Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1716 insertions, 0 deletions

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
new file mode 100644
index 0000000000..9eabd585ce
--- /dev/null
+++ b/kernel/locking/rwsem.c
@@ -0,0 +1,1716 @@
+// SPDX-License-Identifier: GPL-2.0
+/* kernel/rwsem.c: R/W semaphores, public implementation
+ *
+ * Written by David Howells (dhowells@redhat.com).
+ * Derived from asm-i386/semaphore.h
+ *
+ * Writer lock-stealing by Alex Shi <alex.shi@intel.com>
+ * and Michel Lespinasse <walken@google.com>
+ *
+ * Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
+ * and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
+ *
+ * Rwsem count bit fields re-definition and rwsem rearchitecture by
+ * Waiman Long <longman@redhat.com> and
+ * Peter Zijlstra <peterz@infradead.org>.
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/sched/rt.h>
+#include <linux/sched/task.h>
+#include <linux/sched/debug.h>
+#include <linux/sched/wake_q.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/clock.h>
+#include <linux/export.h>
+#include <linux/rwsem.h>
+#include <linux/atomic.h>
+#include <trace/events/lock.h>
+
+#ifndef CONFIG_PREEMPT_RT
+#include "lock_events.h"
+
+/*
+ * The least significant 2 bits of the owner value has the following
+ * meanings when set.
+ *  - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
+ *  - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
+ *
+ * When the rwsem is reader-owned and a spinning writer has timed out,
+ * the nonspinnable bit will be set to disable optimistic spinning.
+
+ * When a writer acquires a rwsem, it puts its task_struct pointer
+ * into the owner field. It is cleared after an unlock.
+ *
+ * When a reader acquires a rwsem, it will also puts its task_struct
+ * pointer into the owner field with the RWSEM_READER_OWNED bit set.
+ * On unlock, the owner field will largely be left untouched. So
+ * for a free or reader-owned rwsem, the owner value may contain
+ * information about the last reader that acquires the rwsem.
+ *
+ * That information may be helpful in debugging cases where the system
+ * seems to hang on a reader owned rwsem especially if only one reader
+ * is involved. Ideally we would like to track all the readers that own
+ * a rwsem, but the overhead is simply too big.
+ *
+ * A fast path reader optimistic lock stealing is supported when the rwsem
+ * is previously owned by a writer and the following conditions are met:
+ *  - rwsem is not currently writer owned
+ *  - the handoff isn't set.
+ */
+#define RWSEM_READER_OWNED	(1UL << 0)
+#define RWSEM_NONSPINNABLE	(1UL << 1)
+#define RWSEM_OWNER_FLAGS_MASK	(RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
+
+#ifdef CONFIG_DEBUG_RWSEMS
+# define DEBUG_RWSEMS_WARN_ON(c, sem)	do {			\
+	if (!debug_locks_silent &&				\
+	    WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
+		#c, atomic_long_read(&(sem)->count),		\
+		(unsigned long) sem->magic,			\
+		atomic_long_read(&(sem)->owner), (long)current,	\
+		list_empty(&(sem)->wait_list) ? "" : "not "))	\
+			debug_locks_off();			\
+	} while (0)
+#else
+# define DEBUG_RWSEMS_WARN_ON(c, sem)
+#endif
+
+/*
+ * On 64-bit architectures, the bit definitions of the count are:
+ *
+ * Bit  0    - writer locked bit
+ * Bit  1    - waiters present bit
+ * Bit  2    - lock handoff bit
+ * Bits 3-7  - reserved
+ * Bits 8-62 - 55-bit reader count
+ * Bit  63   - read fail bit
+ *
+ * On 32-bit architectures, the bit definitions of the count are:
+ *
+ * Bit  0    - writer locked bit
+ * Bit  1    - waiters present bit
+ * Bit  2    - lock handoff bit
+ * Bits 3-7  - reserved
+ * Bits 8-30 - 23-bit reader count
+ * Bit  31   - read fail bit
+ *
+ * It is not likely that the most significant bit (read fail bit) will ever
+ * be set. This guard bit is still checked anyway in the down_read() fastpath
+ * just in case we need to use up more of the reader bits for other purpose
+ * in the future.
+ *
+ * atomic_long_fetch_add() is used to obtain reader lock, whereas
+ * atomic_long_cmpxchg() will be used to obtain writer lock.
+ *
+ * There are three places where the lock handoff bit may be set or cleared.
+ * 1) rwsem_mark_wake() for readers		-- set, clear
+ * 2) rwsem_try_write_lock() for writers	-- set, clear
+ * 3) rwsem_del_waiter()			-- clear
+ *
+ * For all the above cases, wait_lock will be held. A writer must also
+ * be the first one in the wait_list to be eligible for setting the handoff
+ * bit. So concurrent setting/clearing of handoff bit is not possible.
+ */
+#define RWSEM_WRITER_LOCKED	(1UL << 0)
+#define RWSEM_FLAG_WAITERS	(1UL << 1)
+#define RWSEM_FLAG_HANDOFF	(1UL << 2)
+#define RWSEM_FLAG_READFAIL	(1UL << (BITS_PER_LONG - 1))
+
+#define RWSEM_READER_SHIFT	8
+#define RWSEM_READER_BIAS	(1UL << RWSEM_READER_SHIFT)
+#define RWSEM_READER_MASK	(~(RWSEM_READER_BIAS - 1))
+#define RWSEM_WRITER_MASK	RWSEM_WRITER_LOCKED
+#define RWSEM_LOCK_MASK		(RWSEM_WRITER_MASK|RWSEM_READER_MASK)
+#define RWSEM_READ_FAILED_MASK	(RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
+				 RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
+
+/*
+ * All writes to owner are protected by WRITE_ONCE() to make sure that
+ * store tearing can't happen as optimistic spinners may read and use
+ * the owner value concurrently without lock. Read from owner, however,
+ * may not need READ_ONCE() as long as the pointer value is only used
+ * for comparison and isn't being dereferenced.
+ *
+ * Both rwsem_{set,clear}_owner() functions should be in the same
+ * preempt disable section as the atomic op that changes sem->count.
+ */
+static inline void rwsem_set_owner(struct rw_semaphore *sem)
+{
+	lockdep_assert_preemption_disabled();
+	atomic_long_set(&sem->owner, (long)current);
+}
+
+static inline void rwsem_clear_owner(struct rw_semaphore *sem)
+{
+	lockdep_assert_preemption_disabled();
+	atomic_long_set(&sem->owner, 0);
+}
+
+/*
+ * Test the flags in the owner field.
