[mirror_ubuntu-bionic-kernel.git] / fs / btrfs / locking.c

/*
 * 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)
{
	if (eb->lock_nested) {
		read_lock(&eb->lock);
		if (eb->lock_nested && current->pid == eb->lock_owner) {
			read_unlock(&eb->lock);
			return;
		}
		read_unlock(&eb->lock);
	}
	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);
	}
	return;
}

/*
 * 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)
{
	if (eb->lock_nested) {
		read_lock(&eb->lock);
		if (eb->lock_nested && current->pid == eb->lock_owner) {
			read_unlock(&eb->lock);
			return;
		}
		read_unlock(&eb->lock);
	}
	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);
		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);
		if (atomic_dec_and_test(&eb->blocking_readers) &&
		    waitqueue_active(&eb->read_lock_wq))
			wake_up(&eb->read_lock_wq);
	}
	return;
}

/*
 * take a spinning read lock.  This will wait for any blocking
 * writers
 */
void btrfs_tree_read_lock(struct extent_buffer *eb)
{
again:
	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);
}

/*
 * 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;

	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 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 (eb->lock_nested) {
		read_lock(&eb->lock);
		if (eb->lock_nested && current->pid == eb->lock_owner) {
			eb->lock_nested = 0;
			read_unlock(&eb->lock);
			return;
		}
		read_unlock(&eb->lock);
	}
	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 (eb->lock_nested) {
		read_lock(&eb->lock);
		if (eb->lock_nested && current->pid == eb->lock_owner) {
			eb->lock_nested = 0;
			read_unlock(&eb->lock);
			return;
		}
		read_unlock(&eb->lock);
	}
	btrfs_assert_tree_read_locked(eb);
	WARN_ON(atomic_read(&eb->blocking_readers) == 0);
	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)
{
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);
	atomic_dec(&eb->write_locks);

