linux/fs/btrfs/locking.c
David Sterba 602cbe91fb btrfs: move cond_wake_up functions out of ctree
The file ctree.h serves as a header for everything and has become quite
bloated. Split some helpers that are generic and create a new file that
should be the catch-all for code that's not btrfs-specific.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: David Sterba <dsterba@suse.com>
2019-09-09 14:59:15 +02:00

325 lines
8.5 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2008 Oracle. All rights reserved.
*/
#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/spinlock.h>
#include <linux/page-flags.h>
#include <asm/bug.h>
#include "misc.h"
#include "ctree.h"
#include "extent_io.h"
#include "locking.h"
#ifdef CONFIG_BTRFS_DEBUG
static void btrfs_assert_spinning_writers_get(struct extent_buffer *eb)
{
WARN_ON(eb->spinning_writers);
eb->spinning_writers++;
}
static void btrfs_assert_spinning_writers_put(struct extent_buffer *eb)
{
WARN_ON(eb->spinning_writers != 1);
eb->spinning_writers--;
}
static void btrfs_assert_no_spinning_writers(struct extent_buffer *eb)
{
WARN_ON(eb->spinning_writers);
}
static void btrfs_assert_spinning_readers_get(struct extent_buffer *eb)
{
atomic_inc(&eb->spinning_readers);
}
static void btrfs_assert_spinning_readers_put(struct extent_buffer *eb)
{
WARN_ON(atomic_read(&eb->spinning_readers) == 0);
atomic_dec(&eb->spinning_readers);
}
static void btrfs_assert_tree_read_locks_get(struct extent_buffer *eb)
{
atomic_inc(&eb->read_locks);
}
static void btrfs_assert_tree_read_locks_put(struct extent_buffer *eb)
{
atomic_dec(&eb->read_locks);
}
static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
{
BUG_ON(!atomic_read(&eb->read_locks));
}
static void btrfs_assert_tree_write_locks_get(struct extent_buffer *eb)
{
eb->write_locks++;
}
static void btrfs_assert_tree_write_locks_put(struct extent_buffer *eb)
{
eb->write_locks--;
}
void btrfs_assert_tree_locked(struct extent_buffer *eb)
{
BUG_ON(!eb->write_locks);
}
#else
static void btrfs_assert_spinning_writers_get(struct extent_buffer *eb) { }
static void btrfs_assert_spinning_writers_put(struct extent_buffer *eb) { }
static void btrfs_assert_no_spinning_writers(struct extent_buffer *eb) { }
static void btrfs_assert_spinning_readers_put(struct extent_buffer *eb) { }
static void btrfs_assert_spinning_readers_get(struct extent_buffer *eb) { }
static void btrfs_assert_tree_read_locked(struct extent_buffer *eb) { }
static void btrfs_assert_tree_read_locks_get(struct extent_buffer *eb) { }
static void btrfs_assert_tree_read_locks_put(struct extent_buffer *eb) { }
void btrfs_assert_tree_locked(struct extent_buffer *eb) { }
static void btrfs_assert_tree_write_locks_get(struct extent_buffer *eb) { }
static void btrfs_assert_tree_write_locks_put(struct extent_buffer *eb) { }
#endif
void btrfs_set_lock_blocking_read(struct extent_buffer *eb)
{
trace_btrfs_set_lock_blocking_read(eb);
/*
* 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;
btrfs_assert_tree_read_locked(eb);
atomic_inc(&eb->blocking_readers);
btrfs_assert_spinning_readers_put(eb);
read_unlock(&eb->lock);
}
void btrfs_set_lock_blocking_write(struct extent_buffer *eb)
{
trace_btrfs_set_lock_blocking_write(eb);
/*
* 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 (eb->blocking_writers == 0) {
btrfs_assert_spinning_writers_put(eb);
btrfs_assert_tree_locked(eb);
eb->blocking_writers++;
write_unlock(&eb->lock);
}
}
/*
* take a spinning read lock. This will wait for any blocking
* writers
*/
void btrfs_tree_read_lock(struct extent_buffer *eb)
{
