fs/btrfs/locking.c - kernel/msm-4.9 - Gitiles

 /*
  * Copyright (C) 2008 Oracle.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public
  * License v2 as published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
  *
  * You should have received a copy of the GNU General Public
  * License along with this program; if not, write to the
  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  * Boston, MA 021110-1307, USA.
  */
 #include <linux/sched.h>
 #include <linux/pagemap.h>
 #include <linux/spinlock.h>
 #include <linux/page-flags.h>
 #include <asm/bug.h>
 #include "ctree.h"
 #include "extent_io.h"
 #include "locking.h"

 static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);

 /*
  * if we currently have a spinning reader or writer lock
  * (indicated by the rw flag) this will bump the count
  * of blocking holders and drop the spinlock.
  */
 void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
 {
 	/*
 	 * no lock is required.  The lock owner may change if
 	 * we have a read lock, but it won't change to or away
 	 * from us.  If we have the write lock, we are the owner
 	 * and it'll never change.
 	 */
 	if (eb->lock_nested && current->pid == eb->lock_owner)
 		return;
 	if (rw == BTRFS_WRITE_LOCK) {
 		if (atomic_read(&eb->blocking_writers) == 0) {
 			WARN_ON(atomic_read(&eb->spinning_writers) != 1);
 			atomic_dec(&eb->spinning_writers);
 			btrfs_assert_tree_locked(eb);
 			atomic_inc(&eb->blocking_writers);
 			write_unlock(&eb->lock);
 		}
 	} else if (rw == BTRFS_READ_LOCK) {
 		btrfs_assert_tree_read_locked(eb);
 		atomic_inc(&eb->blocking_readers);
 		WARN_ON(atomic_read(&eb->spinning_readers) == 0);
 		atomic_dec(&eb->spinning_readers);
 		read_unlock(&eb->lock);
 	}
 }

 /*
  * if we currently have a blocking lock, take the spinlock
  * and drop our blocking count
  */
 void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
 {
 	/*
 	 * no lock is required.  The lock owner may change if
 	 * we have a read lock, but it won't change to or away
 	 * from us.  If we have the write lock, we are the owner
 	 * and it'll never change.
 	 */
 	if (eb->lock_nested && current->pid == eb->lock_owner)
 		return;

 	if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
 		BUG_ON(atomic_read(&eb->blocking_writers) != 1);
 		write_lock(&eb->lock);
 		WARN_ON(atomic_read(&eb->spinning_writers));
 		atomic_inc(&eb->spinning_writers);
 		/*
 		 * atomic_dec_and_test implies a barrier for waitqueue_active
 		 */
 		if (atomic_dec_and_test(&eb->blocking_writers) &&
 		    waitqueue_active(&eb->write_lock_wq))
 			wake_up(&eb->write_lock_wq);
 	} else if (rw == BTRFS_READ_LOCK_BLOCKING) {
 		BUG_ON(atomic_read(&eb->blocking_readers) == 0);
 		read_lock(&eb->lock);
 		atomic_inc(&eb->spinning_readers);
 		/*
 		 * atomic_dec_and_test implies a barrier for waitqueue_active
 		 */
 		if (atomic_dec_and_test(&eb->blocking_readers) &&
 		    waitqueue_active(&eb->read_lock_wq))
 			wake_up(&eb->read_lock_wq);
 	}
 }

 /*
  * take a spinning read lock.  This will wait for any blocking
  * writers
  */
 void btrfs_tree_read_lock(struct extent_buffer *eb)
 {
 again:
 	BUG_ON(!atomic_read(&eb->blocking_writers) &&
 	       current->pid == eb->lock_owner);

 	read_lock(&eb->lock);
 	if (atomic_read(&eb->blocking_writers) &&
 	    current->pid == eb->lock_owner) {
 		/*
 		 * This extent is already write-locked by our thread. We allow
 		 * an additional read lock to be added because it's for the same
 		 * thread. btrfs_find_all_roots() depends on this as it may be
 		 * called on a partly (write-)locked tree.
 		 */
 		BUG_ON(eb->lock_nested);
 		eb->lock_nested = 1;
 		read_unlock(&eb->lock);
 		return;
 	}
 	if (atomic_read(&eb->blocking_writers)) {
 		read_unlock(&eb->lock);
 		wait_event(eb->write_lock_wq,
 			   atomic_read(&eb->blocking_writers) == 0);
 		goto again;
 	}
 	atomic_inc(&eb->read_locks);
 	atomic_inc(&eb->spinning_readers);
 }

