Merge "locking/qrwlock: Use atomic_cond_read_acquire() when spinning in qrwlock" (f8a29233) · Commits · e / devices / android_kernel_fairphone_FP3

include/asm-generic/qrwlock.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -49,7 +49,7 @@
		/*
		* External function declarations
		*/
		extern void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts);
		extern void queued_read_lock_slowpath(struct qrwlock *lock);
		extern void queued_write_lock_slowpath(struct qrwlock *lock);

		/**
		@@ -118,7 +118,7 @@ static inline void queued_read_lock(struct qrwlock *lock)
		return;

		/* The slowpath will decrement the reader count, if necessary. */
		queued_read_lock_slowpath(lock, cnts);
		queued_read_lock_slowpath(lock);
		}

		/**

kernel/locking/qrwlock.c

+12 −38

Original line number	Diff line number	Diff line
		@@ -22,29 +22,11 @@
		#include <linux/hardirq.h>
		#include <asm/qrwlock.h>

		/**
		* rspin_until_writer_unlock - inc reader count & spin until writer is gone
		* @lock : Pointer to queue rwlock structure
		* @writer: Current queue rwlock writer status byte
		*
		* In interrupt context or at the head of the queue, the reader will just
		* increment the reader count & wait until the writer releases the lock.
		*/
		static __always_inline void
		rspin_until_writer_unlock(struct qrwlock *lock, u32 cnts)
		{
		while ((cnts & _QW_WMASK) == _QW_LOCKED) {
		cpu_relax_lowlatency();
		cnts = atomic_read_acquire(&lock->cnts);
		}
		}

		/**
		* queued_read_lock_slowpath - acquire read lock of a queue rwlock
		* @lock: Pointer to queue rwlock structure
		* @cnts: Current qrwlock lock value
		*/
		void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts)
		void queued_read_lock_slowpath(struct qrwlock *lock)
		{
		/*
		* Readers come here when they cannot get the lock without waiting
		@@ -52,13 +34,12 @@ void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts)
		if (unlikely(in_interrupt())) {
		/*
		* Readers in interrupt context will get the lock immediately
		* if the writer is just waiting (not holding the lock yet).
		* The rspin_until_writer_unlock() function returns immediately
		* in this case. Otherwise, they will spin (with ACQUIRE
		* semantics) until the lock is available without waiting in
		* the queue.
		* if the writer is just waiting (not holding the lock yet),
		* so spin with ACQUIRE semantics until the lock is available
		* without waiting in the queue.
		*/
		rspin_until_writer_unlock(lock, cnts);
		atomic_cond_read_acquire(&lock->cnts, (VAL & _QW_WMASK)
		!= _QW_LOCKED);
		return;
		}
		atomic_sub(_QR_BIAS, &lock->cnts);
		@@ -67,14 +48,14 @@ void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts)
		* Put the reader into the wait queue
		*/
		arch_spin_lock(&lock->wait_lock);
		atomic_add(_QR_BIAS, &lock->cnts);

		/*
		* The ACQUIRE semantics of the following spinning code ensure
		* that accesses can't leak upwards out of our subsequent critical
		* section in the case that the lock is currently held for write.
		*/
		cnts = atomic_fetch_add_acquire(_QR_BIAS, &lock->cnts);
		rspin_until_writer_unlock(lock, cnts);
		atomic_cond_read_acquire(&lock->cnts, (VAL & _QW_WMASK) != _QW_LOCKED);

		/*
		* Signal the next one in queue to become queue head
		@@ -89,8 +70,6 @@ EXPORT_SYMBOL(queued_read_lock_slowpath);
		*/
		void queued_write_lock_slowpath(struct qrwlock *lock)
		{
		u32 cnts;

		/* Put the writer into the wait queue */
		arch_spin_lock(&lock->wait_lock);

		@@ -112,15 +91,10 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
		}

		/* When no more readers, set the locked flag */
		for (;;) {
		cnts = atomic_read(&lock->cnts);
		if ((cnts == _QW_WAITING) &&
		(atomic_cmpxchg_acquire(&lock->cnts, _QW_WAITING,
		_QW_LOCKED) == _QW_WAITING))
		break;

		cpu_relax_lowlatency();
		}
		do {
		atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING);
		} while (atomic_cmpxchg_relaxed(&lock->cnts, _QW_WAITING,
		_QW_LOCKED) != _QW_WAITING);
		unlock:
		arch_spin_unlock(&lock->wait_lock);
		}