG_LOCKS_WARN_ON(!depth))
+ return 0;
+
+ hlock = find_held_lock(curr, lock, depth, &i);
+ if (!hlock)
+ return print_unlock_imbalance_bug(curr, lock, ip);
+
+ curr->lockdep_depth = i;
+ curr->curr_chain_key = hlock->prev_chain_key;
+
+ WARN(hlock->read, "downgrading a read lock");
+ hlock->read = 1;
+ hlock->acquire_ip = ip;
+
+ if (validate_held_lock(curr, depth, i))
+ return 0;
+
+ /*
+ * I took it apart and put it back together again, except now I have
+ * these 'spare' parts.. where shall I put them.
+ */
+ if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
+ return 0;
+ return 1;
+}
+
/*
* Remove the lock to the list of currently held locks - this gets
* called on mutex_unlock()/spin_unlock*() (or on a failed
@@ -3749,6 +3787,23 @@ void lock_set_class(struct lockdep_map *lock, const char *name,
}
EXPORT_SYMBOL_GPL(lock_set_class);

+void lock_downgrade(struct lockdep_map *lock, unsigned long ip)
+{
+ unsigned long flags;
+
+ if (unlikely(current->lockdep_recursion))
+ return;
+
+ raw_local_irq_save(flags);
+ current->lockdep_recursion = 1;
+ check_flags(flags);
+ if (__lock_downgrade(lock, ip))
+ check_chain_key(current);
+ current->lockdep_recursion = 0;
+ raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lock_downgrade);
+
/*
* We are not always called with irqs disabled - do that here,
* and also avoid lockdep recursion:
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 45ba475..31db3ef 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -123,10 +123,8 @@ EXPORT_SYMBOL(up_write);
*/
void downgrade_write(struct rw_semaphore *sem)
{
- /*
- * lockdep: a downgraded write will live on as a write
- * dependency.
- */
+ lock_downgrade(&sem->dep_map, _RET_IP_);
+
rwsem_set_reader_owned(sem);
__downgrade_write(sem);
}
--
2.1.4