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From:   Yuyang Du <duyuyang@gmail.com>
To:     peterz@infradead.org, will.deacon@arm.com, mingo@kernel.org
Cc:     bvanassche@acm.org, ming.lei@redhat.com, frederic@kernel.org,
        tglx@linutronix.de, linux-kernel@vger.kernel.org,
        longman@redhat.com, paulmck@linux.vnet.ibm.com,
        boqun.feng@gmail.com, Yuyang Du <duyuyang@gmail.com>
Subject: [PATCH v4 12/30] locking/lockdep: Specify the depth of current lock stack in lookup_chain_cache_add()
Date:   Thu, 29 Aug 2019 16:31:14 +0800
Message-Id: <20190829083132.22394-13-duyuyang@gmail.com>
In-Reply-To: <20190829083132.22394-1-duyuyang@gmail.com>
References: <20190829083132.22394-1-duyuyang@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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When looking up and adding a chain (i.e., in lookup_chain_cache_add() and
only in it), explicitly specify the depth of the held lock stack as the
chain. The depth now only equals curr->lockdep_depth.

No functional change.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
 kernel/locking/lockdep.c | 48 ++++++++++++++++++++++++++----------------------
 1 file changed, 26 insertions(+), 22 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 1dda9de..569d3c1 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2600,12 +2600,12 @@ struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
  * Returns the index of the first held_lock of the current chain
  */
 static inline int get_first_held_lock(struct task_struct *curr,
-					struct held_lock *hlock)
+				      struct held_lock *hlock, int depth)
 {
 	int i;
 	struct held_lock *hlock_curr;
 
-	for (i = curr->lockdep_depth - 1; i >= 0; i--) {
+	for (i = depth - 1; i >= 0; i--) {
 		hlock_curr = curr->held_locks + i;
 		if (hlock_curr->irq_context != hlock->irq_context)
 			break;
@@ -2630,12 +2630,12 @@ static u64 print_chain_key_iteration(int class_idx, u64 chain_key)
 }
 
 static void
-print_chain_keys_held_locks(struct task_struct *curr, struct held_lock *hlock_next)
+print_chain_keys_held_locks(struct task_struct *curr,
+			    struct held_lock *hlock_next, int depth)
 {
 	struct held_lock *hlock;
 	u64 chain_key = INITIAL_CHAIN_KEY;
-	int depth = curr->lockdep_depth;
-	int i = get_first_held_lock(curr, hlock_next);
+	int i = get_first_held_lock(curr, hlock_next, depth);
 
 	printk("depth: %u (irq_context %u)\n", depth - i + 1,
 		hlock_next->irq_context);
@@ -2667,8 +2667,8 @@ static void print_chain_keys_chain(struct lock_chain *chain)
 }
 
 static void print_collision(struct task_struct *curr,
-			struct held_lock *hlock_next,
-			struct lock_chain *chain)
+			    struct held_lock *hlock_next,
+			    struct lock_chain *chain, int depth)
 {
 	pr_warn("\n");
 	pr_warn("============================\n");
@@ -2679,7 +2679,7 @@ static void print_collision(struct task_struct *curr,
 	pr_warn("Hash chain already cached but the contents don't match!\n");
 
 	pr_warn("Held locks:");
-	print_chain_keys_held_locks(curr, hlock_next);
+	print_chain_keys_held_locks(curr, hlock_next, depth);
 
 	pr_warn("Locks in cached chain:");
 	print_chain_keys_chain(chain);
@@ -2695,17 +2695,16 @@ static void print_collision(struct task_struct *curr,
  * that there was a collision during the calculation of the chain_key.
  * Returns: 0 not passed, 1 passed
  */
-static int check_no_collision(struct task_struct *curr,
-			struct held_lock *hlock,
-			struct lock_chain *chain)
+static int check_no_collision(struct task_struct *curr, struct held_lock *hlock,
+			      struct lock_chain *chain, int depth)
 {
 #ifdef CONFIG_DEBUG_LOCKDEP
 	int i, j, id;
 