 /*
  * take a spinning read lock.
  * returns 1 if we get the read lock and 0 if we don't
  * this won't wait for blocking writers
  */
 int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
 {
 	if (atomic_read(&eb->blocking_writers))
 		return 0;

 	read_lock(&eb->lock);
 	if (atomic_read(&eb->blocking_writers)) {
 		read_unlock(&eb->lock);
 		return 0;
 	}
 	atomic_inc(&eb->read_locks);
 	atomic_inc(&eb->spinning_readers);
 	return 1;
 }

 /*
  * returns 1 if we get the read lock and 0 if we don't
  * this won't wait for blocking writers
  */
 int btrfs_try_tree_read_lock(struct extent_buffer *eb)
 {
 	if (atomic_read(&eb->blocking_writers))
 		return 0;

 	if (!read_trylock(&eb->lock))
 		return 0;

 	if (atomic_read(&eb->blocking_writers)) {
 		read_unlock(&eb->lock);
 		return 0;
 	}
 	atomic_inc(&eb->read_locks);
 	atomic_inc(&eb->spinning_readers);
 	return 1;
 }

 /*
  * returns 1 if we get the read lock and 0 if we don't
  * this won't wait for blocking writers or readers
  */
 int btrfs_try_tree_write_lock(struct extent_buffer *eb)
 {
 	if (atomic_read(&eb->blocking_writers) ||
 	    atomic_read(&eb->blocking_readers))
 		return 0;

 	write_lock(&eb->lock);
 	if (atomic_read(&eb->blocking_writers) ||
 	    atomic_read(&eb->blocking_readers)) {
 		write_unlock(&eb->lock);
 		return 0;
 	}
 	atomic_inc(&eb->write_locks);
 	atomic_inc(&eb->spinning_writers);
 	eb->lock_owner = current->pid;
 	return 1;
 }

 /*
  * drop a spinning read lock
  */
 void btrfs_tree_read_unlock(struct extent_buffer *eb)
 {
 	/*
 	 * if we're nested, we have the write lock.  No new locking
 	 * is needed as long as we are the lock owner.
 	 * The write unlock will do a barrier for us, and the lock_nested
 	 * field only matters to the lock owner.
 	 */
 	if (eb->lock_nested && current->pid == eb->lock_owner) {
 		eb->lock_nested = 0;
 		return;
 	}
 	btrfs_assert_tree_read_locked(eb);
 	WARN_ON(atomic_read(&eb->spinning_readers) == 0);
 	atomic_dec(&eb->spinning_readers);
 	atomic_dec(&eb->read_locks);
 	read_unlock(&eb->lock);
 }

 /*
  * drop a blocking read lock
  */
 void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
 {
 	/*
 	 * if we're nested, we have the write lock.  No new locking
 	 * is needed as long as we are the lock owner.
 	 * The write unlock will do a barrier for us, and the lock_nested
 	 * field only matters to the lock owner.
 	 */
 	if (eb->lock_nested && current->pid == eb->lock_owner) {
 		eb->lock_nested = 0;
 		return;
 	}
 	btrfs_assert_tree_read_locked(eb);
 	WARN_ON(atomic_read(&eb->blocking_readers) == 0);
 	/*
 	 * atomic_dec_and_test implies a barrier for waitqueue_active
 	 */
 	if (atomic_dec_and_test(&eb->blocking_readers) &&
 	    waitqueue_active(&eb->read_lock_wq))
 		wake_up(&eb->read_lock_wq);
 	atomic_dec(&eb->read_locks);
 }

