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Date:   Thu, 11 Apr 2019 10:37:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH-tip v3 00/14] locking/rwsem: Rwsem rearchitecture part 2



After applying:

 1,2,5,3

Do we want to do something like the below?

There is absolutely no reason anymore we need spread the implementation
over 3 files: rwsem.h rwsem.c rwsem-xadd.c. And I went insane chasing
things around.

Note the below also includes a number of cleanups, there were still a
bunch of EXPORT_SYMBOL()s and __visible crud from back when there was
arch asm.

And I also removed a bunch of pointless wrapper functions.

I suspect there's more cleanups to be had, but for now this will do I
suppose.

---
 a/kernel/locking/rwsem-xadd.c |  608 ------------------------------
 kernel/locking/Makefile       |    2 
 kernel/locking/rwsem.c        |  831 ++++++++++++++++++++++++++++++++++++++++--
 kernel/locking/rwsem.h        |  282 --------------
 4 files changed, 813 insertions(+), 910 deletions(-)

--- a/kernel/locking/Makefile
+++ b/kernel/locking/Makefile
@@ -3,7 +3,7 @@
 # and is generally not a function of system call inputs.
 KCOV_INSTRUMENT		:= n
 
-obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o rwsem-xadd.o
+obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o
 
 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_lockdep.o = $(CC_FLAGS_FTRACE)
--- a/kernel/locking/rwsem-xadd.c
+++ /dev/null
@@ -1,608 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/* rwsem.c: R/W semaphores: contention handling functions
- *
- * Written by David Howells (dhowells@...hat.com).
- * Derived from arch/i386/kernel/semaphore.c
- *
- * Writer lock-stealing by Alex Shi <alex.shi@...el.com>
- * and Michel Lespinasse <walken@...gle.com>
- *
- * Optimistic spinning by Tim Chen <tim.c.chen@...el.com>
- * and Davidlohr Bueso <davidlohr@...com>. Based on mutexes.
- *
- * Rwsem count bit fields re-definition by Waiman Long <longman@...hat.com>.
- */
-#include <linux/rwsem.h>
-#include <linux/init.h>
-#include <linux/export.h>
-#include <linux/sched/signal.h>
-#include <linux/sched/rt.h>
-#include <linux/sched/wake_q.h>
-#include <linux/sched/debug.h>
-#include <linux/osq_lock.h>
-
-#include "rwsem.h"
-
-/*
- * 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(&sem->dep_map, name, key, 0);
-#endif
-	atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
-	raw_spin_lock_init(&sem->wait_lock);
-	INIT_LIST_HEAD(&sem->wait_list);
-#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
-	sem->owner = NULL;
-	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;
-};
-
-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 */
-};
-
-/*
- * 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
- */
-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;
-
-	/*
-	 * Take a peek at the queue head waiter such that we can determine
-	 * the wakeup(s) to perform.
-	 */
-	waiter = list_first_entry(&sem->wait_list, struct rwsem_waiter, list);
-
-	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;
-	}
-
-	/*
-	 * 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) {
-		adjustment = RWSEM_READER_BIAS;
-		oldcount = atomic_long_fetch_add(adjustment, &sem->count);
-		if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
-			atomic_long_sub(adjustment, &sem->count);
-			return;
-		}
-		/*
-		 * Set it to reader-owned to give spinners an early
-		 * indication that readers now have the lock.
-		 */
-		__rwsem_set_reader_owned(sem, waiter->task);
-	}
-
-	/*
-	 * Grant an infinite number of read locks to the readers at the front
-	 * of the queue. We know that 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.
-	 */
-	list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
-		struct task_struct *tsk;
-
-		if (waiter->type == RWSEM_WAITING_FOR_WRITE)
-			break;
-
-		woken++;
-		tsk = waiter->task;
-
-		get_task_struct(tsk);
-		list_del(&waiter->list);
-		/*
-		 * Ensure calling get_task_struct() before setting the reader
-		 * waiter to nil such that rwsem_down_read_failed() 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);
-	}
-
-	adjustment = woken * RWSEM_READER_BIAS - adjustment;
-	lockevent_cond_inc(rwsem_wake_reader, woken);
-	if (list_empty(&sem->wait_list)) {
-		/* hit end of list above */
-		adjustment -= RWSEM_FLAG_WAITERS;
-	}
-
-	if (adjustment)
-		atomic_long_add(adjustment, &sem->count);
-}
-
-/*
- * 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.
- */
-static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
-{
-	long new;
-
-	if (count & RWSEM_LOCK_MASK)
