[PATCH AUTOSEL 4.9 45/45] locking/lockdep: Fix lock used or unused stats error

From: Sasha Levin
Date: Fri Jul 19 2019 - 00:17:29 EST

From: Yuyang Du <duyuyang@xxxxxxxxx>

[ Upstream commit 68d41d8c94a31dfb8233ab90b9baf41a2ed2da68 ]

The stats variable nr_unused_locks is incremented every time a new lock
class is register and decremented when the lock is first used in
__lock_acquire(). And after all, it is shown and checked in lockdep_stats.

However, under configurations that either CONFIG_TRACE_IRQFLAGS or
CONFIG_PROVE_LOCKING is not defined:

The commit:

091806515124b20 ("locking/lockdep: Consolidate lock usage bit initialization")

missed marking the LOCK_USED flag at IRQ usage initialization because
as mark_usage() is not called. And the commit:

886532aee3cd42d ("locking/lockdep: Move mark_lock() inside CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING")

further made mark_lock() not defined such that the LOCK_USED cannot be
marked at all when the lock is first acquired.

As a result, we fix this by not showing and checking the stats under such
configurations for lockdep_stats.

Reported-by: Qian Cai <cai@xxxxxx>
Signed-off-by: Yuyang Du <duyuyang@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: arnd@xxxxxxxx
Cc: frederic@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20190709101522.9117-1-duyuyang@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
kernel/locking/lockdep_proc.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index a0f61effad25..c482de6f5262 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -229,6 +229,7 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
nr_hardirq_read_safe = 0, nr_hardirq_read_unsafe = 0,
sum_forward_deps = 0;

list_for_each_entry(class, &all_lock_classes, lock_entry) {

if (class->usage_mask == 0)
@@ -260,12 +261,12 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
if (class->usage_mask & LOCKF_ENABLED_HARDIRQ_READ)

sum_forward_deps += lockdep_count_forward_deps(class);
DEBUG_LOCKS_WARN_ON(debug_atomic_read(nr_unused_locks) != nr_unused);
seq_printf(m, " lock-classes: %11lu [max: %lu]\n",
nr_lock_classes, MAX_LOCKDEP_KEYS);