 /*
  * take a spinning write lock.  This will wait for both
  * blocking readers or writers
  */
 void btrfs_tree_lock(struct extent_buffer *eb)
 {
 	WARN_ON(eb->lock_owner == current->pid);
 again:
 	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
 	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
 	write_lock(&eb->lock);
 	if (atomic_read(&eb->blocking_readers)) {
 		write_unlock(&eb->lock);
 		wait_event(eb->read_lock_wq,
 			   atomic_read(&eb->blocking_readers) == 0);
 		goto again;
 	}
 	if (atomic_read(&eb->blocking_writers)) {
 		write_unlock(&eb->lock);
 		wait_event(eb->write_lock_wq,
 			   atomic_read(&eb->blocking_writers) == 0);
 		goto again;
 	}
 	WARN_ON(atomic_read(&eb->spinning_writers));
 	atomic_inc(&eb->spinning_writers);
 	atomic_inc(&eb->write_locks);
 	eb->lock_owner = current->pid;
 }

 /*
  * drop a spinning or a blocking write lock.
  */
 void btrfs_tree_unlock(struct extent_buffer *eb)
 {
 	int blockers = atomic_read(&eb->blocking_writers);

 	BUG_ON(blockers > 1);

 	btrfs_assert_tree_locked(eb);
 	eb->lock_owner = 0;
 	atomic_dec(&eb->write_locks);

 	if (blockers) {
 		WARN_ON(atomic_read(&eb->spinning_writers));
 		atomic_dec(&eb->blocking_writers);
 		/*
 		 * Make sure counter is updated before we wake up waiters.
 		 */
 		smp_mb();
 		if (waitqueue_active(&eb->write_lock_wq))
 			wake_up(&eb->write_lock_wq);
 	} else {
 		WARN_ON(atomic_read(&eb->spinning_writers) != 1);
 		atomic_dec(&eb->spinning_writers);
 		write_unlock(&eb->lock);
 	}
 }

 void btrfs_assert_tree_locked(struct extent_buffer *eb)
 {
 	BUG_ON(!atomic_read(&eb->write_locks));
 }

 static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
 {
 	BUG_ON(!atomic_read(&eb->read_locks));
 }
	/*
	* Copyright (C) 2008 Oracle. All rights reserved.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public
	* License v2 as published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*
	* You should have received a copy of the GNU General Public
	* License along with this program; if not, write to the
	* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	* Boston, MA 021110-1307, USA.
	*/
	#include <linux/sched.h>
	#include <linux/pagemap.h>
	#include <linux/spinlock.h>
	#include <linux/page-flags.h>
	#include <asm/bug.h>
	#include "ctree.h"
	#include "extent_io.h"
	#include "locking.h"

	static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);

	/*
	* if we currently have a spinning reader or writer lock
	* (indicated by the rw flag) this will bump the count
	* of blocking holders and drop the spinlock.
	*/
	void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
	{
	/*
	* no lock is required. The lock owner may change if
	* we have a read lock, but it won't change to or away
	* from us. If we have the write lock, we are the owner
	* and it'll never change.
	*/
	if (eb->lock_nested && current->pid == eb->lock_owner)
	return;
	if (rw == BTRFS_WRITE_LOCK) {
	if (atomic_read(&eb->blocking_writers) == 0) {
	WARN_ON(atomic_read(&eb->spinning_writers) != 1);
	atomic_dec(&eb->spinning_writers);
	btrfs_assert_tree_locked(eb);
	atomic_inc(&eb->blocking_writers);
	write_unlock(&eb->lock);
	}
	} else if (rw == BTRFS_READ_LOCK) {
	btrfs_assert_tree_read_locked(eb);
	atomic_inc(&eb->blocking_readers);
	WARN_ON(atomic_read(&eb->spinning_readers) == 0);
	atomic_dec(&eb->spinning_readers);
	read_unlock(&eb->lock);
	}
	}