-		return false;
-
-	new = count + RWSEM_WRITER_LOCKED -
-	     (list_is_singular(&sem->wait_list) ? RWSEM_FLAG_WAITERS : 0);
-
-	if (atomic_long_try_cmpxchg_acquire(&sem->count, &count, new)) {
-		rwsem_set_owner(sem);
-		return true;
-	}
-
-	return false;
-}
-
-#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)) {
-		if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
-					count + RWSEM_WRITER_LOCKED)) {
-			rwsem_set_owner(sem);
-			lockevent_inc(rwsem_opt_wlock);
-			return true;
-		}
-	}
-	return false;
-}
-
-static inline bool owner_on_cpu(struct task_struct *owner)
-{
-	/*
-	 * As lock holder preemption issue, we both skip spinning if
-	 * task is not on cpu or its cpu is preempted
-	 */
-	return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
-}
-
-static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
-{
-	struct task_struct *owner;
-	bool ret = true;
-
-	BUILD_BUG_ON(!rwsem_has_anonymous_owner(RWSEM_OWNER_UNKNOWN));
-
-	if (need_resched())
-		return false;
-
-	rcu_read_lock();
-	owner = READ_ONCE(sem->owner);
-	if (owner) {
-		ret = is_rwsem_owner_spinnable(owner) &&
-		      owner_on_cpu(owner);
-	}
-	rcu_read_unlock();
-	return ret;
-}
-
-/*
- * Return true only if we can still spin on the owner field of the rwsem.
- */
-static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
-{
-	struct task_struct *owner = READ_ONCE(sem->owner);
-
-	if (!is_rwsem_owner_spinnable(owner))
-		return false;
-
-	rcu_read_lock();
-	while (owner && (READ_ONCE(sem->owner) == owner)) {
-		/*
-		 * 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,
-		 * the rcu_read_lock() ensures the memory stays valid.
-		 */
-		barrier();
-
-		/*
-		 * abort spinning when need_resched or owner is not running or
-		 * owner's cpu is preempted.
-		 */
-		if (need_resched() || !owner_on_cpu(owner)) {
-			rcu_read_unlock();
-			return false;
-		}
-
-		cpu_relax();
-	}
-	rcu_read_unlock();
-
-	/*
-	 * If there is a new owner or the owner is not set, we continue
-	 * spinning.
-	 */
-	return is_rwsem_owner_spinnable(READ_ONCE(sem->owner));
-}
-
-static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
-{
-	bool taken = false;
-
-	preempt_disable();
-
-	/* sem->wait_lock should not be held when doing optimistic spinning */
-	if (!rwsem_can_spin_on_owner(sem))
-		goto done;
-
-	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 as we can't determine if they are
-	 *     actively running or not.
-	 */
-	while (rwsem_spin_on_owner(sem)) {
-		/*
-		 * Try to acquire the lock
-		 */
-		if (rwsem_try_write_lock_unqueued(sem)) {
-			taken = true;
-			break;
-		}
-
-		/*
-		 * When there's no owner, we might have preempted between the
-		 * owner acquiring the lock and setting the owner field. If
-		 * we're an RT task that will live-lock because we won't let
-		 * the owner complete.
-		 */
-		if (!sem->owner && (need_resched() || rt_task(current)))
-			break;
-
-		/*
-		 * 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:
-	preempt_enable();
-	lockevent_cond_inc(rwsem_opt_fail, !taken);
-	return taken;
-}
-#else
-static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
-{
-	return false;
-}
-#endif
-
-/*
- * Wait for the read lock to be granted
- */
-static inline struct rw_semaphore __sched *
-__rwsem_down_read_failed_common(struct rw_semaphore *sem, int state)
-{
-	long count, adjustment = -RWSEM_READER_BIAS;
-	struct rwsem_waiter waiter;
-	DEFINE_WAKE_Q(wake_q);
-
-	waiter.task = current;
-	waiter.type = RWSEM_WAITING_FOR_READ;
-
-	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)) {
-			raw_spin_unlock_irq(&sem->wait_lock);
-			rwsem_set_reader_owned(sem);
-			lockevent_inc(rwsem_rlock_fast);
-			return sem;
-		}
-		adjustment += RWSEM_FLAG_WAITERS;
-	}
-	list_add_tail(&waiter.list, &sem->wait_list);
-
-	/* we're now waiting on the lock, but no longer actively locking */
-	count = atomic_long_add_return(adjustment, &sem->count);
-
-	/*
-	 * If there are no active locks, wake the front queued process(es).
-	 *
-	 * If there are no writers and we are first in the queue,
-	 * wake our own waiter to join the existing active readers !
-	 */
-	if (!(count & RWSEM_LOCK_MASK) ||
-	   (!(count & RWSEM_WRITER_MASK) && (adjustment & RWSEM_FLAG_WAITERS)))
-		__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
-
-	raw_spin_unlock_irq(&sem->wait_lock);
-	wake_up_q(&wake_q);
-
-	/* wait to be given the lock */
-	while (true) {
-		set_current_state(state);
-		if (!waiter.task)
-			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);
-			break;
-		}
-		schedule();
-		lockevent_inc(rwsem_sleep_reader);
