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    Subject[RFC PATCH 03/11] kernel/locking: Add p->blocked_on wrapper
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    From: Valentin Schneider <valentin.schneider@arm.com>

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

    XXX: just make a pointer return, so we can also check at get's.

    Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
    [fix conflicts]
    Signed-off-by: Connor O'Brien <connoro@google.com>
    ---
    include/linux/sched.h | 7 +++++++
    kernel/locking/mutex.c | 6 +++---
    2 files changed, 10 insertions(+), 3 deletions(-)

    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index bd995e66d7d6..379e4c052644 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -2201,6 +2201,13 @@ 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 __always_inline bool need_resched(void)
    {
    return unlikely(tif_need_resched());
    diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
    index f05cd2d216c7..7800380219db 100644
    --- a/kernel/locking/mutex.c
    +++ b/kernel/locking/mutex.c
    @@ -645,7 +645,7 @@ __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 (;;) {
    @@ -686,7 +686,7 @@ __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
    @@ -720,7 +720,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
    }

    __mutex_remove_waiter(lock, &waiter);
    - current->blocked_on = NULL;
    + set_task_blocked_on(current, NULL);

    debug_mutex_free_waiter(&waiter);

    --
    2.38.0.rc1.362.ged0d419d3c-goog
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