	/*
	* if we currently have a blocking lock, take the spinlock
	* and drop our blocking count
	*/
	void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
	{
	/*
	* no lock is required. The lock owner may change if
	* we have a read lock, but it won't change to or away
	* from us. If we have the write lock, we are the owner
	* and it'll never change.
	*/
	if (eb->lock_nested && current->pid == eb->lock_owner)
	return;

	if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
	BUG_ON(atomic_read(&eb->blocking_writers) != 1);
	write_lock(&eb->lock);
	WARN_ON(atomic_read(&eb->spinning_writers));
	atomic_inc(&eb->spinning_writers);
	/*
	* atomic_dec_and_test implies a barrier for waitqueue_active
	*/
	if (atomic_dec_and_test(&eb->blocking_writers) &&
	waitqueue_active(&eb->write_lock_wq))
	wake_up(&eb->write_lock_wq);
	} else if (rw == BTRFS_READ_LOCK_BLOCKING) {
	BUG_ON(atomic_read(&eb->blocking_readers) == 0);
	read_lock(&eb->lock);
	atomic_inc(&eb->spinning_readers);
	/*
	* atomic_dec_and_test implies a barrier for waitqueue_active
	*/
	if (atomic_dec_and_test(&eb->blocking_readers) &&
	waitqueue_active(&eb->read_lock_wq))
	wake_up(&eb->read_lock_wq);
	}
	}

	/*
	* take a spinning read lock. This will wait for any blocking
	* writers
	*/
	void btrfs_tree_read_lock(struct extent_buffer *eb)
	{
	again:
	BUG_ON(!atomic_read(&eb->blocking_writers) &&
	current->pid == eb->lock_owner);

	read_lock(&eb->lock);
	if (atomic_read(&eb->blocking_writers) &&
	current->pid == eb->lock_owner) {
	/*
	* This extent is already write-locked by our thread. We allow
	* an additional read lock to be added because it's for the same
	* thread. btrfs_find_all_roots() depends on this as it may be
	* called on a partly (write-)locked tree.
	*/
	BUG_ON(eb->lock_nested);
	eb->lock_nested = 1;
	read_unlock(&eb->lock);
	return;
	}
	if (atomic_read(&eb->blocking_writers)) {
	read_unlock(&eb->lock);
	wait_event(eb->write_lock_wq,
	atomic_read(&eb->blocking_writers) == 0);
	goto again;
	}
	atomic_inc(&eb->read_locks);
	atomic_inc(&eb->spinning_readers);
	}

	/*
	* take a spinning read lock.
	* returns 1 if we get the read lock and 0 if we don't
	* this won't wait for blocking writers
	*/
	int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
	{
	if (atomic_read(&eb->blocking_writers))
	return 0;

	read_lock(&eb->lock);
	if (atomic_read(&eb->blocking_writers)) {
	read_unlock(&eb->lock);
	return 0;
	}
	atomic_inc(&eb->read_locks);
	atomic_inc(&eb->spinning_readers);
	return 1;
	}

	/*
	* returns 1 if we get the read lock and 0 if we don't
	* this won't wait for blocking writers
	*/
	int btrfs_try_tree_read_lock(struct extent_buffer *eb)
	{
	if (atomic_read(&eb->blocking_writers))
	return 0;

	if (!read_trylock(&eb->lock))
	return 0;

	if (atomic_read(&eb->blocking_writers)) {
	read_unlock(&eb->lock);
	return 0;
	}
	atomic_inc(&eb->read_locks);
	atomic_inc(&eb->spinning_readers);
	return 1;
	}

	/*
	* returns 1 if we get the read lock and 0 if we don't
	* this won't wait for blocking writers or readers
	*/
	int btrfs_try_tree_write_lock(struct extent_buffer *eb)
	{
	if (atomic_read(&eb->blocking_writers) \|\|
	atomic_read(&eb->blocking_readers))
	return 0;

	write_lock(&eb->lock);
	if (atomic_read(&eb->blocking_writers) \|\|
	atomic_read(&eb->blocking_readers)) {
	write_unlock(&eb->lock);
	return 0;
	}
	atomic_inc(&eb->write_locks);
	atomic_inc(&eb->spinning_writers);
	eb->lock_owner = current->pid;
	return 1;
	}