	if (blockers) {
		WARN_ON(atomic_read(&eb->spinning_writers));
		atomic_dec(&eb->blocking_writers);
		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));
}
Commit	Line	Data
	1	/*
	2	* Copyright (C) 2008 Oracle. All rights reserved.
	3	*
	4	* This program is free software; you can redistribute it and/or
	5	* modify it under the terms of the GNU General Public
	6	* License v2 as published by the Free Software Foundation.
	7	*
	8	* This program is distributed in the hope that it will be useful,
	9	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	10	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	11	* General Public License for more details.
	12	*
	13	* You should have received a copy of the GNU General Public
	14	* License along with this program; if not, write to the
	15	* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	16	* Boston, MA 021110-1307, USA.
	17	*/
	18	#include <linux/sched.h>
	19	#include <linux/pagemap.h>
	20	#include <linux/spinlock.h>
	21	#include <linux/page-flags.h>
	22	#include <asm/bug.h>
	23	#include "ctree.h"
	24	#include "extent_io.h"
	25	#include "locking.h"
	26
	27	static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
	28
	29	/*
	30	* if we currently have a spinning reader or writer lock
	31	* (indicated by the rw flag) this will bump the count
	32	* of blocking holders and drop the spinlock.
	33	*/
	34	void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
	35	{
	36	if (eb->lock_nested) {
	37	read_lock(&eb->lock);
	38	if (eb->lock_nested && current->pid == eb->lock_owner) {
	39	read_unlock(&eb->lock);
	40	return;
	41	}
	42	read_unlock(&eb->lock);
	43	}
	44	if (rw == BTRFS_WRITE_LOCK) {
	45	if (atomic_read(&eb->blocking_writers) == 0) {
	46	WARN_ON(atomic_read(&eb->spinning_writers) != 1);
	47	atomic_dec(&eb->spinning_writers);
	48	btrfs_assert_tree_locked(eb);
	49	atomic_inc(&eb->blocking_writers);
	50	write_unlock(&eb->lock);
	51	}
	52	} else if (rw == BTRFS_READ_LOCK) {
	53	btrfs_assert_tree_read_locked(eb);
	54	atomic_inc(&eb->blocking_readers);
	55	WARN_ON(atomic_read(&eb->spinning_readers) == 0);
	56	atomic_dec(&eb->spinning_readers);
	57	read_unlock(&eb->lock);
	58	}
	59	return;
	60	}
	61
	62	/*
	63	* if we currently have a blocking lock, take the spinlock
	64	* and drop our blocking count
	65	*/
	66	void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
	67	{
	68	if (eb->lock_nested) {
	69	read_lock(&eb->lock);
	70	if (eb->lock_nested && current->pid == eb->lock_owner) {
	71	read_unlock(&eb->lock);
	72	return;
	73	}
	74	read_unlock(&eb->lock);
	75	}
	76	if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
	77	BUG_ON(atomic_read(&eb->blocking_writers) != 1);
	78	write_lock(&eb->lock);
	79	WARN_ON(atomic_read(&eb->spinning_writers));
	80	atomic_inc(&eb->spinning_writers);
	81	if (atomic_dec_and_test(&eb->blocking_writers) &&
	82	waitqueue_active(&eb->write_lock_wq))
	83	wake_up(&eb->write_lock_wq);
	84	} else if (rw == BTRFS_READ_LOCK_BLOCKING) {
	85	BUG_ON(atomic_read(&eb->blocking_readers) == 0);
	86	read_lock(&eb->lock);
	87	atomic_inc(&eb->spinning_readers);
	88	if (atomic_dec_and_test(&eb->blocking_readers) &&
	89	waitqueue_active(&eb->read_lock_wq))
	90	wake_up(&eb->read_lock_wq);
	91	}
	92	return;
	93	}
	94
	95	/*
	96	* take a spinning read lock. This will wait for any blocking
	97	* writers
	98	*/
	99	void btrfs_tree_read_lock(struct extent_buffer *eb)
	100	{
	101	again:
	102	read_lock(&eb->lock);
	103	if (atomic_read(&eb->blocking_writers) &&
	104	current->pid == eb->lock_owner) {
	105	/*
	106	* This extent is already write-locked by our thread. We allow
	107	* an additional read lock to be added because it's for the same
	108	* thread. btrfs_find_all_roots() depends on this as it may be
	109	* called on a partly (write-)locked tree.
	110	*/
	111	BUG_ON(eb->lock_nested);
	112	eb->lock_nested = 1;
	113	read_unlock(&eb->lock);
	114	return;
	115	}
	116	if (atomic_read(&eb->blocking_writers)) {
	117	read_unlock(&eb->lock);
	118	wait_event(eb->write_lock_wq,
	119	atomic_read(&eb->blocking_writers) == 0);
	120	goto again;
	121	}
	122	atomic_inc(&eb->read_locks);
