lockdep: Take read/write status in consideration when generate chainkey

Currently, the chainkey of a lock chain is a hash sum of the class_idx
of all the held locks, the read/write status are not taken in to
consideration while generating the chainkey. This could result into a
problem, if we have:

	P1()
	{
		read_lock(B);
		lock(A);
	}

	P2()
	{
		lock(A);
		read_lock(B);
	}

	P3()
	{
		lock(A);
		write_lock(B);
	}

, and P1(), P2(), P3() run one by one. And when running P2(), lockdep
detects such a lock chain A -> B is not a deadlock, then it's added in
the chain cache, and then when running P3(), even if it's a deadlock, we
could miss it because of the hit of chain cache. This could be confirmed
by self testcase "chain cached mixed R-L/L-W ".

To resolve this, we use concept "hlock_id" to generate the chainkey, the
hlock_id is a tuple (hlock->class_idx, hlock->read), which fits in a u16
type. With this, the chainkeys are different is the lock sequences have
the same locks but different read/write status.

Besides, since we use "hlock_id" to generate chainkeys, the chain_hlocks
array now store the "hlock_id"s rather than lock_class indexes.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-15-boqun.feng@gmail.com

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index b87766e080f5df7deffcc5aff7ce585a9921a8eb..cccf4bc759c6131869288d8c12b37875ca8332a3 100644 (file)
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -371,6 +371,21 @@ static struct hlist_head classhash_table[CLASSHASH_SIZE];
 
 static struct hlist_head chainhash_table[CHAINHASH_SIZE];
 
+/*
+ * the id of held_lock
+ */
+static inline u16 hlock_id(struct held_lock *hlock)
+{
+       BUILD_BUG_ON(MAX_LOCKDEP_KEYS_BITS + 2 > 16);
+
+       return (hlock->class_idx | (hlock->read << MAX_LOCKDEP_KEYS_BITS));
+}
+
+static inline unsigned int chain_hlock_class_idx(u16 hlock_id)
+{
+       return hlock_id & (MAX_LOCKDEP_KEYS - 1);
+}
+
 /*
  * The hash key of the lock dependency chains is a hash itself too:
  * it's a hash of all locks taken up to that lock, including that lock.
@@ -3202,7 +3217,10 @@ static inline void free_chain_hlocks(int base, int size)
 
 struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
 {
-       return lock_classes + chain_hlocks[chain->base + i];
+       u16 chain_hlock = chain_hlocks[chain->base + i];
+       unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
+
+       return lock_classes + class_idx - 1;
 }
 
 /*
@@ -3228,12 +3246,12 @@ static inline int get_first_held_lock(struct task_struct *curr,
 /*
  * Returns the next chain_key iteration
  */
-static u64 print_chain_key_iteration(int class_idx, u64 chain_key)
+static u64 print_chain_key_iteration(u16 hlock_id, u64 chain_key)
 {
-       u64 new_chain_key = iterate_chain_key(chain_key, class_idx);
+       u64 new_chain_key = iterate_chain_key(chain_key, hlock_id);
 
-       printk(" class_idx:%d -> chain_key:%016Lx",
-               class_idx,
+       printk(" hlock_id:%d -> chain_key:%016Lx",
+               (unsigned int)hlock_id,
                (unsigned long long)new_chain_key);
        return new_chain_key;
 }
@@ -3250,12 +3268,12 @@ print_chain_keys_held_locks(struct task_struct *curr, struct held_lock *hlock_ne
                hlock_next->irq_context);
        for (; i < depth; i++) {
                hlock = curr->held_locks + i;
-               chain_key = print_chain_key_iteration(hlock->class_idx, chain_key);
+               chain_key = print_chain_key_iteration(hlock_id(hlock), chain_key);
 
                print_lock(hlock);
        }
 
-       print_chain_key_iteration(hlock_next->class_idx, chain_key);
+       print_chain_key_iteration(hlock_id(hlock_next), chain_key);
        print_lock(hlock_next);
 }
 
@@ -3263,14 +3281,14 @@ static void print_chain_keys_chain(struct lock_chain *chain)
 {
        int i;
        u64 chain_key = INITIAL_CHAIN_KEY;
-       int class_id;
+       u16 hlock_id;
 
        printk("depth: %u\n", chain->depth);
        for (i = 0; i < chain->depth; i++) {
-               class_id = chain_hlocks[chain->base + i];
-               chain_key = print_chain_key_iteration(class_id, chain_key);
+               hlock_id = chain_hlocks[chain->base + i];
+               chain_key = print_chain_key_iteration(hlock_id, chain_key);
 
-               print_lock_name(lock_classes + class_id);
+               print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id) - 1);
                printk("\n");
        }
 }
@@ -3319,7 +3337,7 @@ static int check_no_collision(struct task_struct *curr,
        }
 
        for (j = 0; j < chain->depth - 1; j++, i++) {
-               id = curr->held_locks[i].class_idx;
+               id = hlock_id(&curr->held_locks[i]);
 
                if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) {
                        print_collision(curr, hlock, chain);
@@ -3368,7 +3386,6 @@ static inline int add_chain_cache(struct task_struct *curr,
                                  struct held_lock *hlock,
                                  u64 chain_key)
 {
-       struct lock_class *class = hlock_class(hlock);
        struct hlist_head *hash_head = chainhashentry(chain_key);
        struct lock_chain *chain;
        int i, j;
@@ -3411,11 +3428,11 @@ static inline int add_chain_cache(struct task_struct *curr,
 
        chain->base = j;
        for (j = 0; j < chain->depth - 1; j++, i++) {
-               int lock_id = curr->held_locks[i].class_idx;
+               int lock_id = hlock_id(curr->held_locks + i);
 
                chain_hlocks[chain->base + j] = lock_id;
        }
-       chain_hlocks[chain->base + j] = class - lock_classes;
+       chain_hlocks[chain->base + j] = hlock_id(hlock);
        hlist_add_head_rcu(&chain->entry, hash_head);
        debug_atomic_inc(chain_lookup_misses);
        inc_chains(chain->irq_context);
@@ -3602,7 +3619,7 @@ static void check_chain_key(struct task_struct *curr)
                if (prev_hlock && (prev_hlock->irq_context !=
                                                        hlock->irq_context))
                        chain_key = INITIAL_CHAIN_KEY;
-               chain_key = iterate_chain_key(chain_key, hlock->class_idx);
+               chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
                prev_hlock = hlock;
        }
        if (chain_key != curr->curr_chain_key) {
@@ -4749,7 +4766,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
                chain_key = INITIAL_CHAIN_KEY;
                chain_head = 1;
        }
-       chain_key = iterate_chain_key(chain_key, class_idx);
+       chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
 
        if (nest_lock && !__lock_is_held(nest_lock, -1)) {
                print_lock_nested_lock_not_held(curr, hlock, ip);
@@ -5648,7 +5665,7 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
        int i;
 
        for (i = chain->base; i < chain->base + chain->depth; i++) {
-               if (chain_hlocks[i] != class - lock_classes)
+               if (chain_hlock_class_idx(chain_hlocks[i]) != class - lock_classes)
                        continue;
                /*
                 * Each lock class occurs at most once in a lock chain so once