swh:1:snp:173f8deb0c56c557784b4fd217e7608ac6197844
Tip revision: 9e0babf2c06c73cda2c0cd37a1653d823adb40ec authored by Linus Torvalds on 16 June 2019, 18:49:45 UTC
Linux 5.2-rc5
Linux 5.2-rc5
Tip revision: 9e0babf
locking.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 "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(atomic_read(&eb->spinning_writers));
atomic_inc(&eb->spinning_writers);
}
static void btrfs_assert_spinning_writers_put(struct extent_buffer *eb)
{
WARN_ON(atomic_read(&eb->spinning_writers) != 1);
atomic_dec(&eb->spinning_writers);
}
static void btrfs_assert_no_spinning_writers(struct extent_buffer *eb)
{
WARN_ON(atomic_read(&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)
{
atomic_inc(&eb->write_locks);
}
static void btrfs_assert_tree_write_locks_put(struct extent_buffer *eb)
{
atomic_dec(&eb->write_locks);
}
void btrfs_assert_tree_locked(struct extent_buffer *eb)
{
BUG_ON(!atomic_read(&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 (atomic_read(&eb->blocking_writers) == 0) {
btrfs_assert_spinning_writers_put(eb);
btrfs_assert_tree_locked(eb);
atomic_inc(&eb->blocking_writers);
write_unlock(&eb->lock);
}
}
void btrfs_clear_lock_blocking_read(struct extent_buffer *eb)
{
trace_btrfs_clear_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;
BUG_ON(atomic_read(&eb->blocking_readers) == 0);
read_lock(&eb->lock);
btrfs_assert_spinning_readers_get(eb);
/* atomic_dec_and_test implies a barrier */
if (atomic_dec_and_test(&eb->blocking_readers))
cond_wake_up_nomb(&eb->read_lock_wq);
}
void btrfs_clear_lock_blocking_write(struct extent_buffer *eb)
{
trace_btrfs_clear_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;
BUG_ON(atomic_read(&eb->blocking_writers) != 1);
write_lock(&eb->lock);
btrfs_assert_spinning_writers_get(eb);
/* atomic_dec_and_test implies a barrier */
if (atomic_dec_and_test(&eb->blocking_writers))
cond_wake_up_nomb(&eb->write_lock_wq);
}
/*
* 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:
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 = true;
read_unlock(&eb->lock);
trace_btrfs_tree_read_lock(eb, start_ns);
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;
}
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 (atomic_read(&eb->blocking_writers))
return 0;
read_lock(&eb->lock);
if (atomic_read(&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 (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;
}
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 (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;
}
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, atomic_read(&eb->blocking_writers) == 0);
write_lock(&eb->lock);
if (atomic_read(&eb->blocking_readers) ||
atomic_read(&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 = atomic_read(&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);
atomic_dec(&eb->blocking_writers);
/* Use the lighter barrier after atomic */
smp_mb__after_atomic();
cond_wake_up_nomb(&eb->write_lock_wq);
} else {
btrfs_assert_spinning_writers_put(eb);
write_unlock(&eb->lock);
}
}