+ */
+static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
+{
+	return atomic_long_read(&sem->owner) & flags;
+}
+
+/*
+ * The task_struct pointer of the last owning reader will be left in
+ * the owner field.
+ *
+ * Note that the owner value just indicates the task has owned the rwsem
+ * previously, it may not be the real owner or one of the real owners
+ * anymore when that field is examined, so take it with a grain of salt.
+ *
+ * The reader non-spinnable bit is preserved.
+ */
+static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
+					    struct task_struct *owner)
+{
+	unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
+		(atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
+
+	atomic_long_set(&sem->owner, val);
+}
+
+static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
+{
+	__rwsem_set_reader_owned(sem, current);
+}
+
+/*
+ * Return true if the rwsem is owned by a reader.
+ */
+static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
+{
+#ifdef CONFIG_DEBUG_RWSEMS
+	/*
+	 * Check the count to see if it is write-locked.
+	 */
+	long count = atomic_long_read(&sem->count);
+
+	if (count & RWSEM_WRITER_MASK)
+		return false;
+#endif
+	return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
+}
+
+#ifdef CONFIG_DEBUG_RWSEMS
+/*
+ * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
+ * is a task pointer in owner of a reader-owned rwsem, it will be the
+ * real owner or one of the real owners. The only exception is when the
+ * unlock is done by up_read_non_owner().
+ */
+static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
+{
+	unsigned long val = atomic_long_read(&sem->owner);
+
+	while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
+		if (atomic_long_try_cmpxchg(&sem->owner, &val,
+					    val & RWSEM_OWNER_FLAGS_MASK))
+			return;
+	}
+}
+#else
+static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
+{
+}
+#endif
+
+/*
+ * Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
+ * remains set. Otherwise, the operation will be aborted.
+ */
+static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
+{
+	unsigned long owner = atomic_long_read(&sem->owner);
+
+	do {
+		if (!(owner & RWSEM_READER_OWNED))
+			break;
+		if (owner & RWSEM_NONSPINNABLE)
+			break;
+	} while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
+					  owner | RWSEM_NONSPINNABLE));
+}
+
+static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
+{
+	*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
+
+	if (WARN_ON_ONCE(*cntp < 0))
+		rwsem_set_nonspinnable(sem);
+
+	if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
+		rwsem_set_reader_owned(sem);
+		return true;
+	}
+
+	return false;
+}
+
+static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
+{
+	long tmp = RWSEM_UNLOCKED_VALUE;
+
+	if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
+		rwsem_set_owner(sem);
+		return true;
+	}
+
+	return false;
+}
+
+/*
+ * Return just the real task structure pointer of the owner
+ */
+static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
+{
+	return (struct task_struct *)
+		(atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
+}
+
+/*
+ * Return the real task structure pointer of the owner and the embedded
+ * flags in the owner. pflags must be non-NULL.
+ */
+static inline struct task_struct *
+rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
+{
+	unsigned long owner = atomic_long_read(&sem->owner);
+
+	*pflags = owner & RWSEM_OWNER_FLAGS_MASK;
+	return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
+}
+
+/*
+ * Guide to the rw_semaphore's count field.
+ *
+ * When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
+ * by a writer.
+ *
+ * The lock is owned by readers when
+ * (1) the RWSEM_WRITER_LOCKED isn't set in count,
+ * (2) some of the reader bits are set in count, and
+ * (3) the owner field has RWSEM_READ_OWNED bit set.
+ *
+ * Having some reader bits set is not enough to guarantee a readers owned
+ * lock as the readers may be in the process of backing out from the count
+ * and a writer has just released the lock. So another writer may steal
+ * the lock immediately after that.
+ */
+
+/*
+ * Initialize an rwsem:
+ */
+void __init_rwsem(struct rw_semaphore *sem, const char *name,
+		  struct lock_class_key *key)
+{
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	/*
+	 * Make sure we are not reinitializing a held semaphore:
+	 */
+	debug_check_no_locks_freed((void *)sem, sizeof(*sem));
+	lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
+#endif
+#ifdef CONFIG_DEBUG_RWSEMS
+	sem->magic = sem;
+#endif
+	atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
+	raw_spin_lock_init(&sem->wait_lock);
+	INIT_LIST_HEAD(&sem->wait_list);
+	atomic_long_set(&sem->owner, 0L);
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
+	osq_lock_init(&sem->osq);
+#endif
+}
+EXPORT_SYMBOL(__init_rwsem);
+
+enum rwsem_waiter_type {
+	RWSEM_WAITING_FOR_WRITE,
+	RWSEM_WAITING_FOR_READ
+};
+
+struct rwsem_waiter {
+	struct list_head list;
+	struct task_struct *task;
+	enum rwsem_waiter_type type;
+	unsigned long timeout;
+	bool handoff_set;
+};
+#define rwsem_first_waiter(sem) \
+	list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
+
+enum rwsem_wake_type {
+	RWSEM_WAKE_ANY,		/* Wake whatever's at head of wait list */
+	RWSEM_WAKE_READERS,	/* Wake readers only */
+	RWSEM_WAKE_READ_OWNED	/* Waker thread holds the read lock */
+};
+
+/*
+ * The typical HZ value is either 250 or 1000. So set the minimum waiting
+ * time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
+ * queue before initiating the handoff protocol.
+ */
+#define RWSEM_WAIT_TIMEOUT	DIV_ROUND_UP(HZ, 250)
+
+/*
+ * Magic number to batch-wakeup waiting readers, even when writers are
+ * also present in the queue. This both limits the amount of work the
+ * waking thread must do and also prevents any potential counter overflow,
+ * however unlikely.
+ */
+#define MAX_READERS_WAKEUP	0x100
+
+static inline void
+rwsem_add_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
+{
+	lockdep_assert_held(&sem->wait_lock);
+	list_add_tail(&waiter->list, &sem->wait_list);
+	/* caller will set RWSEM_FLAG_WAITERS */
+}
+
+/*
+ * Remove a waiter from the wait_list and clear flags.
+ *
+ * Both rwsem_mark_wake() and rwsem_try_write_lock() contain a full 'copy' of
+ * this function. Modify with care.
