[PATCH v3 05/14] locking/mutex: Add p->blocked_on wrappers

John Stultz
2023-04-11T04:25:54Z

From: Valentin Schneider <valentin.schneider@arm.com>

This lets us assert p->blocked_lock is held whenever we access
p->blocked_on.

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>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
[fix conflicts, call in more places]
Signed-off-by: Connor O'Brien <connoro@google.com>
[jstultz: tweaked commit subject, added get_task_blocked_on() as well]
Signed-off-by: John Stultz <jstultz@google.com>
---
v2:
* Added get_task_blocked_on() accessor
---
include/linux/sched.h | 14 ++++++++++++++
kernel/locking/mutex-debug.c | 4 ++--
kernel/locking/mutex.c | 8 ++++----
3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2d736b6c44e9..9d46ca8ac221 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2222,6 +2222,20 @@ static inline int rwlock_needbreak(rwlock_t *lock)
#endif
}

+static inline void set_task_blocked_on(struct task_struct *p, struct mutex *m)
+{
+ lockdep_assert_held(&p->blocked_lock);
+
+ p->blocked_on = m;
+}
+
+static inline struct mutex *get_task_blocked_on(struct task_struct *p)
+{
+ lockdep_assert_held(&p->blocked_lock);
+
+ return p->blocked_on;
+}
+
static __always_inline bool need_resched(void)
{
return unlikely(tif_need_resched());
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index 7228909c3e62..e3cd64ae6ea4 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -53,13 +53,13 @@ void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
lockdep_assert_held(&lock->wait_lock);

/* Current thread can't be already blocked (since it's executing!) */
- DEBUG_LOCKS_WARN_ON(task->blocked_on);
+ DEBUG_LOCKS_WARN_ON(get_task_blocked_on(task));
}

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);
+ struct mutex *blocked_on = get_task_blocked_on(task); /*XXX jstultz: dropped READ_ONCE here, revisit.*/

DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
DEBUG_LOCKS_WARN_ON(waiter->task != task);
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 9cb2686fb974..45f1b7519f63 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -647,7 +647,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
goto err_early_kill;
}

- current->blocked_on = lock;
+ set_task_blocked_on(current, lock);
set_current_state(state);
trace_contention_begin(lock, LCB_F_MUTEX);
for (;;) {
@@ -691,7 +691,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
/*
* Gets reset by ttwu_runnable().
*/
- current->blocked_on = lock;
+ set_task_blocked_on(current, lock);
set_current_state(state);
/*
* Here we order against unlock; we must either see it change
@@ -742,7 +742,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
debug_mutex_free_waiter(&waiter);

skip_wait:
- current->blocked_on = NULL;
+ set_task_blocked_on(current, NULL);
/* got the lock - cleanup and rejoice! */
lock_acquired(&lock->dep_map, ip);
trace_contention_end(lock, 0);
@@ -758,7 +758,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
return 0;

err:
- current->blocked_on = NULL;
+ set_task_blocked_on(current, NULL);
__set_current_state(TASK_RUNNING);
__mutex_remove_waiter(lock, &waiter);
err_early_kill:
--
2.40.0.577.gac1e443424-goog