-	}
-
-	__set_current_state(TASK_RUNNING);
-	lockevent_inc(rwsem_rlock);
-	return sem;
-out_nolock:
-	list_del(&waiter.list);
-	if (list_empty(&sem->wait_list))
-		atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count);
-	raw_spin_unlock_irq(&sem->wait_lock);
-	__set_current_state(TASK_RUNNING);
-	lockevent_inc(rwsem_rlock_fail);
-	return ERR_PTR(-EINTR);
-}
-
-__visible struct rw_semaphore * __sched
-rwsem_down_read_failed(struct rw_semaphore *sem)
-{
-	return __rwsem_down_read_failed_common(sem, TASK_UNINTERRUPTIBLE);
-}
-EXPORT_SYMBOL(rwsem_down_read_failed);
-
-__visible struct rw_semaphore * __sched
-rwsem_down_read_failed_killable(struct rw_semaphore *sem)
-{
-	return __rwsem_down_read_failed_common(sem, TASK_KILLABLE);
-}
-EXPORT_SYMBOL(rwsem_down_read_failed_killable);
-
-/*
- * Wait until we successfully acquire the write lock
- */
-static inline struct rw_semaphore *
-__rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
-{
-	long count;
-	bool waiting = true; /* any queued threads before us */
-	struct rwsem_waiter waiter;
-	struct rw_semaphore *ret = sem;
-	DEFINE_WAKE_Q(wake_q);
-
-	/* do optimistic spinning and steal lock if possible */
-	if (rwsem_optimistic_spin(sem))
-		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;
-
-	raw_spin_lock_irq(&sem->wait_lock);
-
-	/* account for this before adding a new element to the list */
-	if (list_empty(&sem->wait_list))
-		waiting = false;
-
-	list_add_tail(&waiter.list, &sem->wait_list);
-
-	/* we're now waiting on the lock */
-	if (waiting) {
-		count = atomic_long_read(&sem->count);
-
-		/*
-		 * If there were already threads queued before us and there are
-		 * no active writers and some readers, the lock must be read
-		 * owned; so we try to  any read locks that were queued ahead
-		 * of us.
-		 */
-		if (!(count & RWSEM_WRITER_MASK) &&
-		     (count & RWSEM_READER_MASK)) {
-			__rwsem_mark_wake(sem, RWSEM_WAKE_READERS, &wake_q);
-			/*
-			 * The wakeup is normally called _after_ the wait_lock
-			 * is released, but given that we are proactively waking
-			 * readers we can deal with the wake_q overhead as it is
-			 * similar to releasing and taking the wait_lock again
-			 * for attempting rwsem_try_write_lock().
-			 */
-			wake_up_q(&wake_q);
-
-			/*
-			 * Reinitialize wake_q after use.
-			 */
-			wake_q_init(&wake_q);
-		}
-
-	} else {
-		count = atomic_long_add_return(RWSEM_FLAG_WAITERS, &sem->count);
-	}
-
-	/* wait until we successfully acquire the lock */
-	set_current_state(state);
-	while (true) {
-		if (rwsem_try_write_lock(count, sem))
-			break;
-		raw_spin_unlock_irq(&sem->wait_lock);
-
-		/* Block until there are no active lockers. */
-		do {
-			if (signal_pending_state(state, current))
-				goto out_nolock;
-
-			schedule();
-			lockevent_inc(rwsem_sleep_writer);
-			set_current_state(state);
-			count = atomic_long_read(&sem->count);
-		} while (count & RWSEM_LOCK_MASK);
-
-		raw_spin_lock_irq(&sem->wait_lock);
-	}
-	__set_current_state(TASK_RUNNING);
-	list_del(&waiter.list);
-	raw_spin_unlock_irq(&sem->wait_lock);
-	lockevent_inc(rwsem_wlock);
-
-	return ret;
-
-out_nolock:
-	__set_current_state(TASK_RUNNING);
-	raw_spin_lock_irq(&sem->wait_lock);
-	list_del(&waiter.list);
-	if (list_empty(&sem->wait_list))
-		atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count);
-	else
-		__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
-	raw_spin_unlock_irq(&sem->wait_lock);
-	wake_up_q(&wake_q);
-	lockevent_inc(rwsem_wlock_fail);
-
-	return ERR_PTR(-EINTR);
-}
-
-__visible struct rw_semaphore * __sched
-rwsem_down_write_failed(struct rw_semaphore *sem)
-{
-	return __rwsem_down_write_failed_common(sem, TASK_UNINTERRUPTIBLE);
-}
-EXPORT_SYMBOL(rwsem_down_write_failed);
-
-__visible struct rw_semaphore * __sched
-rwsem_down_write_failed_killable(struct rw_semaphore *sem)
-{
-	return __rwsem_down_write_failed_common(sem, TASK_KILLABLE);
-}
-EXPORT_SYMBOL(rwsem_down_write_failed_killable);
-
-/*
- * handle waking up a waiter on the semaphore
- * - up_read/up_write has decremented the active part of count if we come here
- */
-__visible
-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;
-}
-EXPORT_SYMBOL(rwsem_wake);
-
-/*
- * 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
- */
-__visible
-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;
-}
-EXPORT_SYMBOL(rwsem_downgrade_wake);
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -8,12 +8,811 @@
 #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/export.h>
 #include <linux/rwsem.h>
 #include <linux/atomic.h>
 