+ *
+ * Return: true if wait_list isn't empty and false otherwise
+ */
+static inline bool
+rwsem_del_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
+{
+	lockdep_assert_held(&sem->wait_lock);
+	list_del(&waiter->list);
+	if (likely(!list_empty(&sem->wait_list)))
+		return true;
+
+	atomic_long_andnot(RWSEM_FLAG_HANDOFF | RWSEM_FLAG_WAITERS, &sem->count);
+	return false;
+}
+
+/*
+ * handle the lock release when processes blocked on it that can now run
+ * - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
+ *   have been set.
+ * - there must be someone on the queue
+ * - the wait_lock must be held by the caller
+ * - tasks are marked for wakeup, the caller must later invoke wake_up_q()
+ *   to actually wakeup the blocked task(s) and drop the reference count,
+ *   preferably when the wait_lock is released
+ * - woken process blocks are discarded from the list after having task zeroed
+ * - writers are only marked woken if downgrading is false
+ *
+ * Implies rwsem_del_waiter() for all woken readers.
+ */
+static void rwsem_mark_wake(struct rw_semaphore *sem,
+			    enum rwsem_wake_type wake_type,
+			    struct wake_q_head *wake_q)
+{
+	struct rwsem_waiter *waiter, *tmp;
+	long oldcount, woken = 0, adjustment = 0;
+	struct list_head wlist;
+
+	lockdep_assert_held(&sem->wait_lock);
+
+	/*
+	 * Take a peek at the queue head waiter such that we can determine
+	 * the wakeup(s) to perform.
+	 */
+	waiter = rwsem_first_waiter(sem);
+
+	if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
+		if (wake_type == RWSEM_WAKE_ANY) {
+			/*
+			 * Mark writer at the front of the queue for wakeup.
+			 * Until the task is actually later awoken later by
+			 * the caller, other writers are able to steal it.
+			 * Readers, on the other hand, will block as they
+			 * will notice the queued writer.
+			 */
+			wake_q_add(wake_q, waiter->task);
+			lockevent_inc(rwsem_wake_writer);
+		}
+
+		return;
+	}
+
+	/*
+	 * No reader wakeup if there are too many of them already.
+	 */
+	if (unlikely(atomic_long_read(&sem->count) < 0))
+		return;
+
+	/*
+	 * Writers might steal the lock before we grant it to the next reader.
+	 * We prefer to do the first reader grant before counting readers
+	 * so we can bail out early if a writer stole the lock.
+	 */
+	if (wake_type != RWSEM_WAKE_READ_OWNED) {
+		struct task_struct *owner;
+
+		adjustment = RWSEM_READER_BIAS;
+		oldcount = atomic_long_fetch_add(adjustment, &sem->count);
+		if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
+			/*
+			 * When we've been waiting "too" long (for writers
+			 * to give up the lock), request a HANDOFF to
+			 * force the issue.
+			 */
+			if (time_after(jiffies, waiter->timeout)) {
+				if (!(oldcount & RWSEM_FLAG_HANDOFF)) {
+					adjustment -= RWSEM_FLAG_HANDOFF;
+					lockevent_inc(rwsem_rlock_handoff);
+				}
+				waiter->handoff_set = true;
+			}
+
+			atomic_long_add(-adjustment, &sem->count);
+			return;
+		}
+		/*
+		 * Set it to reader-owned to give spinners an early
+		 * indication that readers now have the lock.
+		 * The reader nonspinnable bit seen at slowpath entry of
+		 * the reader is copied over.
+		 */
+		owner = waiter->task;
+		__rwsem_set_reader_owned(sem, owner);
+	}
+
+	/*
+	 * Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
+	 * queue. We know that the woken will be at least 1 as we accounted
+	 * for above. Note we increment the 'active part' of the count by the
+	 * number of readers before waking any processes up.
+	 *
+	 * This is an adaptation of the phase-fair R/W locks where at the
+	 * reader phase (first waiter is a reader), all readers are eligible
+	 * to acquire the lock at the same time irrespective of their order
+	 * in the queue. The writers acquire the lock according to their
+	 * order in the queue.
+	 *
+	 * We have to do wakeup in 2 passes to prevent the possibility that
+	 * the reader count may be decremented before it is incremented. It
+	 * is because the to-be-woken waiter may not have slept yet. So it
+	 * may see waiter->task got cleared, finish its critical section and
+	 * do an unlock before the reader count increment.
+	 *
+	 * 1) Collect the read-waiters in a separate list, count them and
+	 *    fully increment the reader count in rwsem.
+	 * 2) For each waiters in the new list, clear waiter->task and
+	 *    put them into wake_q to be woken up later.
+	 */
+	INIT_LIST_HEAD(&wlist);
+	list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
+		if (waiter->type == RWSEM_WAITING_FOR_WRITE)
+			continue;
+
+		woken++;
+		list_move_tail(&waiter->list, &wlist);
+
+		/*
+		 * Limit # of readers that can be woken up per wakeup call.
+		 */
+		if (unlikely(woken >= MAX_READERS_WAKEUP))
+			break;
+	}
+
+	adjustment = woken * RWSEM_READER_BIAS - adjustment;
+	lockevent_cond_inc(rwsem_wake_reader, woken);
+
+	oldcount = atomic_long_read(&sem->count);
+	if (list_empty(&sem->wait_list)) {
+		/*
+		 * Combined with list_move_tail() above, this implies
+		 * rwsem_del_waiter().
+		 */
+		adjustment -= RWSEM_FLAG_WAITERS;
+		if (oldcount & RWSEM_FLAG_HANDOFF)
+			adjustment -= RWSEM_FLAG_HANDOFF;
+	} else if (woken) {
+		/*
+		 * When we've woken a reader, we no longer need to force
+		 * writers to give up the lock and we can clear HANDOFF.
+		 */
+		if (oldcount & RWSEM_FLAG_HANDOFF)
+			adjustment -= RWSEM_FLAG_HANDOFF;
+	}
+
+	if (adjustment)
+		atomic_long_add(adjustment, &sem->count);
+
+	/* 2nd pass */
+	list_for_each_entry_safe(waiter, tmp, &wlist, list) {
+		struct task_struct *tsk;
+
+		tsk = waiter->task;
+		get_task_struct(tsk);
+
+		/*
+		 * Ensure calling get_task_struct() before setting the reader
+		 * waiter to nil such that rwsem_down_read_slowpath() cannot
+		 * race with do_exit() by always holding a reference count
+		 * to the task to wakeup.
+		 */
+		smp_store_release(&waiter->task, NULL);
+		/*
+		 * Ensure issuing the wakeup (either by us or someone else)
+		 * after setting the reader waiter to nil.
