Merge branch 'tip/locking/urgent' (3f48565b) · Commits · git / linux-nf

kernel/locking/rwbase_rt.c

+45 −20

Original line number	Diff line number	Diff line
		@@ -41,6 +41,12 @@
		* The risk of writer starvation is there, but the pathological use cases
		* which trigger it are not necessarily the typical RT workloads.
		*
		* Fast-path orderings:
		* The lock/unlock of readers can run in fast paths: lock and unlock are only
		* atomic ops, and there is no inner lock to provide ACQUIRE and RELEASE
		* semantics of rwbase_rt. Atomic ops should thus provide _acquire()
		* and _release() (or stronger).
		*
		* Common code shared between RT rw_semaphore and rwlock
		*/

		@@ -53,6 +59,7 @@ static __always_inline int rwbase_read_trylock(struct rwbase_rt *rwb)
		* set.
		*/
		for (r = atomic_read(&rwb->readers); r < 0;) {
		/* Fully-ordered if cmpxchg() succeeds, provides ACQUIRE */
		if (likely(atomic_try_cmpxchg(&rwb->readers, &r, r + 1)))
		return 1;
		}
		@@ -166,6 +173,8 @@ static __always_inline void rwbase_read_unlock(struct rwbase_rt *rwb,
		/*
		* rwb->readers can only hit 0 when a writer is waiting for the
		* active readers to leave the critical section.
		*
		* dec_and_test() is fully ordered, provides RELEASE.
		*/
		if (unlikely(atomic_dec_and_test(&rwb->readers)))
		__rwbase_read_unlock(rwb, state);
		@@ -176,7 +185,11 @@ static inline void __rwbase_write_unlock(struct rwbase_rt *rwb, int bias,
		{
		struct rt_mutex_base *rtm = &rwb->rtmutex;

		atomic_add(READER_BIAS - bias, &rwb->readers);
		/*
		* _release() is needed in case that reader is in fast path, pairing
		* with atomic_try_cmpxchg() in rwbase_read_trylock(), provides RELEASE
		*/
		(void)atomic_add_return_release(READER_BIAS - bias, &rwb->readers);
		raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
		rwbase_rtmutex_unlock(rtm);
		}
		@@ -200,6 +213,23 @@ static inline void rwbase_write_downgrade(struct rwbase_rt *rwb)
		__rwbase_write_unlock(rwb, WRITER_BIAS - 1, flags);
		}

		static inline bool __rwbase_write_trylock(struct rwbase_rt *rwb)
		{
		/* Can do without CAS because we're serialized by wait_lock. */
		lockdep_assert_held(&rwb->rtmutex.wait_lock);

		/*
		* _acquire is needed in case the reader is in the fast path, pairing
		* with rwbase_read_unlock(), provides ACQUIRE.
		*/
		if (!atomic_read_acquire(&rwb->readers)) {
		atomic_set(&rwb->readers, WRITER_BIAS);
		return 1;
		}

		return 0;
		}

		static int __sched rwbase_write_lock(struct rwbase_rt *rwb,
		unsigned int state)
		{
		@@ -214,34 +244,30 @@ static int __sched rwbase_write_lock(struct rwbase_rt *rwb,
		atomic_sub(READER_BIAS, &rwb->readers);

		raw_spin_lock_irqsave(&rtm->wait_lock, flags);
		/*
		* set_current_state() for rw_semaphore
		* current_save_and_set_rtlock_wait_state() for rwlock
		*/
		rwbase_set_and_save_current_state(state);
		if (__rwbase_write_trylock(rwb))
		goto out_unlock;

		/* Block until all readers have left the critical section. */
		for (; atomic_read(&rwb->readers);) {
		rwbase_set_and_save_current_state(state);
		for (;;) {
		/* Optimized out for rwlocks */
		if (rwbase_signal_pending_state(state, current)) {
		__set_current_state(TASK_RUNNING);
		rwbase_restore_current_state();
		__rwbase_write_unlock(rwb, 0, flags);
		return -EINTR;
		}
		raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);

		/*
		* Schedule and wait for the readers to leave the critical
		* section. The last reader leaving it wakes the waiter.
		*/
		if (atomic_read(&rwb->readers) != 0)
		if (__rwbase_write_trylock(rwb))
		break;

		raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
		rwbase_schedule();
		set_current_state(state);
		raw_spin_lock_irqsave(&rtm->wait_lock, flags);
		}

		atomic_set(&rwb->readers, WRITER_BIAS);
		set_current_state(state);
		}
		rwbase_restore_current_state();

		out_unlock:
		raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
		return 0;
		}
		@@ -257,8 +283,7 @@ static inline int rwbase_write_trylock(struct rwbase_rt *rwb)
		atomic_sub(READER_BIAS, &rwb->readers);

		raw_spin_lock_irqsave(&rtm->wait_lock, flags);
		if (!atomic_read(&rwb->readers)) {
		atomic_set(&rwb->readers, WRITER_BIAS);
		if (__rwbase_write_trylock(rwb)) {
		raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
		return 1;
		}