-#include "rwsem.h"
+/*
+ * The least significant 2 bits of the owner value has the following
+ * meanings when set.
+ *  - RWSEM_READER_OWNED (bit 0): The rwsem is owned by readers
+ *  - RWSEM_ANONYMOUSLY_OWNED (bit 1): The rwsem is anonymously owned,
+ *    i.e. the owner(s) cannot be readily determined. It can be reader
+ *    owned or the owning writer is indeterminate.
+ *
+ * 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 both the RWSEM_READER_OWNED and
+ * RWSEM_ANONYMOUSLY_OWNED bits 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. The anonymous bit is set because that particular
+ * reader may or may not still own the lock.
+ *
+ * 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.
+ */
+#include "lock_events.h"
+
+#define RWSEM_READER_OWNED	(1UL << 0)
+#define RWSEM_ANONYMOUSLY_OWNED	(1UL << 1)
+
+#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, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
+		#c, atomic_long_read(&(sem)->count),		\
+		(long)((sem)->owner), (long)current,		\
+		list_empty(&(sem)->wait_list) ? "" : "not "))	\
+			debug_locks_off();			\
+	} while (0)
+#else
+# define DEBUG_RWSEMS_WARN_ON(c, sem)
+#endif
+
+/*
+ * The definition of the atomic counter in the semaphore:
+ *
+ * Bit  0   - writer locked bit
+ * Bit  1   - waiters present bit
+ * Bits 2-7 - reserved
+ * Bits 8-X - 24-bit (32-bit) or 56-bit reader count
+ *
+ * atomic_long_fetch_add() is used to obtain reader lock, whereas
+ * atomic_long_cmpxchg() will be used to obtain writer lock.
+ */
+#define RWSEM_WRITER_LOCKED	(1UL << 0)
+#define RWSEM_FLAG_WAITERS	(1UL << 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)
+
+
+/*
+ * 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.
+ */
+static inline void rwsem_set_owner(struct rw_semaphore *sem)
+{
+	WRITE_ONCE(sem->owner, current);
+}
+
+static inline void rwsem_clear_owner(struct rw_semaphore *sem)
+{
+	WRITE_ONCE(sem->owner, NULL);
+}
+
+/*
+ * 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.
+ */
+static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
+					    struct task_struct *owner)
+{
+	unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED
+						 | RWSEM_ANONYMOUSLY_OWNED;
+
+	WRITE_ONCE(sem->owner, (struct task_struct *)val);
+}
+
+static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
+{
+	__rwsem_set_reader_owned(sem, current);
+}
+
+/*
+ * Return true if the a rwsem waiter can spin on the rwsem's owner
+ * and steal the lock, i.e. the lock is not anonymously owned.
+ * N.B. !owner is considered spinnable.
+ */
+static inline bool is_rwsem_owner_spinnable(struct task_struct *owner)
+{
+	return !((unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED);
+}
+
+/*
+ * Return true if rwsem is owned by an anonymous writer or readers.
+ */
+static inline bool rwsem_has_anonymous_owner(struct task_struct *owner)
+{
+	return (unsigned long)owner & RWSEM_ANONYMOUSLY_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 = (unsigned long)current | RWSEM_READER_OWNED
+						   | RWSEM_ANONYMOUSLY_OWNED;
+	if (READ_ONCE(sem->owner) == (struct task_struct *)val)
+		cmpxchg_relaxed((unsigned long *)&sem->owner, val,
+				RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED);
+}
+#else
+static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
+{
+}
+#endif
+
+/*
+ * 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(&sem->dep_map, name, key, 0);
+#endif
+	atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
+	raw_spin_lock_init(&sem->wait_lock);
+	INIT_LIST_HEAD(&sem->wait_list);
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
+	sem->owner = NULL;
+	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;
+};
+
+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 */
+};
+
+/*
+ * 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
+ */
+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;
+
+	/*
+	 * Take a peek at the queue head waiter such that we can determine
+	 * the wakeup(s) to perform.
+	 */
+	waiter = list_first_entry(&sem->wait_list, struct rwsem_waiter, list);
+
+	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;
+	}
+
+	/*
+	 * 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) {
+		adjustment = RWSEM_READER_BIAS;
+		oldcount = atomic_long_fetch_add(adjustment, &sem->count);
+		if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
+			atomic_long_sub(adjustment, &sem->count);
+			return;
+		}
+		/*
+		 * Set it to reader-owned to give spinners an early
+		 * indication that readers now have the lock.
+		 */
+		__rwsem_set_reader_owned(sem, waiter->task);
+	}
+
+	/*
+	 * Grant an infinite number of read locks to the readers at the front
+	 * of the queue. We know that 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.
+	 */
+	list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
+		struct task_struct *tsk;
+
+		if (waiter->type == RWSEM_WAITING_FOR_WRITE)
+			break;
+
+		woken++;
+		tsk = waiter->task;
+
+		get_task_struct(tsk);
+		list_del(&waiter->list);
+		/*
+		 * Ensure calling get_task_struct() before setting the reader
+		 * waiter to nil such that rwsem_down_read_failed()
+		 * 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);
+	}
+
+	adjustment = woken * RWSEM_READER_BIAS - adjustment;
+	lockevent_cond_inc(rwsem_wake_reader, woken);
+	if (list_empty(&sem->wait_list)) {
+		/* hit end of list above */
+		adjustment -= RWSEM_FLAG_WAITERS;
+	}
+
+	if (adjustment)
+		atomic_long_add(adjustment, &sem->count);
+}
+
+/*