-	i = get_first_held_lock(curr, hlock);
+	i = get_first_held_lock(curr, hlock, depth);
 
-	if (DEBUG_LOCKS_WARN_ON(chain->depth != curr->lockdep_depth - (i - 1))) {
-		print_collision(curr, hlock, chain);
+	if (DEBUG_LOCKS_WARN_ON(chain->depth != depth - (i - 1))) {
+		print_collision(curr, hlock, chain, depth);
 		return 0;
 	}
 
@@ -2713,7 +2712,7 @@ static int check_no_collision(struct task_struct *curr,
 		id = curr->held_locks[i].class_idx;
 
 		if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) {
-			print_collision(curr, hlock, chain);
+			print_collision(curr, hlock, chain, depth);
 			return 0;
 		}
 	}
@@ -2757,7 +2756,7 @@ static struct lock_chain *alloc_lock_chain(void)
  */
 static inline struct lock_chain *add_chain_cache(struct task_struct *curr,
 						 struct held_lock *hlock,
-						 u64 chain_key)
+						 u64 chain_key, int depth)
 {
 	struct lock_class *class = hlock_class(hlock);
 	struct hlist_head *hash_head = chainhashentry(chain_key);
@@ -2783,8 +2782,8 @@ static inline struct lock_chain *add_chain_cache(struct task_struct *curr,
 	}
 	chain->chain_key = chain_key;
 	chain->irq_context = hlock->irq_context;
-	i = get_first_held_lock(curr, hlock);
-	chain->depth = curr->lockdep_depth + 1 - i;
+	i = get_first_held_lock(curr, hlock, depth);
+	chain->depth = depth + 1 - i;
 
 	BUILD_BUG_ON((1UL << 24) <= ARRAY_SIZE(chain_hlocks));
 	BUILD_BUG_ON((1UL << 6)  <= ARRAY_SIZE(curr->held_locks));
@@ -2837,17 +2836,21 @@ static inline struct lock_chain *lookup_chain_cache(u64 chain_key)
  * add it and return the chain - in this case the new dependency
  * chain will be validated. If the key is already hashed, return
  * NULL. (On return with the new chain graph_lock is held.)
+ *
+ * If the key is not hashed, the new chain is composed of @hlock
+ * and @depth worth of the current held lock stack, of which the
+ * held locks are in the same context as @hlock.
  */
 static inline struct lock_chain *
 lookup_chain_cache_add(struct task_struct *curr, struct held_lock *hlock,
-		       u64 chain_key)
+		       u64 chain_key, int depth)
 {
 	struct lock_class *class = hlock_class(hlock);
 	struct lock_chain *chain = lookup_chain_cache(chain_key);
 
 	if (chain) {
 cache_hit:
-		if (!check_no_collision(curr, hlock, chain))
+		if (!check_no_collision(curr, hlock, chain, depth))
 			return NULL;
 
 		if (very_verbose(class)) {
@@ -2877,7 +2880,7 @@ static inline struct lock_chain *lookup_chain_cache(u64 chain_key)
 		goto cache_hit;
 	}
 
-	return add_chain_cache(curr, hlock, chain_key);
+	return add_chain_cache(curr, hlock, chain_key, depth);
 }
 
 static int validate_chain(struct task_struct *curr, struct held_lock *hlock,
@@ -2895,7 +2898,8 @@ static int validate_chain(struct task_struct *curr, struct held_lock *hlock,
 	 * graph_lock for us)
 	 */
 	if (!hlock->trylock && hlock->check &&
-	    (chain = lookup_chain_cache_add(curr, hlock, chain_key))) {
+	    (chain = lookup_chain_cache_add(curr, hlock, chain_key,
+					    curr->lockdep_depth))) {
 		/*
 		 * Check whether last held lock:
 		 *
-- 
1.8.3.1