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Date: Sat, 14 Oct 2017 18:01:14 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: [GIT PULL] locking fixes
Message-ID: <20171014160114.pi72fsmqgys4hp3e@gmail.com>
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Linus,

Please pull the latest locking-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking-urgent-for-linus

   # HEAD: b483cf3bc249d7af706390efa63d6671e80d1c09 locking/lockdep: Disable cross-release features for now

Two lockdep fixes for bugs introduced by the cross-release dependency tracking 
feature - plus a commit that disables it because performance regressed in an 
absymal fashion on some systems.

 Thanks,

	Ingo

------------------>
Ingo Molnar (1):
      locking/lockdep: Disable cross-release features for now

Peter Zijlstra (2):
      locking/lockdep: Fix stacktrace mess
      locking/selftest: Avoid false BUG report


 kernel/locking/lockdep.c | 48 ++++++++++++++++++++----------------------------
 lib/Kconfig.debug        |  4 ++--
 lib/locking-selftest.c   |  2 ++
 3 files changed, 24 insertions(+), 30 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 44c8d0d17170..e36e652d996f 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1873,10 +1873,10 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	       struct held_lock *next, int distance, struct stack_trace *trace,
 	       int (*save)(struct stack_trace *trace))
 {
+	struct lock_list *uninitialized_var(target_entry);
 	struct lock_list *entry;
-	int ret;
 	struct lock_list this;
-	struct lock_list *uninitialized_var(target_entry);
+	int ret;
 
 	/*
 	 * Prove that the new <prev> -> <next> dependency would not
@@ -1890,8 +1890,17 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	this.class = hlock_class(next);
 	this.parent = NULL;
 	ret = check_noncircular(&this, hlock_class(prev), &target_entry);
-	if (unlikely(!ret))
+	if (unlikely(!ret)) {
+		if (!trace->entries) {
+			/*
+			 * If @save fails here, the printing might trigger
+			 * a WARN but because of the !nr_entries it should
+			 * not do bad things.
+			 */
+			save(trace);
+		}
 		return print_circular_bug(&this, target_entry, next, prev, trace);
+	}
 	else if (unlikely(ret < 0))
 		return print_bfs_bug(ret);
 
@@ -1938,7 +1947,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 		return print_bfs_bug(ret);
 
 
-	if (save && !save(trace))
+	if (!trace->entries && !save(trace))
 		return 0;
 
 	/*
@@ -1958,20 +1967,6 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	if (!ret)
 		return 0;
 
-	/*
-	 * Debugging printouts:
-	 */
-	if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) {
-		graph_unlock();
-		printk("\n new dependency: ");
-		print_lock_name(hlock_class(prev));
-		printk(KERN_CONT " => ");
-		print_lock_name(hlock_class(next));
-		printk(KERN_CONT "\n");
-		dump_stack();
-		if (!graph_lock())
-			return 0;
-	}
 	return 2;
 }
 
@@ -1986,8 +1981,12 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 {
 	int depth = curr->lockdep_depth;
 	struct held_lock *hlock;
-	struct stack_trace trace;
-	int (*save)(struct stack_trace *trace) = save_trace;
+	struct stack_trace trace = {
+		.nr_entries = 0,
+		.max_entries = 0,
+		.entries = NULL,
+		.skip = 0,
+	};
 
 	/*
 	 * Debugging checks.
@@ -2018,18 +2017,11 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 			 */
 			if (hlock->read != 2 && hlock->check) {
 				int ret = check_prev_add(curr, hlock, next,
-							 distance, &trace, save);
+							 distance, &trace, save_trace);
 				if (!ret)
 					return 0;
 
 				/*
-				 * Stop saving stack_trace if save_trace() was
-				 * called at least once:
-				 */
-				if (save && ret == 2)
-					save = NULL;
-
-				/*
 				 * Stop after the first non-trylock entry,
 				 * as non-trylock entries have added their
 				 * own direct dependencies already, so this
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2689b7c50c52..e2705843c524 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1092,8 +1092,8 @@ config PROVE_LOCKING
 	select DEBUG_MUTEXES
 	select DEBUG_RT_MUTEXES if RT_MUTEXES
 	select DEBUG_LOCK_ALLOC
-	select LOCKDEP_CROSSRELEASE
-	select LOCKDEP_COMPLETIONS
+	select LOCKDEP_CROSSRELEASE if BROKEN
+	select LOCKDEP_COMPLETIONS if BROKEN
 	select TRACE_IRQFLAGS
 	default n
 	help
diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index cd0b5c964bd0..2b827b8a1d8c 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -2031,11 +2031,13 @@ void locking_selftest(void)
 	print_testname("mixed read-lock/lock-write ABBA");
 	pr_cont("             |");
 	dotest(rlock_ABBA1, FAILURE, LOCKTYPE_RWLOCK);
+#ifdef CONFIG_PROVE_LOCKING
 	/*
 	 * Lockdep does indeed fail here, but there's nothing we can do about
 	 * that now.  Don't kill lockdep for it.
 	 */
 	unexpected_testcase_failures--;
+#endif
 
 	pr_cont("             |");
 	dotest(rwsem_ABBA1, FAILURE, LOCKTYPE_RWSEM);