+		 */
+		wake_q_add_safe(wake_q, tsk);
+	}
+}
+
+/*
+ * Remove a waiter and try to wake up other waiters in the wait queue
+ * This function is called from the out_nolock path of both the reader and
+ * writer slowpaths with wait_lock held. It releases the wait_lock and
+ * optionally wake up waiters before it returns.
+ */
+static inline void
+rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter,
+		      struct wake_q_head *wake_q)
+		      __releases(&sem->wait_lock)
+{
+	bool first = rwsem_first_waiter(sem) == waiter;
+
+	wake_q_init(wake_q);
+
+	/*
+	 * If the wait_list isn't empty and the waiter to be deleted is
+	 * the first waiter, we wake up the remaining waiters as they may
+	 * be eligible to acquire or spin on the lock.
+	 */
+	if (rwsem_del_waiter(sem, waiter) && first)
+		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, wake_q);
+	raw_spin_unlock_irq(&sem->wait_lock);
+	if (!wake_q_empty(wake_q))
+		wake_up_q(wake_q);
+}
+
+/*
+ * This function must be called with the sem->wait_lock held to prevent
+ * race conditions between checking the rwsem wait list and setting the
+ * sem->count accordingly.
+ *
+ * Implies rwsem_del_waiter() on success.
+ */
+static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
+					struct rwsem_waiter *waiter)
+{
+	struct rwsem_waiter *first = rwsem_first_waiter(sem);
+	long count, new;
+
+	lockdep_assert_held(&sem->wait_lock);
+
+	count = atomic_long_read(&sem->count);
+	do {
+		bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
+
+		if (has_handoff) {
+			/*
+			 * Honor handoff bit and yield only when the first
+			 * waiter is the one that set it. Otherwisee, we
+			 * still try to acquire the rwsem.
+			 */
+			if (first->handoff_set && (waiter != first))
+				return false;
+		}
+
+		new = count;
+
+		if (count & RWSEM_LOCK_MASK) {
+			/*
+			 * A waiter (first or not) can set the handoff bit
+			 * if it is an RT task or wait in the wait queue
+			 * for too long.
+			 */
+			if (has_handoff || (!rt_task(waiter->task) &&
+					    !time_after(jiffies, waiter->timeout)))
+				return false;
+
+			new |= RWSEM_FLAG_HANDOFF;
+		} else {
+			new |= RWSEM_WRITER_LOCKED;
+			new &= ~RWSEM_FLAG_HANDOFF;
+
+			if (list_is_singular(&sem->wait_list))
+				new &= ~RWSEM_FLAG_WAITERS;
+		}
+	} while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
+
+	/*
+	 * We have either acquired the lock with handoff bit cleared or set
+	 * the handoff bit. Only the first waiter can have its handoff_set
+	 * set here to enable optimistic spinning in slowpath loop.
+	 */
+	if (new & RWSEM_FLAG_HANDOFF) {
+		first->handoff_set = true;
+		lockevent_inc(rwsem_wlock_handoff);
+		return false;
+	}
+
+	/*
+	 * Have rwsem_try_write_lock() fully imply rwsem_del_waiter() on
+	 * success.
+	 */
+	list_del(&waiter->list);
+	rwsem_set_owner(sem);
+	return true;
+}
+
+/*
+ * The rwsem_spin_on_owner() function returns the following 4 values
+ * depending on the lock owner state.
+ *   OWNER_NULL  : owner is currently NULL
+ *   OWNER_WRITER: when owner changes and is a writer
+ *   OWNER_READER: when owner changes and the new owner may be a reader.
+ *   OWNER_NONSPINNABLE:
+ *		   when optimistic spinning has to stop because either the
+ *		   owner stops running, is unknown, or its timeslice has
+ *		   been used up.
+ */
+enum owner_state {
+	OWNER_NULL		= 1 << 0,
+	OWNER_WRITER		= 1 << 1,
+	OWNER_READER		= 1 << 2,
+	OWNER_NONSPINNABLE	= 1 << 3,
+};
+
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
+/*
+ * Try to acquire write lock before the writer has been put on wait queue.
+ */
+static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
+{
+	long count = atomic_long_read(&sem->count);
+
+	while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
+		if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
+					count | RWSEM_WRITER_LOCKED)) {
+			rwsem_set_owner(sem);
+			lockevent_inc(rwsem_opt_lock);
+			return true;
+		}
+	}
+	return false;
+}
+
+static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
+{
+	struct task_struct *owner;
+	unsigned long flags;
+	bool ret = true;
+
+	if (need_resched()) {
+		lockevent_inc(rwsem_opt_fail);
+		return false;
+	}
+
+	/*
+	 * Disable preemption is equal to the RCU read-side crital section,
+	 * thus the task_strcut structure won't go away.
+	 */
+	owner = rwsem_owner_flags(sem, &flags);
+	/*
+	 * Don't check the read-owner as the entry may be stale.
+	 */
+	if ((flags & RWSEM_NONSPINNABLE) ||
+	    (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
+		ret = false;
+
+	lockevent_cond_inc(rwsem_opt_fail, !ret);
+	return ret;
+}
+
+#define OWNER_SPINNABLE		(OWNER_NULL | OWNER_WRITER | OWNER_READER)
+
+static inline enum owner_state
+rwsem_owner_state(struct task_struct *owner, unsigned long flags)
+{
+	if (flags & RWSEM_NONSPINNABLE)
+		return OWNER_NONSPINNABLE;
+
+	if (flags & RWSEM_READER_OWNED)
+		return OWNER_READER;
+
+	return owner ? OWNER_WRITER : OWNER_NULL;
+}
+
+static noinline enum owner_state
+rwsem_spin_on_owner(struct rw_semaphore *sem)
+{
+	struct task_struct *new, *owner;
+	unsigned long flags, new_flags;
+	enum owner_state state;
+
+	lockdep_assert_preemption_disabled();
+
+	owner = rwsem_owner_flags(sem, &flags);
+	state = rwsem_owner_state(owner, flags);
+	if (state != OWNER_WRITER)
+		return state;
+
+	for (;;) {
+		/*
+		 * When a waiting writer set the handoff flag, it may spin
+		 * on the owner as well. Once that writer acquires the lock,
+		 * we can spin on it. So we don't need to quit even when the
+		 * handoff bit is set.
