Merge tag 'locking-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar:

 - Core locking & atomics:

     - Convert all architectures to ARCH_ATOMIC: move every architecture
       to ARCH_ATOMIC, then get rid of ARCH_ATOMIC and all the
       transitory facilities and #ifdefs.

       Much reduction in complexity from that series:

           63 files changed, 756 insertions(+), 4094 deletions(-)

     - Self-test enhancements

 - Futexes:

     - Add the new FUTEX_LOCK_PI2 ABI, which is a variant that doesn't
       set FLAGS_CLOCKRT (.e. uses CLOCK_MONOTONIC).

       [ The temptation to repurpose FUTEX_LOCK_PI's implicit setting of
         FLAGS_CLOCKRT & invert the flag's meaning to avoid having to
         introduce a new variant was resisted successfully. ]

     - Enhance futex self-tests

 - Lockdep:

     - Fix dependency path printouts

     - Optimize trace saving

     - Broaden & fix wait-context checks

 - Misc cleanups and fixes.

* tag 'locking-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (52 commits)
  locking/lockdep: Correct the description error for check_redundant()
  futex: Provide FUTEX_LOCK_PI2 to support clock selection
  futex: Prepare futex_lock_pi() for runtime clock selection
  lockdep/selftest: Remove wait-type RCU_CALLBACK tests
  lockdep/selftests: Fix selftests vs PROVE_RAW_LOCK_NESTING
  lockdep: Fix wait-type for empty stack
  locking/selftests: Add a selftest for check_irq_usage()
  lockding/lockdep: Avoid to find wrong lock dep path in check_irq_usage()
  locking/lockdep: Remove the unnecessary trace saving
  locking/lockdep: Fix the dep path printing for backwards BFS
  selftests: futex: Add futex compare requeue test
  selftests: futex: Add futex wait test
  seqlock: Remove trailing semicolon in macros
  locking/lockdep: Reduce LOCKDEP dependency list
  locking/lockdep,doc: Improve readability of the block matrix
  locking/atomics: atomic-instrumented: simplify ifdeffery
  locking/atomic: delete !ARCH_ATOMIC remnants
  locking/atomic: xtensa: move to ARCH_ATOMIC
  locking/atomic: sparc: move to ARCH_ATOMIC
  locking/atomic: sh: move to ARCH_ATOMIC
  ...

1 files changed, 119 insertions, 8 deletions

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e32313072506..0c0524bfff99 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2306,7 +2306,56 @@ static void print_lock_class_header(struct lock_class *class, int depth)
 }
 
 /*
- * printk the shortest lock dependencies from @start to @end in reverse order:
+ * Dependency path printing:
+ *
+ * After BFS we get a lock dependency path (linked via ->parent of lock_list),
+ * printing out each lock in the dependency path will help on understanding how
+ * the deadlock could happen. Here are some details about dependency path
+ * printing:
+ *
+ * 1)	A lock_list can be either forwards or backwards for a lock dependency,
+ * 	for a lock dependency A -> B, there are two lock_lists:
+ *
+ * 	a)	lock_list in the ->locks_after list of A, whose ->class is B and
+ * 		->links_to is A. In this case, we can say the lock_list is
+ * 		"A -> B" (forwards case).
+ *
+ * 	b)	lock_list in the ->locks_before list of B, whose ->class is A
+ * 		and ->links_to is B. In this case, we can say the lock_list is
+ * 		"B <- A" (bacwards case).
+ *
+ * 	The ->trace of both a) and b) point to the call trace where B was
+ * 	acquired with A held.
+ *
+ * 2)	A "helper" lock_list is introduced during BFS, this lock_list doesn't
+ * 	represent a certain lock dependency, it only provides an initial entry
+ * 	for BFS. For example, BFS may introduce a "helper" lock_list whose
+ * 	->class is A, as a result BFS will search all dependencies starting with
+ * 	A, e.g. A -> B or A -> C.
+ *
+ * 	The notation of a forwards helper lock_list is like "-> A", which means
+ * 	we should search the forwards dependencies starting with "A", e.g A -> B
+ * 	or A -> C.
+ *
+ * 	The notation of a bacwards helper lock_list is like "<- B", which means
+ * 	we should search the backwards dependencies ending with "B", e.g.
+ * 	B <- A or B <- C.
+ */
+
+/*
+ * printk the shortest lock dependencies from @root to @leaf in reverse order.
+ *
+ * We have a lock dependency path as follow:
+ *
+ *    @root                                                                 @leaf
+ *      |                                                                     |
+ *      V                                                                     V
+ *	          ->parent                                   ->parent
+ * | lock_list | <--------- | lock_list | ... | lock_list  | <--------- | lock_list |
+ * |    -> L1  |            | L1 -> L2  | ... |Ln-2 -> Ln-1|            | Ln-1 -> Ln|
+ *
+ * , so it's natural that we start from @leaf and print every ->class and
+ * ->trace until we reach the @root.
  */
 static void __used
 print_shortest_lock_dependencies(struct lock_list *leaf,
@@ -2334,6 +2383,61 @@ print_shortest_lock_dependencies(struct lock_list *leaf,
 	} while (entry && (depth >= 0));
 }
 