u64 start_ns = 0;
if (trace_btrfs_tree_read_lock_enabled())
start_ns = ktime_get_ns();
again:
read_lock(&eb->lock);
BUG_ON(eb->blocking_writers == 0 &&
current->pid == eb->lock_owner);
if (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 = true;
read_unlock(&eb->lock);
trace_btrfs_tree_read_lock(eb, start_ns);
return;
}
if (eb->blocking_writers) {
read_unlock(&eb->lock);
wait_event(eb->write_lock_wq,
eb->blocking_writers == 0);
goto again;
}
btrfs_assert_tree_read_locks_get(eb);
btrfs_assert_spinning_readers_get(eb);
trace_btrfs_tree_read_lock(eb, start_ns);
}
/*
* 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 (eb->blocking_writers)
return 0;
read_lock(&eb->lock);
if (eb->blocking_writers) {
read_unlock(&eb->lock);
return 0;
}
btrfs_assert_tree_read_locks_get(eb);
btrfs_assert_spinning_readers_get(eb);
trace_btrfs_tree_read_lock_atomic(eb);
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 (eb->blocking_writers)
return 0;
if (!read_trylock(&eb->lock))
return 0;
if (eb->blocking_writers) {
read_unlock(&eb->lock);
return 0;
}
btrfs_assert_tree_read_locks_get(eb);
btrfs_assert_spinning_readers_get(eb);
trace_btrfs_try_tree_read_lock(eb);
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 (eb->blocking_writers || atomic_read(&eb->blocking_readers))
return 0;
write_lock(&eb->lock);
if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) {
write_unlock(&eb->lock);
return 0;
}
btrfs_assert_tree_write_locks_get(eb);
btrfs_assert_spinning_writers_get(eb);
eb->lock_owner = current->pid;
trace_btrfs_try_tree_write_lock(eb);
return 1;
}
/*
* drop a spinning read lock
*/
void btrfs_tree_read_unlock(struct extent_buffer *eb)
{
trace_btrfs_tree_read_unlock(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 = false;
return;
}
btrfs_assert_tree_read_locked(eb);
btrfs_assert_spinning_readers_put(eb);
btrfs_assert_tree_read_locks_put(eb);
read_unlock(&eb->lock);
}
/*
* drop a blocking read lock
*/
void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
{
trace_btrfs_tree_read_unlock_blocking(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 = false;
return;
}
btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->blocking_readers) == 0);
/* atomic_dec_and_test implies a barrier */
if (atomic_dec_and_test(&eb->blocking_readers))
cond_wake_up_nomb(&eb->read_lock_wq);
btrfs_assert_tree_read_locks_put(eb);
}
/*
* take a spinning write lock. This will wait for both
* blocking readers or writers
*/
void btrfs_tree_lock(struct extent_buffer *eb)
{
u64 start_ns = 0;
if (trace_btrfs_tree_lock_enabled())
start_ns = ktime_get_ns();
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, eb->blocking_writers == 0);
write_lock(&eb->lock);
if (atomic_read(&eb->blocking_readers) || eb->blocking_writers) {
write_unlock(&eb->lock);
goto again;
}
btrfs_assert_spinning_writers_get(eb);
btrfs_assert_tree_write_locks_get(eb);
eb->lock_owner = current->pid;
trace_btrfs_tree_lock(eb, start_ns);
}
/*
* drop a spinning or a blocking write lock.
*/
void btrfs_tree_unlock(struct extent_buffer *eb)
{
int blockers = eb->blocking_writers;
BUG_ON(blockers > 1);
btrfs_assert_tree_locked(eb);
trace_btrfs_tree_unlock(eb);
eb->lock_owner = 0;
btrfs_assert_tree_write_locks_put(eb);
if (blockers) {
btrfs_assert_no_spinning_writers(eb);
eb->blocking_writers--;
/*
* We need to order modifying blocking_writers above with
* actually waking up the sleepers to ensure they see the
* updated value of blocking_writers
*/
cond_wake_up(&eb->write_lock_wq);
} else {
btrfs_assert_spinning_writers_put(eb);
write_unlock(&eb->lock);
}
}