locking/lockdep: Fix merging of hlocks with non-zero references

BugLink: https://bugs.launchpad.net/bugs/1839036
[ Upstream commit d9349850e188b8b59e5322fda17ff389a1c0cd7d ]

The sequence

	static DEFINE_WW_CLASS(test_ww_class);

	struct ww_acquire_ctx ww_ctx;
	struct ww_mutex ww_lock_a;
	struct ww_mutex ww_lock_b;
	struct ww_mutex ww_lock_c;
	struct mutex lock_c;

	ww_acquire_init(&ww_ctx, &test_ww_class);

	ww_mutex_init(&ww_lock_a, &test_ww_class);
	ww_mutex_init(&ww_lock_b, &test_ww_class);
	ww_mutex_init(&ww_lock_c, &test_ww_class);

	mutex_init(&lock_c);

	ww_mutex_lock(&ww_lock_a, &ww_ctx);

	mutex_lock(&lock_c);

	ww_mutex_lock(&ww_lock_b, &ww_ctx);
	ww_mutex_lock(&ww_lock_c, &ww_ctx);

	mutex_unlock(&lock_c);	(*)

	ww_mutex_unlock(&ww_lock_c);
	ww_mutex_unlock(&ww_lock_b);
	ww_mutex_unlock(&ww_lock_a);

	ww_acquire_fini(&ww_ctx); (**)

will trigger the following error in __lock_release() when calling
mutex_release() at **:

	DEBUG_LOCKS_WARN_ON(depth <= 0)

The problem is that the hlock merging happening at * updates the
references for test_ww_class incorrectly to 3 whereas it should've
updated it to 4 (representing all the instances for ww_ctx and
ww_lock_[abc]).

Fix this by updating the references during merging correctly taking into
account that we can have non-zero references (both for the hlock that we
merge into another hlock or for the hlock we are merging into).

Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190524201509.9199-2-imre.deak@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 54e675695d7e80393c746b04085880af5656c308..76d85d605121144a15ef5f5ff6e083efc7bd5791 100644 (file)
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3344,17 +3344,17 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
        if (depth) {
                hlock = curr->held_locks + depth - 1;
                if (hlock->class_idx == class_idx && nest_lock) {
-                       if (hlock->references) {
-                               /*
-                                * Check: unsigned int references:12, overflow.
-                                */
-                               if (DEBUG_LOCKS_WARN_ON(hlock->references == (1 << 12)-1))
-                                       return 0;
+                       if (!references)
+                               references++;
 
+                       if (!hlock->references)
                                hlock->references++;
-                       } else {
-                               hlock->references = 2;
-                       }
+
+                       hlock->references += references;
+
+                       /* Overflow */
+                       if (DEBUG_LOCKS_WARN_ON(hlock->references < references))
+                               return 0;
 
                        return 1;
                }