linux-kernel - [PATCH v3 07/30] locking/lockdep: Remove indirect dependency redundancy check

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Date:   Fri, 28 Jun 2019 17:15:05 +0800
From:   Yuyang Du <duyuyang@...il.com>
To:     peterz@...radead.org, will.deacon@....com, mingo@...nel.org
Cc:     bvanassche@....org, ming.lei@...hat.com, frederic@...nel.org,
        tglx@...utronix.de, linux-kernel@...r.kernel.org,
        longman@...hat.com, paulmck@...ux.vnet.ibm.com,
        boqun.feng@...il.com, Yuyang Du <duyuyang@...il.com>
Subject: [PATCH v3 07/30] locking/lockdep: Remove indirect dependency redundancy check

Indirect dependency redundancy check was added for cross-release, which
has been reverted. Then suggested by Peter, only when setting
CONFIG_LOCKDEP_SMALL it takes effect.

With (recursive) read-write lock types considered in dependency graph,
indirect dependency redundancy check would be very complicated if not
impossible to be correctly done. Lets remove it for good.

Signed-off-by: Yuyang Du <duyuyang@...il.com>
---
 kernel/locking/lockdep.c           | 41 --------------------------------------
 kernel/locking/lockdep_internals.h |  1 -
 kernel/locking/lockdep_proc.c      |  2 --
 3 files changed, 44 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index f171c6e..c61fdef 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1744,38 +1744,6 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
 	return ret;
 }
 
-#ifdef CONFIG_LOCKDEP_SMALL
-/*
- * Check that the dependency graph starting at <src> can lead to
- * <target> or not. If it can, <src> -> <target> dependency is already
- * in the graph.
- *
- * Print an error and return 2 if it does or 1 if it does not.
- */
-static noinline int
-check_redundant(struct held_lock *src, struct held_lock *target)
-{
-	int ret;
-	struct lock_list *uninitialized_var(target_entry);
-	struct lock_list src_entry = {
-		.class = hlock_class(src),
-		.parent = NULL,
-	};
-
-	debug_atomic_inc(nr_redundant_checks);
-
-	ret = check_path(hlock_class(target), &src_entry, &target_entry);
-
-	if (!ret) {
-		debug_atomic_inc(nr_redundant);
-		ret = 2;
-	} else if (ret < 0)
-		ret = 0;
-
-	return ret;
-}
-#endif
-
 #ifdef CONFIG_TRACE_IRQFLAGS
 
 static inline int usage_accumulate(struct lock_list *entry, void *mask)
@@ -2437,15 +2405,6 @@ static inline void inc_chains(void)
 		}
 	}
 
-#ifdef CONFIG_LOCKDEP_SMALL
-	/*
-	 * Is the <prev> -> <next> link redundant?
-	 */
-	ret = check_redundant(prev, next);
-	if (ret != 1)
-		return ret;
-#endif
-
 	if (!trace->nr_entries && !save_trace(trace))
 		return 0;
 
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index cc83568..e9a8ed6 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -170,7 +170,6 @@ struct lockdep_stats {
 	unsigned long  redundant_softirqs_on;
 	unsigned long  redundant_softirqs_off;
 	int            nr_unused_locks;
-	unsigned int   nr_redundant_checks;
 	unsigned int   nr_redundant;
 	unsigned int   nr_cyclic_checks;
 	unsigned int   nr_find_usage_forwards_checks;
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 9c49ec6..58ed889 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -178,8 +178,6 @@ static void lockdep_stats_debug_show(struct seq_file *m)
 		debug_atomic_read(chain_lookup_hits));
 	seq_printf(m, " cyclic checks:                 %11llu\n",
 		debug_atomic_read(nr_cyclic_checks));
-	seq_printf(m, " redundant checks:              %11llu\n",
-		debug_atomic_read(nr_redundant_checks));
 	seq_printf(m, " redundant links:               %11llu\n",
 		debug_atomic_read(nr_redundant));
 	seq_printf(m, " find-mask forwards checks:     %11llu\n",
-- 
1.8.3.1