locking/rwsem: Merge rwsem.h and rwsem-xadd.c into rwsem.c

Now we only have one implementation of rwsem. Even though we still use
xadd to handle reader locking, we use cmpxchg for writer instead. So
the filename rwsem-xadd.c is not strictly correct. Also no one outside
of the rwsem code need to know the internal implementation other than
function prototypes for two internal functions that are called directly
from percpu-rwsem.c.

So the rwsem-xadd.c and rwsem.h files are now merged into rwsem.c in
the following order:

  <upper part of rwsem.h>
  <rwsem-xadd.c>
  <lower part of rwsem.h>
  <rwsem.c>

The rwsem.h file now contains only 2 function declarations for
__up_read() and __down_read().

This is a code relocation patch with no code change at all except
making __up_read() and __down_read() non-static functions so they
can be used by percpu-rwsem.c.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-5-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 624 deletions

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
deleted file mode 100644
index 7d537b50a849..000000000000
--- a/kernel/locking/rwsem-xadd.c
+++ /dev/null
@@ -1,624 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/* rwsem.c: R/W semaphores: contention handling functions
- *
- * Written by David Howells (dhowells@redhat.com).
- * Derived from arch/i386/kernel/semaphore.c
- *
- * 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 by Waiman Long <longman@redhat.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);
-	sem->owner = NULL;
-#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;
-};
-
-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;
-	struct list_head wlist;
-
-	/*
-	 * 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.
-	 *
-	 * 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.
-	 */
-	list_for_each_entry(waiter, &sem->wait_list, list) {
-		if (waiter->type == RWSEM_WAITING_FOR_WRITE)
-			break;
-
-		woken++;
-	}
-	list_cut_before(&wlist, &sem->wait_list, &waiter->list);
-
-	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);
-
-	/* 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_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);
-	}
-}
-
-/*
- * 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);