+ * 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.
+ */
+static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
+{
+	long new;
+
+	if (count & RWSEM_LOCK_MASK)
+		return false;
+
+	new = count + RWSEM_WRITER_LOCKED -
+	     (list_is_singular(&sem->wait_list) ? RWSEM_FLAG_WAITERS : 0);
+
+	if (atomic_long_try_cmpxchg_acquire(&sem->count, &count, new)) {
+		rwsem_set_owner(sem);
+		return true;
+	}
+
+	return false;
+}
+
+#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)) {
+		if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
+					count + RWSEM_WRITER_LOCKED)) {
+			rwsem_set_owner(sem);
+			lockevent_inc(rwsem_opt_wlock);
+			return true;
+		}
+	}
+	return false;
+}
+
+static inline bool owner_on_cpu(struct task_struct *owner)
+{
+	/*
+	 * As lock holder preemption issue, we both skip spinning if
+	 * task is not on cpu or its cpu is preempted
+	 */
+	return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
+}
+
+static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
+{
+	struct task_struct *owner;
+	bool ret = true;
+
+	BUILD_BUG_ON(!rwsem_has_anonymous_owner(RWSEM_OWNER_UNKNOWN));
+
+	if (need_resched())
+		return false;
+
+	rcu_read_lock();
+	owner = READ_ONCE(sem->owner);
+	if (owner) {
+		ret = is_rwsem_owner_spinnable(owner) &&
+		      owner_on_cpu(owner);
+	}
+	rcu_read_unlock();
+	return ret;
+}
+
+/*
+ * Return true only if we can still spin on the owner field of the rwsem.
+ */
+static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
+{
+	struct task_struct *owner = READ_ONCE(sem->owner);
+
+	if (!is_rwsem_owner_spinnable(owner))
+		return false;
+
+	rcu_read_lock();
+	while (owner && (READ_ONCE(sem->owner) == owner)) {
+		/*
+		 * 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,
+		 * the rcu_read_lock() ensures the memory stays valid.
+		 */
+		barrier();
+
+		/*
+		 * abort spinning when need_resched or owner is not running or
+		 * owner's cpu is preempted.
+		 */
+		if (need_resched() || !owner_on_cpu(owner)) {
+			rcu_read_unlock();
+			return false;
+		}
+
+		cpu_relax();
+	}
+	rcu_read_unlock();
+
+	/*
+	 * If there is a new owner or the owner is not set, we continue
+	 * spinning.
+	 */
+	return is_rwsem_owner_spinnable(READ_ONCE(sem->owner));
+}
+
+static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
+{
+	bool taken = false;
+
+	preempt_disable();
+
+	/* sem->wait_lock should not be held when doing optimistic spinning */
+	if (!rwsem_can_spin_on_owner(sem))
+		goto done;
+
+	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 as we can't determine if they are
+	 *     actively running or not.
+	 */
+	while (rwsem_spin_on_owner(sem)) {
+		/*
+		 * Try to acquire the lock
+		 */
+		if (rwsem_try_write_lock_unqueued(sem)) {
+			taken = true;
+			break;
+		}
+
+		/*
+		 * When there's no owner, we might have preempted between the
+		 * owner acquiring the lock and setting the owner field. If
+		 * we're an RT task that will live-lock because we won't let
+		 * the owner complete.
+		 */
+		if (!sem->owner && (need_resched() || rt_task(current)))
+			break;
+
+		/*
+		 * 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:
+	preempt_enable();
+	lockevent_cond_inc(rwsem_opt_fail, !taken);
+	return taken;
+}
+#else
+static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
+{
+	return false;
+}
+#endif
+
+/*
+ * Wait for the read lock to be granted
+ */
+static inline struct rw_semaphore __sched *
+rwsem_down_read_failed(struct rw_semaphore *sem, int state)
+{
+	long count, adjustment = -RWSEM_READER_BIAS;
+	struct rwsem_waiter waiter;
+	DEFINE_WAKE_Q(wake_q);
+
+	waiter.task = current;
+	waiter.type = RWSEM_WAITING_FOR_READ;
+
+	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)) {
+			raw_spin_unlock_irq(&sem->wait_lock);
+			rwsem_set_reader_owned(sem);
+			lockevent_inc(rwsem_rlock_fast);
+			return sem;
+		}
+		adjustment += RWSEM_FLAG_WAITERS;
+	}
+	list_add_tail(&waiter.list, &sem->wait_list);
+
+	/* we're now waiting on the lock, but no longer actively locking */
+	count = atomic_long_add_return(adjustment, &sem->count);
+
+	/*
+	 * If there are no active locks, wake the front queued process(es).
+	 *
+	 * If there are no writers and we are first in the queue,
+	 * wake our own waiter to join the existing active readers !
+	 */
+	if (!(count & RWSEM_LOCK_MASK) ||
+	   (!(count & RWSEM_WRITER_MASK) && (adjustment & RWSEM_FLAG_WAITERS)))
+		__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
+
+	raw_spin_unlock_irq(&sem->wait_lock);
+	wake_up_q(&wake_q);
+
+	/* wait to be given the lock */
+	while (true) {
+		set_current_state(state);
+		if (!waiter.task)
+			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);
+			break;
+		}
+		schedule();
+		lockevent_inc(rwsem_sleep_reader);
+	}
+
+	__set_current_state(TASK_RUNNING);
+	lockevent_inc(rwsem_rlock);
+	return sem;
+out_nolock:
+	list_del(&waiter.list);
+	if (list_empty(&sem->wait_list))
+		atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count);
+	raw_spin_unlock_irq(&sem->wait_lock);
+	__set_current_state(TASK_RUNNING);
+	lockevent_inc(rwsem_rlock_fail);
+	return ERR_PTR(-EINTR);
+}
+
+/*
+ * Wait until we successfully acquire the write lock
+ */
+static inline struct rw_semaphore *
+rwsem_down_write_failed(struct rw_semaphore *sem, int state)
+{
+	long count;
+	bool waiting = true; /* any queued threads before us */
+	struct rwsem_waiter waiter;
+	struct rw_semaphore *ret = sem;
+	DEFINE_WAKE_Q(wake_q);
+
+	/* do optimistic spinning and steal lock if possible */