+		 */
+		new = rwsem_owner_flags(sem, &new_flags);
+		if ((new != owner) || (new_flags != flags)) {
+			state = rwsem_owner_state(new, new_flags);
+			break;
+		}
+
+		/*
+		 * Ensure we emit the owner->on_cpu, dereference _after_
+		 * checking sem->owner still matches owner, if that fails,
+		 * owner might point to free()d memory, if it still matches,
+		 * our spinning context already disabled preemption which is
+		 * equal to RCU read-side crital section ensures the memory
+		 * stays valid.
+		 */
+		barrier();
+
+		if (need_resched() || !owner_on_cpu(owner)) {
+			state = OWNER_NONSPINNABLE;
+			break;
+		}
+
+		cpu_relax();
+	}
+
+	return state;
+}
+
+/*
+ * Calculate reader-owned rwsem spinning threshold for writer
+ *
+ * The more readers own the rwsem, the longer it will take for them to
+ * wind down and free the rwsem. So the empirical formula used to
+ * determine the actual spinning time limit here is:
+ *
+ *   Spinning threshold = (10 + nr_readers/2)us
+ *
+ * The limit is capped to a maximum of 25us (30 readers). This is just
+ * a heuristic and is subjected to change in the future.
+ */
+static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
+{
+	long count = atomic_long_read(&sem->count);
+	int readers = count >> RWSEM_READER_SHIFT;
+	u64 delta;
+
+	if (readers > 30)
+		readers = 30;
+	delta = (20 + readers) * NSEC_PER_USEC / 2;
+
+	return sched_clock() + delta;
+}
+
+static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
+{
+	bool taken = false;
+	int prev_owner_state = OWNER_NULL;
+	int loop = 0;
+	u64 rspin_threshold = 0;
+
+	/* sem->wait_lock should not be held when doing optimistic spinning */
+	if (!osq_lock(&sem->osq))
+		goto done;
+
+	/*
+	 * Optimistically spin on the owner field and attempt to acquire the
+	 * lock whenever the owner changes. Spinning will be stopped when:
+	 *  1) the owning writer isn't running; or
+	 *  2) readers own the lock and spinning time has exceeded limit.
+	 */
+	for (;;) {
+		enum owner_state owner_state;
+
+		owner_state = rwsem_spin_on_owner(sem);
+		if (!(owner_state & OWNER_SPINNABLE))
+			break;
+
+		/*
+		 * Try to acquire the lock
+		 */
+		taken = rwsem_try_write_lock_unqueued(sem);
+
+		if (taken)
+			break;
+
+		/*
+		 * Time-based reader-owned rwsem optimistic spinning
+		 */
+		if (owner_state == OWNER_READER) {
+			/*
+			 * Re-initialize rspin_threshold every time when
+			 * the owner state changes from non-reader to reader.
+			 * This allows a writer to steal the lock in between
+			 * 2 reader phases and have the threshold reset at
+			 * the beginning of the 2nd reader phase.
+			 */
+			if (prev_owner_state != OWNER_READER) {
+				if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
+					break;
+				rspin_threshold = rwsem_rspin_threshold(sem);
+				loop = 0;
+			}
+
+			/*
+			 * Check time threshold once every 16 iterations to
+			 * avoid calling sched_clock() too frequently so
+			 * as to reduce the average latency between the times
+			 * when the lock becomes free and when the spinner
+			 * is ready to do a trylock.
+			 */
+			else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
+				rwsem_set_nonspinnable(sem);
+				lockevent_inc(rwsem_opt_nospin);
+				break;
+			}
+		}
+
+		/*
+		 * An RT task cannot do optimistic spinning if it cannot
+		 * be sure the lock holder is running or live-lock may
+		 * happen if the current task and the lock holder happen
+		 * to run in the same CPU. However, aborting optimistic
+		 * spinning while a NULL owner is detected may miss some
+		 * opportunity where spinning can continue without causing
+		 * problem.
+		 *
+		 * There are 2 possible cases where an RT task may be able
+		 * to continue spinning.
+		 *
+		 * 1) The lock owner is in the process of releasing the
+		 *    lock, sem->owner is cleared but the lock has not
+		 *    been released yet.
+		 * 2) The lock was free and owner cleared, but another
+		 *    task just comes in and acquire the lock before
+		 *    we try to get it. The new owner may be a spinnable
+		 *    writer.
+		 *
+		 * To take advantage of two scenarios listed above, the RT
+		 * task is made to retry one more time to see if it can
+		 * acquire the lock or continue spinning on the new owning
+		 * writer. Of course, if the time lag is long enough or the
+		 * new owner is not a writer or spinnable, the RT task will
+		 * quit spinning.
+		 *
+		 * If the owner is a writer, the need_resched() check is
+		 * done inside rwsem_spin_on_owner(). If the owner is not
+		 * a writer, need_resched() check needs to be done here.
+		 */
+		if (owner_state != OWNER_WRITER) {
+			if (need_resched())
+				break;
+			if (rt_task(current) &&
+			   (prev_owner_state != OWNER_WRITER))
+				break;
+		}
+		prev_owner_state = owner_state;
+
+		/*
+		 * The cpu_relax() call is a compiler barrier which forces
+		 * everything in this loop to be re-loaded. We don't need
+		 * memory barriers as we'll eventually observe the right
+		 * values at the cost of a few extra spins.
+		 */
+		cpu_relax();
+	}
+	osq_unlock(&sem->osq);
+done:
+	lockevent_cond_inc(rwsem_opt_fail, !taken);
+	return taken;
+}
+
+/*
+ * Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should
+ * only be called when the reader count reaches 0.
+ */
+static inline void clear_nonspinnable(struct rw_semaphore *sem)
+{
+	if (unlikely(rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)))
+		atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);
+}
+
+#else
+static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
+{
+	return false;
+}
+
+static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem)
+{
+	return false;
+}
+
+static inline void clear_nonspinnable(struct rw_semaphore *sem) { }
+
+static inline enum owner_state
+rwsem_spin_on_owner(struct rw_semaphore *sem)
+{
+	return OWNER_NONSPINNABLE;
+}
+#endif
+
+/*
+ * Prepare to wake up waiter(s) in the wait queue by putting them into the
+ * given wake_q if the rwsem lock owner isn't a writer. If rwsem is likely
+ * reader-owned, wake up read lock waiters in queue front or wake up any
+ * front waiter otherwise.
+
+ * This is being called from both reader and writer slow paths.