+/*
+ * printk the shortest lock dependencies from @leaf to @root.
+ *
+ * We have a lock dependency path (from a backwards search) as follow:
+ *
+ *    @leaf                                                                 @root
+ *      |                                                                     |
+ *      V                                                                     V
+ *	          ->parent                                   ->parent
+ * | lock_list | ---------> | lock_list | ... | lock_list  | ---------> | lock_list |
+ * | L2 <- L1  |            | L3 <- L2  | ... | Ln <- Ln-1 |            |    <- Ln  |
+ *
+ * , so when we iterate from @leaf to @root, we actually print the lock
+ * dependency path L1 -> L2 -> .. -> Ln in the non-reverse order.
+ *
+ * Another thing to notice here is that ->class of L2 <- L1 is L1, while the
+ * ->trace of L2 <- L1 is the call trace of L2, in fact we don't have the call
+ * trace of L1 in the dependency path, which is alright, because most of the
+ * time we can figure out where L1 is held from the call trace of L2.
+ */
+static void __used
+print_shortest_lock_dependencies_backwards(struct lock_list *leaf,
+					   struct lock_list *root)
+{
+	struct lock_list *entry = leaf;
+	const struct lock_trace *trace = NULL;
+	int depth;
+
+	/*compute depth from generated tree by BFS*/
+	depth = get_lock_depth(leaf);
+
+	do {
+		print_lock_class_header(entry->class, depth);
+		if (trace) {
+			printk("%*s ... acquired at:\n", depth, "");
+			print_lock_trace(trace, 2);
+			printk("\n");
+		}
+
+		/*
+		 * Record the pointer to the trace for the next lock_list
+		 * entry, see the comments for the function.
+		 */
+		trace = entry->trace;
+
+		if (depth == 0 && (entry != root)) {
+			printk("lockdep:%s bad path found in chain graph\n", __func__);
+			break;
+		}
+
+		entry = get_lock_parent(entry);
+		depth--;
+	} while (entry && (depth >= 0));
+}
+
 static void
 print_irq_lock_scenario(struct lock_list *safe_entry,
 			struct lock_list *unsafe_entry,
@@ -2448,10 +2552,7 @@ print_bad_irq_dependency(struct task_struct *curr,
 	lockdep_print_held_locks(curr);
 
 	pr_warn("\nthe dependencies between %s-irq-safe lock and the holding lock:\n", irqclass);
-	prev_root->trace = save_trace();
-	if (!prev_root->trace)
-		return;
-	print_shortest_lock_dependencies(backwards_entry, prev_root);
+	print_shortest_lock_dependencies_backwards(backwards_entry, prev_root);
 
 	pr_warn("\nthe dependencies between the lock to be acquired");
 	pr_warn(" and %s-irq-unsafe lock:\n", irqclass);
@@ -2669,8 +2770,18 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
 	 * Step 3: we found a bad match! Now retrieve a lock from the backward
 	 * list whose usage mask matches the exclusive usage mask from the
 	 * lock found on the forward list.
+	 *
+	 * Note, we should only keep the LOCKF_ENABLED_IRQ_ALL bits, considering
+	 * the follow case:
+	 *
+	 * When trying to add A -> B to the graph, we find that there is a
+	 * hardirq-safe L, that L -> ... -> A, and another hardirq-unsafe M,
+	 * that B -> ... -> M. However M is **softirq-safe**, if we use exact
+	 * invert bits of M's usage_mask, we will find another lock N that is
+	 * **softirq-unsafe** and N -> ... -> A, however N -> .. -> M will not
+	 * cause a inversion deadlock.
 	 */
-	backward_mask = original_mask(target_entry1->class->usage_mask);
+	backward_mask = original_mask(target_entry1->class->usage_mask & LOCKF_ENABLED_IRQ_ALL);
 
 	ret = find_usage_backwards(&this, backward_mask, &target_entry);
 	if (bfs_error(ret)) {
@@ -2720,7 +2831,7 @@ static inline bool usage_skip(struct lock_list *entry, void *mask)
  * <target> or not. If it can, <src> -> <target> dependency is already
  * in the graph.
  *
- * Return BFS_RMATCH if it does, or BFS_RMATCH if it does not, return BFS_E* if
+ * Return BFS_RMATCH if it does, or BFS_RNOMATCH if it does not, return BFS_E* if
  * any error appears in the bfs search.
  */
 static noinline enum bfs_result
@@ -4579,7 +4690,7 @@ static int check_wait_context(struct task_struct *curr, struct held_lock *next)
 	u8 curr_inner;
 	int depth;
 
-	if (!curr->lockdep_depth || !next_inner || next->trylock)
+	if (!next_inner || next->trylock)
 		return 0;
 
 	if (!next_outer)