+	if (rwsem_optimistic_spin(sem))
+		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;
+
+	raw_spin_lock_irq(&sem->wait_lock);
+
+	/* account for this before adding a new element to the list */
+	if (list_empty(&sem->wait_list))
+		waiting = false;
+
+	list_add_tail(&waiter.list, &sem->wait_list);
+
+	/* we're now waiting on the lock */
+	if (waiting) {
+		count = atomic_long_read(&sem->count);
+
+		/*
+		 * If there were already threads queued before us and there are
+		 * no active writers and some readers, the lock must be read
+		 * owned; so we try to  any read locks that were queued ahead
+		 * of us.
+		 */
+		if (!(count & RWSEM_WRITER_MASK) &&
+		     (count & RWSEM_READER_MASK)) {
+			__rwsem_mark_wake(sem, RWSEM_WAKE_READERS, &wake_q);
+			/*
+			 * The wakeup is normally called _after_ the wait_lock
+			 * is released, but given that we are proactively waking
+			 * readers we can deal with the wake_q overhead as it is
+			 * similar to releasing and taking the wait_lock again
+			 * for attempting rwsem_try_write_lock().
+			 */
+			wake_up_q(&wake_q);
+
+			/*
+			 * Reinitialize wake_q after use.
+			 */
+			wake_q_init(&wake_q);
+		}
+
+	} else {
+		count = atomic_long_add_return(RWSEM_FLAG_WAITERS, &sem->count);
+	}
+
+	/* wait until we successfully acquire the lock */
+	set_current_state(state);
+	while (true) {
+		if (rwsem_try_write_lock(count, sem))
+			break;
+		raw_spin_unlock_irq(&sem->wait_lock);
+
+		/* Block until there are no active lockers. */
+		do {
+			if (signal_pending_state(state, current))
+				goto out_nolock;
+
+			schedule();
+			lockevent_inc(rwsem_sleep_writer);
+			set_current_state(state);
+			count = atomic_long_read(&sem->count);
+		} while (count & RWSEM_LOCK_MASK);
+
+		raw_spin_lock_irq(&sem->wait_lock);
+	}
+	__set_current_state(TASK_RUNNING);
+	list_del(&waiter.list);
+	raw_spin_unlock_irq(&sem->wait_lock);
+	lockevent_inc(rwsem_wlock);
+
+	return ret;
+
+out_nolock:
+	__set_current_state(TASK_RUNNING);
+	raw_spin_lock_irq(&sem->wait_lock);
+	list_del(&waiter.list);
+	if (list_empty(&sem->wait_list))
+		atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count);
+	else
+		__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
+	raw_spin_unlock_irq(&sem->wait_lock);
+	wake_up_q(&wake_q);
+	lockevent_inc(rwsem_wlock_fail);
+
+	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;
+}
+
+/*
+ * lock for reading
+ */
+inline void __down_read(struct rw_semaphore *sem)
+{
+	if (unlikely(atomic_long_fetch_add_acquire(RWSEM_READER_BIAS,
+			&sem->count) & RWSEM_READ_FAILED_MASK)) {
+		rwsem_down_read_failed(sem, TASK_UNINTERRUPTIBLE);
+		DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner &
+					RWSEM_READER_OWNED), sem);
+	} else {
+		rwsem_set_reader_owned(sem);
+	}
+}
+
+static inline int __down_read_killable(struct rw_semaphore *sem)
+{
+	if (unlikely(atomic_long_fetch_add_acquire(RWSEM_READER_BIAS,
+			&sem->count) & RWSEM_READ_FAILED_MASK)) {
+		if (IS_ERR(rwsem_down_read_failed(sem, TASK_KILLABLE)))
+			return -EINTR;
+		DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner &
+					RWSEM_READER_OWNED), sem);
+	} else {
+		rwsem_set_reader_owned(sem);
+	}
+	return 0;
+}
+
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+	/*
+	 * Optimize for the case when the rwsem is not locked at all.
+	 */
+	long tmp = RWSEM_UNLOCKED_VALUE;
+
+	lockevent_inc(rwsem_rtrylock);
+	do {
+		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
+					tmp + RWSEM_READER_BIAS)) {
+			rwsem_set_reader_owned(sem);
+			return 1;
+		}
+	} while (!(tmp & RWSEM_READ_FAILED_MASK));
+	return 0;
+}
+
+/*
+ * lock for writing
+ */
+static inline void __down_write(struct rw_semaphore *sem)
+{
+	if (unlikely(atomic_long_cmpxchg_acquire(&sem->count, 0,
+						 RWSEM_WRITER_LOCKED)))
+		rwsem_down_write_failed(sem, TASK_UNINTERRUPTIBLE);
+	rwsem_set_owner(sem);
+}
+
+static inline int __down_write_killable(struct rw_semaphore *sem)
+{
+	if (unlikely(atomic_long_cmpxchg_acquire(&sem->count, 0,
+						 RWSEM_WRITER_LOCKED))) {
+		if (IS_ERR(rwsem_down_write_failed(sem, TASK_KILLABLE)))
+			return -EINTR;
+	}
+	rwsem_set_owner(sem);
+	return 0;
+}
+
+static inline int __down_write_trylock(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	lockevent_inc(rwsem_wtrylock);
+	tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
+					  RWSEM_WRITER_LOCKED);
+	if (tmp == RWSEM_UNLOCKED_VALUE) {
+		rwsem_set_owner(sem);
+		return true;
+	}
+	return false;
+}
+
+/*
+ * unlock after reading
+ */
+inline void __up_read(struct rw_semaphore *sem)
+{
+	long tmp;
+
+	DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED),
+				sem);
+	rwsem_clear_reader_owned(sem);
+	tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
+	if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) == RWSEM_FLAG_WAITERS))
+		rwsem_wake(sem);
+}
+
+/*
+ * unlock after writing
+ */
+static inline void __up_write(struct rw_semaphore *sem)
+{
+	DEBUG_RWSEMS_WARN_ON(sem->owner != current, sem);
+	rwsem_clear_owner(sem);
+	if (unlikely(atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED,
+			&sem->count) & RWSEM_FLAG_WAITERS))
+		rwsem_wake(sem);
+}
+
+/*
+ * 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(sem->owner != current, sem);
+	tmp = atomic_long_fetch_add_release(
+		-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
+	rwsem_set_reader_owned(sem);
+
+	if (tmp & RWSEM_FLAG_WAITERS) {
+		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);
+	}
+}
 