+ */
+static inline void rwsem_cond_wake_waiter(struct rw_semaphore *sem, long count,
+					  struct wake_q_head *wake_q)
+{
+	enum rwsem_wake_type wake_type;
+
+	if (count & RWSEM_WRITER_MASK)
+		return;
+
+	if (count & RWSEM_READER_MASK) {
+		wake_type = RWSEM_WAKE_READERS;
+	} else {
+		wake_type = RWSEM_WAKE_ANY;
+		clear_nonspinnable(sem);
+	}
+	rwsem_mark_wake(sem, wake_type, wake_q);
+}
+
+/*
+ * Wait for the read lock to be granted
+ */
+static struct rw_semaphore __sched *
+rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int state)
+{
+	long adjustment = -RWSEM_READER_BIAS;
+	long rcnt = (count >> RWSEM_READER_SHIFT);
+	struct rwsem_waiter waiter;
+	DEFINE_WAKE_Q(wake_q);
+
+	/*
+	 * To prevent a constant stream of readers from starving a sleeping
+	 * waiter, don't attempt optimistic lock stealing if the lock is
+	 * currently owned by readers.
+	 */
+	if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
+	    (rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
+		goto queue;
+
+	/*
+	 * Reader optimistic lock stealing.
+	 */
+	if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {
+		rwsem_set_reader_owned(sem);
+		lockevent_inc(rwsem_rlock_steal);
+
+		/*
+		 * Wake up other readers in the wait queue if it is
+		 * the first reader.
+		 */
+		if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) {
+			raw_spin_lock_irq(&sem->wait_lock);
+			if (!list_empty(&sem->wait_list))
+				rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
+						&wake_q);
+			raw_spin_unlock_irq(&sem->wait_lock);
+			wake_up_q(&wake_q);
+		}
+		return sem;
+	}
+
+queue:
+	waiter.task = current;
+	waiter.type = RWSEM_WAITING_FOR_READ;
+	waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
+	waiter.handoff_set = false;
+
+	raw_spin_lock_irq(&sem->wait_lock);
+	if (list_empty(&sem->wait_list)) {
+		/*
+		 * In case the wait queue is empty and the lock isn't owned
+		 * by a writer, this reader can exit the slowpath and return
+		 * immediately as its RWSEM_READER_BIAS has already been set
+		 * in the count.
+		 */
+		if (!(atomic_long_read(&sem->count) & RWSEM_WRITER_MASK)) {
+			/* Provide lock ACQUIRE */
+			smp_acquire__after_ctrl_dep();
+			raw_spin_unlock_irq(&sem->wait_lock);
+			rwsem_set_reader_owned(sem);
+			lockevent_inc(rwsem_rlock_fast);
+			return sem;
+		}
+		adjustment += RWSEM_FLAG_WAITERS;
+	}
+	rwsem_add_waiter(sem, &waiter);
+
+	/* we're now waiting on the lock, but no longer actively locking */
+	count = atomic_long_add_return(adjustment, &sem->count);
+
+	rwsem_cond_wake_waiter(sem, count, &wake_q);
+	raw_spin_unlock_irq(&sem->wait_lock);
+
+	if (!wake_q_empty(&wake_q))
+		wake_up_q(&wake_q);
+
+	trace_contention_begin(sem, LCB_F_READ);
+
+	/* wait to be given the lock */
+	for (;;) {
+		set_current_state(state);
+		if (!smp_load_acquire(&waiter.task)) {
+			/* Matches rwsem_mark_wake()'s smp_store_release(). */
+			break;
+		}
+		if (signal_pending_state(state, current)) {
+			raw_spin_lock_irq(&sem->wait_lock);
+			if (waiter.task)
+				goto out_nolock;
+			raw_spin_unlock_irq(&sem->wait_lock);
+			/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
+			break;
+		}
+		schedule_preempt_disabled();
+		lockevent_inc(rwsem_sleep_reader);
+	}
+
+	__set_current_state(TASK_RUNNING);
+	lockevent_inc(rwsem_rlock);
+	trace_contention_end(sem, 0);
+	return sem;
+
+out_nolock:
+	rwsem_del_wake_waiter(sem, &waiter, &wake_q);
+	__set_current_state(TASK_RUNNING);
+	lockevent_inc(rwsem_rlock_fail);
+	trace_contention_end(sem, -EINTR);
+	return ERR_PTR(-EINTR);
+}
+
+/*
+ * Wait until we successfully acquire the write lock
+ */
+static struct rw_semaphore __sched *
+rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
+{
+	struct rwsem_waiter waiter;
+	DEFINE_WAKE_Q(wake_q);
+
+	/* do optimistic spinning and steal lock if possible */
+	if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) {
+		/* rwsem_optimistic_spin() implies ACQUIRE on success */
+		return sem;
+	}
+
+	/*
+	 * Optimistic spinning failed, proceed to the slowpath
+	 * and block until we can acquire the sem.
+	 */
+	waiter.task = current;
+	waiter.type = RWSEM_WAITING_FOR_WRITE;
+	waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
+	waiter.handoff_set = false;
+
+	raw_spin_lock_irq(&sem->wait_lock);
+	rwsem_add_waiter(sem, &waiter);
+
+	/* we're now waiting on the lock */
+	if (rwsem_first_waiter(sem) != &waiter) {
+		rwsem_cond_wake_waiter(sem, atomic_long_read(&sem->count),
+				       &wake_q);
+		if (!wake_q_empty(&wake_q)) {
+			/*
+			 * We want to minimize wait_lock hold time especially
+			 * when a large number of readers are to be woken up.
+			 */
+			raw_spin_unlock_irq(&sem->wait_lock);
+			wake_up_q(&wake_q);
+			raw_spin_lock_irq(&sem->wait_lock);
+		}
+	} else {
+		atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
+	}
+
+	/* wait until we successfully acquire the lock */
+	set_current_state(state);
+	trace_contention_begin(sem, LCB_F_WRITE);
+
+	for (;;) {
+		if (rwsem_try_write_lock(sem, &waiter)) {
+			/* rwsem_try_write_lock() implies ACQUIRE on success */
+			break;
+		}
+
+		raw_spin_unlock_irq(&sem->wait_lock);
+
+		if (signal_pending_state(state, current))
+			goto out_nolock;
+
+		/*
+		 * After setting the handoff bit and failing to acquire
+		 * the lock, attempt to spin on owner to accelerate lock
+		 * transfer. If the previous owner is a on-cpu writer and it
+		 * has just released the lock, OWNER_NULL will be returned.
