[PATCH v2 02/12] locking/mutex: Rework task_struct::blocked_on

John Stultz
2023-03-20T23:37:47Z

From: Peter Zijlstra <peterz@infradead.org>

Track the blocked-on relation for mutexes, this allows following this
relation at schedule time.

task
| blocked-on
v
mutex
| owner
v
task

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: kernel-team@android.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[minor changes while rebasing]
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Connor O'Brien <connoro@google.com>
[jstultz: Fix blocked_on tracking in __mutex_lock_common in error paths]
Signed-off-by: John Stultz <jstultz@google.com>
---
v2:
* Fixed blocked_on tracking in error paths that was causing crashes
---
include/linux/sched.h | 6 ++----
kernel/fork.c | 4 ++--
kernel/locking/mutex-debug.c | 9 +++++----
kernel/locking/mutex.c | 7 +++++++
4 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 63d242164b1a..9924d1926bc3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1139,10 +1139,8 @@ struct task_struct {
struct rt_mutex_waiter *pi_blocked_on;
#endif

-#ifdef CONFIG_DEBUG_MUTEXES
- /* Mutex deadlock detection: */
- struct mutex_waiter *blocked_on;
-#endif
+ struct task_struct *blocked_proxy; /* task that is boosting us */
+ struct mutex *blocked_on; /* lock we're blocked on */

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
int non_block_count;
diff --git a/kernel/fork.c b/kernel/fork.c
index d8cda4c6de6c..ad27fa09fe70 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2223,9 +2223,9 @@ static __latent_entropy struct task_struct *copy_process(
lockdep_init_task(p);
#endif

-#ifdef CONFIG_DEBUG_MUTEXES
+ p->blocked_proxy = NULL; /* nobody is boosting us yet */
p->blocked_on = NULL; /* not blocked yet */
-#endif
+
#ifdef CONFIG_BCACHE
p->sequential_io = 0;
p->sequential_io_avg = 0;
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index bc8abb8549d2..7228909c3e62 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -52,17 +52,18 @@ void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
{
lockdep_assert_held(&lock->wait_lock);

- /* Mark the current thread as blocked on the lock: */
- task->blocked_on = waiter;
+ /* Current thread can't be already blocked (since it's executing!) */
+ DEBUG_LOCKS_WARN_ON(task->blocked_on);
}

void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
struct task_struct *task)
{
+ struct mutex *blocked_on = READ_ONCE(task->blocked_on);
+
DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
DEBUG_LOCKS_WARN_ON(waiter->task != task);
- DEBUG_LOCKS_WARN_ON(task->blocked_on != waiter);
- task->blocked_on = NULL;
+ DEBUG_LOCKS_WARN_ON(blocked_on && blocked_on != lock);

INIT_LIST_HEAD(&waiter->list);
waiter->task = NULL;
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 1582756914df..f5296aa82255 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -645,6 +645,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
goto err_early_kill;
}

+ current->blocked_on = lock;
set_current_state(state);
trace_contention_begin(lock, LCB_F_MUTEX);
for (;;) {
@@ -682,6 +683,10 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas

first = __mutex_waiter_is_first(lock, &waiter);

+ /*
+ * Gets reset by ttwu_runnable().
+ */
+ current->blocked_on = lock;
set_current_state(state);
/*
* Here we order against unlock; we must either see it change
@@ -719,6 +724,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
debug_mutex_free_waiter(&waiter);

skip_wait:
+ current->blocked_on = NULL;
/* got the lock - cleanup and rejoice! */
lock_acquired(&lock->dep_map, ip);
trace_contention_end(lock, 0);
@@ -733,6 +739,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
return 0;

err:
+ current->blocked_on = NULL;
__set_current_state(TASK_RUNNING);
__mutex_remove_waiter(lock, &waiter);
err_early_kill:
--
2.40.0.rc1.284.g88254d51c5-goog