 /*
  * lock for reading
@@ -25,7 +824,6 @@ void __sched down_read(struct rw_semapho
 
 	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 }
-
 EXPORT_SYMBOL(down_read);
 
 int __sched down_read_killable(struct rw_semaphore *sem)
@@ -40,7 +838,6 @@ int __sched down_read_killable(struct rw
 
 	return 0;
 }
-
 EXPORT_SYMBOL(down_read_killable);
 
 /*
@@ -54,7 +851,6 @@ int down_read_trylock(struct rw_semaphor
 		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
 	return ret;
 }
-
 EXPORT_SYMBOL(down_read_trylock);
 
 /*
@@ -64,10 +860,8 @@ void __sched down_write(struct rw_semaph
 {
 	might_sleep();
 	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
-
 	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 }
-
 EXPORT_SYMBOL(down_write);
 
 /*
@@ -85,7 +879,6 @@ int __sched down_write_killable(struct r
 
 	return 0;
 }
-
 EXPORT_SYMBOL(down_write_killable);
 
 /*
@@ -100,7 +893,6 @@ int down_write_trylock(struct rw_semapho
 
 	return ret;
 }
-
 EXPORT_SYMBOL(down_write_trylock);
 
 /*
@@ -109,10 +901,8 @@ EXPORT_SYMBOL(down_write_trylock);
 void up_read(struct rw_semaphore *sem)
 {
 	rwsem_release(&sem->dep_map, 1, _RET_IP_);
-
 	__up_read(sem);
 }
-
 EXPORT_SYMBOL(up_read);
 
 /*
@@ -121,10 +911,8 @@ EXPORT_SYMBOL(up_read);
 void up_write(struct rw_semaphore *sem)
 {
 	rwsem_release(&sem->dep_map, 1, _RET_IP_);
-
 	__up_write(sem);
 }
-
 EXPORT_SYMBOL(up_write);
 
 /*
@@ -133,45 +921,40 @@ EXPORT_SYMBOL(up_write);
 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)
+void __sched down_read_nested(struct rw_semaphore *sem, int subclass)
 {
 	might_sleep();
-	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 
+	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 }
-
 EXPORT_SYMBOL(down_read_nested);
 
-void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
+void __sched _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_);
 
+	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)
+void __sched down_read_non_owner(struct rw_semaphore *sem)
 {
 	might_sleep();
 
 	__down_read(sem);
 	__rwsem_set_reader_owned(sem, NULL);
 }
-
 EXPORT_SYMBOL(down_read_non_owner);
 
-void down_write_nested(struct rw_semaphore *sem, int subclass)
+void __sched down_write_nested(struct rw_semaphore *sem, int subclass)
 {
 	might_sleep();
 	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
@@ -193,7 +976,6 @@ int __sched down_write_killable_nested(s
 
 	return 0;
 }
-
 EXPORT_SYMBOL(down_write_killable_nested);
 
 void up_read_non_owner(struct rw_semaphore *sem)
@@ -202,7 +984,6 @@ void up_read_non_owner(struct rw_semapho
 				sem);
 	__up_read(sem);
 }
-
 EXPORT_SYMBOL(up_read_non_owner);
 
 #endif
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -1,280 +1,10 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-/*
- * The least significant 2 bits of the owner value has the following
- * meanings when set.
- *  - RWSEM_READER_OWNED (bit 0): The rwsem is owned by readers
- *  - RWSEM_ANONYMOUSLY_OWNED (bit 1): The rwsem is anonymously owned,
- *    i.e. the owner(s) cannot be readily determined. It can be reader
- *    owned or the owning writer is indeterminate.
- *
- * 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 both the RWSEM_READER_OWNED and
- * RWSEM_ANONYMOUSLY_OWNED bits 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. The anonymous bit is set because that particular
- * reader may or may not still own the lock.
- *
- * 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.
- */
-#include "lock_events.h"
+#ifndef __INTERNAL_RWSEM_H
+#define __INTERNAL_RWSEM_H
 
-#define RWSEM_READER_OWNED	(1UL << 0)
-#define RWSEM_ANONYMOUSLY_OWNED	(1UL << 1)
+#include <linux/rwsem.h>
 
-#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, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
-		#c, atomic_long_read(&(sem)->count),		\
-		(long)((sem)->owner), (long)current,		\
-		list_empty(&(sem)->wait_list) ? "" : "not "))	\
-			debug_locks_off();			\
-	} while (0)
-#else
-# define DEBUG_RWSEMS_WARN_ON(c, sem)
-#endif
+extern void __down_read(struct rw_semaphore *sem);
+extern void __up_read(struct rw_semaphore *sem);
 
