locking/qspinlock: Rework some comments (756b1df4) · Commits · 戴 / test

kernel/locking/qspinlock.c

+26 −10

Original line number	Diff line number	Diff line
		@@ -326,16 +326,23 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
		/*
		* trylock \|\| pending
		*
		* 0,0,0 -> 0,0,1 ; trylock
		* 0,0,1 -> 0,1,1 ; pending
		* 0,0,* -> 0,1,* -> 0,0,1 pending, trylock
		*/
		val = atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val);

		/*
		* If we observe any contention; undo and queue.
		* If we observe contention, there is a concurrent locker.
		*
		* Undo and queue; our setting of PENDING might have made the
		* n,0,0 -> 0,0,0 transition fail and it will now be waiting
		* on @next to become !NULL.
		*/
		if (unlikely(val & ~_Q_LOCKED_MASK)) {

		/* Undo PENDING if we set it. */
		if (!(val & _Q_PENDING_MASK))
		clear_pending(lock);

		goto queue;
		}

		@@ -474,16 +481,25 @@ locked:
		*/

		/*
		* In the PV case we might already have _Q_LOCKED_VAL set.
		* In the PV case we might already have _Q_LOCKED_VAL set, because
		* of lock stealing; therefore we must also allow:
		*
		* The atomic_cond_read_acquire() call above has provided the
		* necessary acquire semantics required for locking.
		* n,0,1 -> 0,0,1
		*
		* Note: at this point: (val & _Q_PENDING_MASK) == 0, because of the
		* above wait condition, therefore any concurrent setting of
		* PENDING will make the uncontended transition fail.
		*/
		if (((val & _Q_TAIL_MASK) == tail) &&
		atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL))
		if ((val & _Q_TAIL_MASK) == tail) {
		if (atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL))
		goto release; /* No contention */
		}

		/* Either somebody is queued behind us or _Q_PENDING_VAL is set */
		/*
		* Either somebody is queued behind us or _Q_PENDING_VAL got set
		* which will then detect the remaining tail and queue behind us
		* ensuring we'll see a @next.
		*/
		set_locked(lock);

		/*

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