+		 * In this case, we attempt to acquire the lock again
+		 * without sleeping.
+		 */
+		if (waiter.handoff_set) {
+			enum owner_state owner_state;
+
+			owner_state = rwsem_spin_on_owner(sem);
+			if (owner_state == OWNER_NULL)
+				goto trylock_again;
+		}
+
+		schedule_preempt_disabled();
+		lockevent_inc(rwsem_sleep_writer);
+		set_current_state(state);
+trylock_again:
+		raw_spin_lock_irq(&sem->wait_lock);
+	}
+	__set_current_state(TASK_RUNNING);
+	raw_spin_unlock_irq(&sem->wait_lock);
+	lockevent_inc(rwsem_wlock);
+	trace_contention_end(sem, 0);
+	return sem;
+
+out_nolock:
+	__set_current_state(TASK_RUNNING);
+	raw_spin_lock_irq(&sem->wait_lock);
+	rwsem_del_wake_waiter(sem, &waiter, &wake_q);
+	lockevent_inc(rwsem_wlock_fail);
+	trace_contention_end(sem, -EINTR);
+	return ERR_PTR(-EINTR);
+}
+
+/*
+ * handle waking up a waiter on the semaphore
+ * - up_read/up_write has decremented the active part of count if we come here
+ */
+static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
+{
+	unsigned long flags;
+	DEFINE_WAKE_Q(wake_q);
+
+	raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+	if (!list_empty(&sem->wait_list))
+		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
+
+	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+	wake_up_q(&wake_q);
+
+	return sem;
+}
+
+/*
+ * downgrade a write lock into a read lock
+ * - caller incremented waiting part of count and discovered it still negative
+ * - just wake up any readers at the front of the queue
+ */
+static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
+{
+	unsigned long flags;
+	DEFINE_WAKE_Q(wake_q);
+
+	raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+	if (!list_empty(&sem->wait_list))
+		rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
+
+	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+	wake_up_q(&wake_q);
+
+	return sem;
+}
+
+/*
+ * lock for reading
+ */
+static __always_inline int __down_read_common(struct rw_semaphore *sem, int state)
+{
+	int ret = 0;
+	long count;
+
+	preempt_disable();
+	if (!rwsem_read_trylock(sem, &count)) {
+		if (IS_ERR(rwsem_down_read_slowpath(sem, count, state))) {
+			ret = -EINTR;
+			goto out;
+		}
+		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
+	}
+out:
+	preempt_enable();
+	return ret;
+}
+
+static __always_inline void __down_read(struct rw_semaphore *sem)
+{
+	__down_read_common(sem, TASK_UNINTERRUPTIBLE);
+}
+
+static __always_inline int __down_read_interruptible(struct rw_semaphore *sem)
+{
+	return __down_read_common(sem, TASK_INTERRUPTIBLE);
+}
+
+static __always_inline int __down_read_killable(struct rw_semaphore *sem)
+{
+	return __down_read_common(sem, TASK_KILLABLE);
+}
+
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+	int ret = 0;
+	long tmp;
+
+	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
+
+	preempt_disable();
+	tmp = atomic_long_read(&sem->count);
+	while (!(tmp & RWSEM_READ_FAILED_MASK)) {
+		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
+						    tmp + RWSEM_READER_BIAS)) {
+			rwsem_set_reader_owned(sem);
+			ret = 1;
+			break;
+		}
+	}
+	preempt_enable();
+	return ret;
+}
+
+/*
+ * lock for writing
+ */
+static inline int __down_write_common(struct rw_semaphore *sem, int state)
+{
+	int ret = 0;
+
+	preempt_disable();
+	if (unlikely(!rwsem_write_trylock(sem))) {
+		if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
+			ret = -EINTR;
+	}
+	preempt_enable();
+	return ret;
+}
+
+static inline void __down_write(struct rw_semaphore *sem)
+{
+	__down_write_common(sem, TASK_UNINTERRUPTIBLE);
+}
+
+static inline int __down_write_killable(struct rw_semaphore *sem)
+{
+	return __down_write_common(sem, TASK_KILLABLE);
+}
+
+static inline int __down_write_trylock(struct rw_semaphore *sem)
+{
+	int ret;
+
+	preempt_disable();
+	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
+	ret = rwsem_write_trylock(sem);
+	preempt_enable();
+
+	return ret;
+}
+
+/*
+ * unlock after reading
+ */
+static inline void __up_read(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
+	DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
+
+	preempt_disable();
+	rwsem_clear_reader_owned(sem);
+	tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
+	DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
+	if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
+		      RWSEM_FLAG_WAITERS)) {
+		clear_nonspinnable(sem);
+		rwsem_wake(sem);
+	}
+	preempt_enable();
+}
+
+/*
+ * unlock after writing
+ */
+static inline void __up_write(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
+	/*
+	 * sem->owner may differ from current if the ownership is transferred
+	 * to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
+	 */
+	DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
+			    !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
+
+	preempt_disable();
+	rwsem_clear_owner(sem);
+	tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
+	if (unlikely(tmp & RWSEM_FLAG_WAITERS))
+		rwsem_wake(sem);
+	preempt_enable();
+}
+
+/*
+ * downgrade write lock to read lock
+ */
+static inline void __downgrade_write(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	/*
+	 * When downgrading from exclusive to shared ownership,
+	 * anything inside the write-locked region cannot leak
+	 * into the read side. In contrast, anything in the
+	 * read-locked region is ok to be re-ordered into the
+	 * write side. As such, rely on RELEASE semantics.