	/*
	* drop a spinning read lock
	*/
	void btrfs_tree_read_unlock(struct extent_buffer *eb)
	{
	/*
	* if we're nested, we have the write lock. No new locking
	* is needed as long as we are the lock owner.
	* The write unlock will do a barrier for us, and the lock_nested
	* field only matters to the lock owner.
	*/
	if (eb->lock_nested && current->pid == eb->lock_owner) {
	eb->lock_nested = 0;
	return;
	}
	btrfs_assert_tree_read_locked(eb);
	WARN_ON(atomic_read(&eb->spinning_readers) == 0);
	atomic_dec(&eb->spinning_readers);
	atomic_dec(&eb->read_locks);
	read_unlock(&eb->lock);
	}

	/*
	* drop a blocking read lock
	*/
	void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
	{
	/*
	* if we're nested, we have the write lock. No new locking
	* is needed as long as we are the lock owner.
	* The write unlock will do a barrier for us, and the lock_nested
	* field only matters to the lock owner.
	*/
	if (eb->lock_nested && current->pid == eb->lock_owner) {
	eb->lock_nested = 0;
	return;
	}
	btrfs_assert_tree_read_locked(eb);
	WARN_ON(atomic_read(&eb->blocking_readers) == 0);
	/*
	* atomic_dec_and_test implies a barrier for waitqueue_active
	*/
	if (atomic_dec_and_test(&eb->blocking_readers) &&
	waitqueue_active(&eb->read_lock_wq))
	wake_up(&eb->read_lock_wq);
	atomic_dec(&eb->read_locks);
	}

	/*
	* take a spinning write lock. This will wait for both
	* blocking readers or writers
	*/
	void btrfs_tree_lock(struct extent_buffer *eb)
	{
	WARN_ON(eb->lock_owner == current->pid);
	again:
	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
	write_lock(&eb->lock);
	if (atomic_read(&eb->blocking_readers)) {
	write_unlock(&eb->lock);
	wait_event(eb->read_lock_wq,
	atomic_read(&eb->blocking_readers) == 0);
	goto again;
	}
	if (atomic_read(&eb->blocking_writers)) {
	write_unlock(&eb->lock);
	wait_event(eb->write_lock_wq,
	atomic_read(&eb->blocking_writers) == 0);
	goto again;
	}
	WARN_ON(atomic_read(&eb->spinning_writers));
	atomic_inc(&eb->spinning_writers);
	atomic_inc(&eb->write_locks);
	eb->lock_owner = current->pid;
	}

	/*
	* drop a spinning or a blocking write lock.
	*/
	void btrfs_tree_unlock(struct extent_buffer *eb)
	{
	int blockers = atomic_read(&eb->blocking_writers);

	BUG_ON(blockers > 1);

	btrfs_assert_tree_locked(eb);
	eb->lock_owner = 0;
	atomic_dec(&eb->write_locks);

	if (blockers) {
	WARN_ON(atomic_read(&eb->spinning_writers));
	atomic_dec(&eb->blocking_writers);
	/*
	* Make sure counter is updated before we wake up waiters.
	*/
	smp_mb();
	if (waitqueue_active(&eb->write_lock_wq))
	wake_up(&eb->write_lock_wq);
	} else {
	WARN_ON(atomic_read(&eb->spinning_writers) != 1);
	atomic_dec(&eb->spinning_writers);
	write_unlock(&eb->lock);
	}
	}

	void btrfs_assert_tree_locked(struct extent_buffer *eb)
	{
	BUG_ON(!atomic_read(&eb->write_locks));
	}

	static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
	{
	BUG_ON(!atomic_read(&eb->read_locks));
	}