	123	atomic_inc(&eb->spinning_readers);
	124	}
	125
	126	/*
	127	* returns 1 if we get the read lock and 0 if we don't
	128	* this won't wait for blocking writers
	129	*/
	130	int btrfs_try_tree_read_lock(struct extent_buffer *eb)
	131	{
	132	if (atomic_read(&eb->blocking_writers))
	133	return 0;
	134
	135	read_lock(&eb->lock);
	136	if (atomic_read(&eb->blocking_writers)) {
	137	read_unlock(&eb->lock);
	138	return 0;
	139	}
	140	atomic_inc(&eb->read_locks);
	141	atomic_inc(&eb->spinning_readers);
	142	return 1;
	143	}
	144
	145	/*
	146	* returns 1 if we get the read lock and 0 if we don't
	147	* this won't wait for blocking writers or readers
	148	*/
	149	int btrfs_try_tree_write_lock(struct extent_buffer *eb)
	150	{
	151	if (atomic_read(&eb->blocking_writers) \|\|
	152	atomic_read(&eb->blocking_readers))
	153	return 0;
	154	write_lock(&eb->lock);
	155	if (atomic_read(&eb->blocking_writers) \|\|
	156	atomic_read(&eb->blocking_readers)) {
	157	write_unlock(&eb->lock);
	158	return 0;
	159	}
	160	atomic_inc(&eb->write_locks);
	161	atomic_inc(&eb->spinning_writers);
	162	eb->lock_owner = current->pid;
	163	return 1;
	164	}
	165
	166	/*
	167	* drop a spinning read lock
	168	*/
	169	void btrfs_tree_read_unlock(struct extent_buffer *eb)
	170	{
	171	if (eb->lock_nested) {
	172	read_lock(&eb->lock);
	173	if (eb->lock_nested && current->pid == eb->lock_owner) {
	174	eb->lock_nested = 0;
	175	read_unlock(&eb->lock);
	176	return;
	177	}
	178	read_unlock(&eb->lock);
	179	}
	180	btrfs_assert_tree_read_locked(eb);
	181	WARN_ON(atomic_read(&eb->spinning_readers) == 0);
	182	atomic_dec(&eb->spinning_readers);
	183	atomic_dec(&eb->read_locks);
	184	read_unlock(&eb->lock);
	185	}
	186
	187	/*
	188	* drop a blocking read lock
	189	*/
	190	void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
	191	{
	192	if (eb->lock_nested) {
	193	read_lock(&eb->lock);
	194	if (eb->lock_nested && current->pid == eb->lock_owner) {
	195	eb->lock_nested = 0;
	196	read_unlock(&eb->lock);
	197	return;
	198	}
	199	read_unlock(&eb->lock);
	200	}
	201	btrfs_assert_tree_read_locked(eb);
	202	WARN_ON(atomic_read(&eb->blocking_readers) == 0);
	203	if (atomic_dec_and_test(&eb->blocking_readers) &&
	204	waitqueue_active(&eb->read_lock_wq))
	205	wake_up(&eb->read_lock_wq);
	206	atomic_dec(&eb->read_locks);
	207	}
	208
	209	/*
	210	* take a spinning write lock. This will wait for both
	211	* blocking readers or writers
	212	*/
	213	void btrfs_tree_lock(struct extent_buffer *eb)
	214	{
	215	again:
	216	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
	217	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
	218	write_lock(&eb->lock);
	219	if (atomic_read(&eb->blocking_readers)) {
	220	write_unlock(&eb->lock);
	221	wait_event(eb->read_lock_wq,
	222	atomic_read(&eb->blocking_readers) == 0);
	223	goto again;
	224	}
	225	if (atomic_read(&eb->blocking_writers)) {
	226	write_unlock(&eb->lock);
	227	wait_event(eb->write_lock_wq,
	228	atomic_read(&eb->blocking_writers) == 0);
	229	goto again;
	230	}
	231	WARN_ON(atomic_read(&eb->spinning_writers));
	232	atomic_inc(&eb->spinning_writers);
	233	atomic_inc(&eb->write_locks);
	234	eb->lock_owner = current->pid;
	235	}
	236
	237	/*
	238	* drop a spinning or a blocking write lock.
	239	*/
	240	void btrfs_tree_unlock(struct extent_buffer *eb)
	241	{
	242	int blockers = atomic_read(&eb->blocking_writers);
	243
	244	BUG_ON(blockers > 1);
	245
	246	btrfs_assert_tree_locked(eb);
	247	atomic_dec(&eb->write_locks);
	248
	249	if (blockers) {
	250	WARN_ON(atomic_read(&eb->spinning_writers));
	251	atomic_dec(&eb->blocking_writers);
	252	smp_mb();
	253	if (waitqueue_active(&eb->write_lock_wq))
	254	wake_up(&eb->write_lock_wq);
	255	} else {
	256	WARN_ON(atomic_read(&eb->spinning_writers) != 1);
	257	atomic_dec(&eb->spinning_writers);
	258	write_unlock(&eb->lock);
	259	}
	260	}
	261
	262	void btrfs_assert_tree_locked(struct extent_buffer *eb)
	263	{
	264	BUG_ON(!atomic_read(&eb->write_locks));
	265	}
	266
	267	static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
	268	{
	269	BUG_ON(!atomic_read(&eb->read_locks));
	270	}