+	 */
+	DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
+	preempt_disable();
+	tmp = atomic_long_fetch_add_release(
+		-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
+	rwsem_set_reader_owned(sem);
+	if (tmp & RWSEM_FLAG_WAITERS)
+		rwsem_downgrade_wake(sem);
+	preempt_enable();
+}
+
+#else /* !CONFIG_PREEMPT_RT */
+
+#define RT_MUTEX_BUILD_MUTEX
+#include "rtmutex.c"
+
+#define rwbase_set_and_save_current_state(state)	\
+	set_current_state(state)
+
+#define rwbase_restore_current_state()			\
+	__set_current_state(TASK_RUNNING)
+
+#define rwbase_rtmutex_lock_state(rtm, state)		\
+	__rt_mutex_lock(rtm, state)
+
+#define rwbase_rtmutex_slowlock_locked(rtm, state)	\
+	__rt_mutex_slowlock_locked(rtm, NULL, state)
+
+#define rwbase_rtmutex_unlock(rtm)			\
+	__rt_mutex_unlock(rtm)
+
+#define rwbase_rtmutex_trylock(rtm)			\
+	__rt_mutex_trylock(rtm)
+
+#define rwbase_signal_pending_state(state, current)	\
+	signal_pending_state(state, current)
+
+#define rwbase_schedule()				\
+	schedule()
+
+#include "rwbase_rt.c"
+
+void __init_rwsem(struct rw_semaphore *sem, const char *name,
+		  struct lock_class_key *key)
+{
+	init_rwbase_rt(&(sem)->rwbase);
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	debug_check_no_locks_freed((void *)sem, sizeof(*sem));
+	lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
+#endif
+}
+EXPORT_SYMBOL(__init_rwsem);
+
+static inline void __down_read(struct rw_semaphore *sem)
+{
+	rwbase_read_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
+}
+
+static inline int __down_read_interruptible(struct rw_semaphore *sem)
+{
+	return rwbase_read_lock(&sem->rwbase, TASK_INTERRUPTIBLE);
+}
+
+static inline int __down_read_killable(struct rw_semaphore *sem)
+{
+	return rwbase_read_lock(&sem->rwbase, TASK_KILLABLE);
+}
+
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+	return rwbase_read_trylock(&sem->rwbase);
+}
+
+static inline void __up_read(struct rw_semaphore *sem)
+{
+	rwbase_read_unlock(&sem->rwbase, TASK_NORMAL);
+}
+
+static inline void __sched __down_write(struct rw_semaphore *sem)
+{
+	rwbase_write_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
+}
+
+static inline int __sched __down_write_killable(struct rw_semaphore *sem)
+{
+	return rwbase_write_lock(&sem->rwbase, TASK_KILLABLE);
+}
+
+static inline int __down_write_trylock(struct rw_semaphore *sem)
+{
+	return rwbase_write_trylock(&sem->rwbase);
+}
+
+static inline void __up_write(struct rw_semaphore *sem)
+{
+	rwbase_write_unlock(&sem->rwbase);
+}
+
+static inline void __downgrade_write(struct rw_semaphore *sem)
+{
+	rwbase_write_downgrade(&sem->rwbase);
+}
+
+/* Debug stubs for the common API */
+#define DEBUG_RWSEMS_WARN_ON(c, sem)
+
+static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
+					    struct task_struct *owner)
+{
+}
+
+static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
+{
+	int count = atomic_read(&sem->rwbase.readers);
+
+	return count < 0 && count != READER_BIAS;
+}
+
+#endif /* CONFIG_PREEMPT_RT */
+
+/*
+ * lock for reading
+ */
+void __sched down_read(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
+
+	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
+}
+EXPORT_SYMBOL(down_read);
+
+int __sched down_read_interruptible(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
+
+	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
+		rwsem_release(&sem->dep_map, _RET_IP_);
+		return -EINTR;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(down_read_interruptible);
+
+int __sched down_read_killable(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
+
+	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
+		rwsem_release(&sem->dep_map, _RET_IP_);
+		return -EINTR;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(down_read_killable);
+
+/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+int down_read_trylock(struct rw_semaphore *sem)
+{
+	int ret = __down_read_trylock(sem);
+
+	if (ret == 1)
+		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
+	return ret;
+}
+EXPORT_SYMBOL(down_read_trylock);
+
+/*
+ * lock for writing
+ */
+void __sched down_write(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
+	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
+}
+EXPORT_SYMBOL(down_write);
+
+/*
+ * lock for writing
+ */
+int __sched down_write_killable(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
+
+	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
+				  __down_write_killable)) {
+		rwsem_release(&sem->dep_map, _RET_IP_);
+		return -EINTR;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(down_write_killable);
+
+/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+int down_write_trylock(struct rw_semaphore *sem)
+{
+	int ret = __down_write_trylock(sem);
+
+	if (ret == 1)
+		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
+
+	return ret;
+}
+EXPORT_SYMBOL(down_write_trylock);
+
+/*
+ * release a read lock
+ */
+void up_read(struct rw_semaphore *sem)
+{
+	rwsem_release(&sem->dep_map, _RET_IP_);
+	__up_read(sem);
+}
+EXPORT_SYMBOL(up_read);
+
+/*
+ * release a write lock
+ */
+void up_write(struct rw_semaphore *sem)
+{
+	rwsem_release(&sem->dep_map, _RET_IP_);
+	__up_write(sem);
+}
+EXPORT_SYMBOL(up_write);
+
+/*
+ * downgrade write lock to read lock
+ */
+void downgrade_write(struct rw_semaphore *sem)
+{
+	lock_downgrade(&sem->dep_map, _RET_IP_);
+	__downgrade_write(sem);
+}
+EXPORT_SYMBOL(downgrade_write);
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+void down_read_nested(struct rw_semaphore *sem, int subclass)
+{
+	might_sleep();
+	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
+	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
+}
+EXPORT_SYMBOL(down_read_nested);
+
+int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
+{
+	might_sleep();
+	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
+
+	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
+		rwsem_release(&sem->dep_map, _RET_IP_);
+		return -EINTR;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(down_read_killable_nested);
+
+void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
+{
+	might_sleep();
+	rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
+	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
+}
+EXPORT_SYMBOL(_down_write_nest_lock);
+
+void down_read_non_owner(struct rw_semaphore *sem)
+{
+	might_sleep();
+	__down_read(sem);
+	/*
+	 * The owner value for a reader-owned lock is mostly for debugging
+	 * purpose only and is not critical to the correct functioning of
+	 * rwsem. So it is perfectly fine to set it in a preempt-enabled
+	 * context here.
+	 */
+	__rwsem_set_reader_owned(sem, NULL);
+}
+EXPORT_SYMBOL(down_read_non_owner);
+
+void down_write_nested(struct rw_semaphore *sem, int subclass)
+{
+	might_sleep();
+	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
+	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
+}
+EXPORT_SYMBOL(down_write_nested);
+
+int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
+{
+	might_sleep();
+	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
+
+	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
+				  __down_write_killable)) {
+		rwsem_release(&sem->dep_map, _RET_IP_);
+		return -EINTR;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(down_write_killable_nested);
+
+void up_read_non_owner(struct rw_semaphore *sem)
+{
+	DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
+	__up_read(sem);
+}
+EXPORT_SYMBOL(up_read_non_owner);
+
+#endif