-/*
- * The definition of the atomic counter in the semaphore:
- *
- * Bit  0   - writer locked bit
- * Bit  1   - waiters present bit
- * Bits 2-7 - reserved
- * Bits 8-X - 24-bit (32-bit) or 56-bit reader count
- *
- * atomic_long_fetch_add() is used to obtain reader lock, whereas
- * atomic_long_cmpxchg() will be used to obtain writer lock.
- */
-#define RWSEM_WRITER_LOCKED	(1UL << 0)
-#define RWSEM_FLAG_WAITERS	(1UL << 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)
-
-
-/*
- * 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.
- */
-static inline void rwsem_set_owner(struct rw_semaphore *sem)
-{
-	WRITE_ONCE(sem->owner, current);
-}
-
-static inline void rwsem_clear_owner(struct rw_semaphore *sem)
-{
-	WRITE_ONCE(sem->owner, NULL);
-}
-
-/*
- * 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.
- */
-static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
-					    struct task_struct *owner)
-{
-	unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED
-						 | RWSEM_ANONYMOUSLY_OWNED;
-
-	WRITE_ONCE(sem->owner, (struct task_struct *)val);
-}
-
-static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
-{
-	__rwsem_set_reader_owned(sem, current);
-}
-
-/*
- * Return true if the a rwsem waiter can spin on the rwsem's owner
- * and steal the lock, i.e. the lock is not anonymously owned.
- * N.B. !owner is considered spinnable.
- */
-static inline bool is_rwsem_owner_spinnable(struct task_struct *owner)
-{
-	return !((unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED);
-}
-
-/*
- * Return true if rwsem is owned by an anonymous writer or readers.
- */
-static inline bool rwsem_has_anonymous_owner(struct task_struct *owner)
-{
-	return (unsigned long)owner & RWSEM_ANONYMOUSLY_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 = (unsigned long)current | RWSEM_READER_OWNED
-						   | RWSEM_ANONYMOUSLY_OWNED;
-	if (READ_ONCE(sem->owner) == (struct task_struct *)val)
-		cmpxchg_relaxed((unsigned long *)&sem->owner, val,
-				RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED);
-}
-#else
-static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
-{
-}
-#endif
-
-extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
-extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem);
-extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
-extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
-extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
-extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
-
-/*
- * lock for reading
- */
-static inline void __down_read(struct rw_semaphore *sem)
-{
-	if (unlikely(atomic_long_fetch_add_acquire(RWSEM_READER_BIAS,
-			&sem->count) & RWSEM_READ_FAILED_MASK)) {
-		rwsem_down_read_failed(sem);
-		DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner &
-					RWSEM_READER_OWNED), sem);
-	} else {
-		rwsem_set_reader_owned(sem);
-	}
-}
-
-static inline int __down_read_killable(struct rw_semaphore *sem)
-{
-	if (unlikely(atomic_long_fetch_add_acquire(RWSEM_READER_BIAS,
-			&sem->count) & RWSEM_READ_FAILED_MASK)) {
-		if (IS_ERR(rwsem_down_read_failed_killable(sem)))
-			return -EINTR;
-		DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner &
-					RWSEM_READER_OWNED), sem);
-	} else {
-		rwsem_set_reader_owned(sem);
-	}
-	return 0;
-}
-
-static inline int __down_read_trylock(struct rw_semaphore *sem)
-{
-	/*
-	 * Optimize for the case when the rwsem is not locked at all.
-	 */
-	long tmp = RWSEM_UNLOCKED_VALUE;
-
-	lockevent_inc(rwsem_rtrylock);
-	do {
-		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
-					tmp + RWSEM_READER_BIAS)) {
-			rwsem_set_reader_owned(sem);
-			return 1;
-		}
-	} while (!(tmp & RWSEM_READ_FAILED_MASK));
-	return 0;
-}
-
-/*
- * lock for writing
- */
-static inline void __down_write(struct rw_semaphore *sem)
-{
-	if (unlikely(atomic_long_cmpxchg_acquire(&sem->count, 0,
-						 RWSEM_WRITER_LOCKED)))
-		rwsem_down_write_failed(sem);
-	rwsem_set_owner(sem);
-}
-
-static inline int __down_write_killable(struct rw_semaphore *sem)
-{
-	if (unlikely(atomic_long_cmpxchg_acquire(&sem->count, 0,
-						 RWSEM_WRITER_LOCKED)))
-		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
-			return -EINTR;
-	rwsem_set_owner(sem);
-	return 0;
-}
-
-static inline int __down_write_trylock(struct rw_semaphore *sem)
-{
-	long tmp;
-
-	lockevent_inc(rwsem_wtrylock);
-	tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
-					  RWSEM_WRITER_LOCKED);
-	if (tmp == RWSEM_UNLOCKED_VALUE) {
-		rwsem_set_owner(sem);
-		return true;
-	}
-	return false;
-}
-
-/*
- * unlock after reading
- */
-static inline void __up_read(struct rw_semaphore *sem)
-{
-	long tmp;
-
-	DEBUG_RWSEMS_WARN_ON(!((unsigned long)sem->owner & RWSEM_READER_OWNED),
-				sem);
-	rwsem_clear_reader_owned(sem);
-	tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
-	if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS))
-			== RWSEM_FLAG_WAITERS))
-		rwsem_wake(sem);
-}
-
-/*
- * unlock after writing
- */
-static inline void __up_write(struct rw_semaphore *sem)
-{
-	DEBUG_RWSEMS_WARN_ON(sem->owner != current, sem);
-	rwsem_clear_owner(sem);
-	if (unlikely(atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED,
-			&sem->count) & RWSEM_FLAG_WAITERS))
-		rwsem_wake(sem);
-}
-
-/*
- * 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(sem->owner != current, sem);
-	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);
-}
+#endif /* __INTERNAL_RWSEM_H */

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