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btrfs: switch extent_buffer blocking_writers from atomic to int

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The blocking_writers is either 0 or 1 and always updated under the lock,
so we don't need the atomic_t semantics.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2019-05-02 16:47:23 +02:00
parent 38e9372e39
commit 06297d8cef
4 changed files with 23 additions and 29 deletions

2
fs/btrfs/extent_io.c
View File

@ -4857,7 +4857,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
eb->bflags = 0; eb->bflags = 0;
rwlock_init(&eb->lock); rwlock_init(&eb->lock);
atomic_set(&eb->blocking_readers, 0); atomic_set(&eb->blocking_readers, 0);
atomic_set(&eb->blocking_writers, 0); eb->blocking_writers = 0;
eb->lock_nested = false; eb->lock_nested = false;
init_waitqueue_head(&eb->write_lock_wq); init_waitqueue_head(&eb->write_lock_wq);
init_waitqueue_head(&eb->read_lock_wq); init_waitqueue_head(&eb->read_lock_wq);

2
fs/btrfs/extent_io.h
View File

@ -167,7 +167,7 @@ struct extent_buffer {
struct rcu_head rcu_head; struct rcu_head rcu_head;
pid_t lock_owner; pid_t lock_owner;
atomic_t blocking_writers; int blocking_writers;
atomic_t blocking_readers; atomic_t blocking_readers;
bool lock_nested; bool lock_nested;
/* >= 0 if eb belongs to a log tree, -1 otherwise */ /* >= 0 if eb belongs to a log tree, -1 otherwise */

46
fs/btrfs/locking.c
View File

@ -111,10 +111,10 @@ void btrfs_set_lock_blocking_write(struct extent_buffer *eb)
*/ */
if (eb->lock_nested && current->pid == eb->lock_owner) if (eb->lock_nested && current->pid == eb->lock_owner)
return; return;
if (atomic_read(&eb->blocking_writers) == 0) { if (eb->blocking_writers == 0) {
btrfs_assert_spinning_writers_put(eb); btrfs_assert_spinning_writers_put(eb);
btrfs_assert_tree_locked(eb); btrfs_assert_tree_locked(eb);
atomic_inc(&eb->blocking_writers); eb->blocking_writers++;
write_unlock(&eb->lock); write_unlock(&eb->lock);
} }
} }
@ -148,12 +148,11 @@ void btrfs_clear_lock_blocking_write(struct extent_buffer *eb)
*/ */
if (eb->lock_nested && current->pid == eb->lock_owner) if (eb->lock_nested && current->pid == eb->lock_owner)
return; return;
BUG_ON(atomic_read(&eb->blocking_writers) != 1);
write_lock(&eb->lock); write_lock(&eb->lock);
BUG_ON(eb->blocking_writers != 1);
btrfs_assert_spinning_writers_get(eb); btrfs_assert_spinning_writers_get(eb);
/* atomic_dec_and_test implies a barrier */ if (--eb->blocking_writers == 0)
if (atomic_dec_and_test(&eb->blocking_writers)) cond_wake_up(&eb->write_lock_wq);
cond_wake_up_nomb(&eb->write_lock_wq);
} }
/* /*
@ -167,12 +166,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb)
if (trace_btrfs_tree_read_lock_enabled()) if (trace_btrfs_tree_read_lock_enabled())
start_ns = ktime_get_ns(); start_ns = ktime_get_ns();
again: again:
BUG_ON(!atomic_read(&eb->blocking_writers) &&
current->pid == eb->lock_owner);
read_lock(&eb->lock); read_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers) && BUG_ON(eb->blocking_writers == 0 &&
current->pid == eb->lock_owner) { 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 * This extent is already write-locked by our thread. We allow
* an additional read lock to be added because it's for the same * an additional read lock to be added because it's for the same
@ -185,10 +182,10 @@ again:
trace_btrfs_tree_read_lock(eb, start_ns); trace_btrfs_tree_read_lock(eb, start_ns);
return; return;
} }
if (atomic_read(&eb->blocking_writers)) { if (eb->blocking_writers) {
read_unlock(&eb->lock); read_unlock(&eb->lock);
wait_event(eb->write_lock_wq, wait_event(eb->write_lock_wq,
atomic_read(&eb->blocking_writers) == 0); eb->blocking_writers == 0);
goto again; goto again;
} }
btrfs_assert_tree_read_locks_get(eb); btrfs_assert_tree_read_locks_get(eb);
@ -203,11 +200,11 @@ again:
*/ */
int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
{ {
if (atomic_read(&eb->blocking_writers)) if (eb->blocking_writers)
return 0; return 0;
read_lock(&eb->lock); read_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers)) { if (eb->blocking_writers) {
read_unlock(&eb->lock); read_unlock(&eb->lock);
return 0; return 0;
} }
@ -223,13 +220,13 @@ int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
*/ */
int btrfs_try_tree_read_lock(struct extent_buffer *eb) int btrfs_try_tree_read_lock(struct extent_buffer *eb)
{ {
if (atomic_read(&eb->blocking_writers)) if (eb->blocking_writers)
return 0; return 0;
if (!read_trylock(&eb->lock)) if (!read_trylock(&eb->lock))
return 0; return 0;
if (atomic_read(&eb->blocking_writers)) { if (eb->blocking_writers) {
read_unlock(&eb->lock); read_unlock(&eb->lock);
return 0; return 0;
} }
@ -245,13 +242,11 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb)
*/ */
int btrfs_try_tree_write_lock(struct extent_buffer *eb) int btrfs_try_tree_write_lock(struct extent_buffer *eb)
{ {
if (atomic_read(&eb->blocking_writers) || if (eb->blocking_writers || atomic_read(&eb->blocking_readers))
atomic_read(&eb->blocking_readers))
return 0; return 0;
write_lock(&eb->lock); write_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers) || if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) {
atomic_read(&eb->blocking_readers)) {
write_unlock(&eb->lock); write_unlock(&eb->lock);
return 0; return 0;
} }
@ -322,10 +317,9 @@ void btrfs_tree_lock(struct extent_buffer *eb)
WARN_ON(eb->lock_owner == current->pid); WARN_ON(eb->lock_owner == current->pid);
again: again:
wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0); wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); wait_event(eb->write_lock_wq, eb->blocking_writers == 0);
write_lock(&eb->lock); write_lock(&eb->lock);
if (atomic_read(&eb->blocking_readers) || if (atomic_read(&eb->blocking_readers) || eb->blocking_writers) {
atomic_read(&eb->blocking_writers)) {
write_unlock(&eb->lock); write_unlock(&eb->lock);
goto again; goto again;
} }
@ -340,7 +334,7 @@ again:
*/ */
void btrfs_tree_unlock(struct extent_buffer *eb) void btrfs_tree_unlock(struct extent_buffer *eb)
{ {
int blockers = atomic_read(&eb->blocking_writers); int blockers = eb->blocking_writers;
BUG_ON(blockers > 1); BUG_ON(blockers > 1);
@ -351,7 +345,7 @@ void btrfs_tree_unlock(struct extent_buffer *eb)
if (blockers) { if (blockers) {
btrfs_assert_no_spinning_writers(eb); btrfs_assert_no_spinning_writers(eb);
atomic_dec(&eb->blocking_writers); eb->blocking_writers--;
/* Use the lighter barrier after atomic */ /* Use the lighter barrier after atomic */
smp_mb__after_atomic(); smp_mb__after_atomic();
cond_wake_up_nomb(&eb->write_lock_wq); cond_wake_up_nomb(&eb->write_lock_wq);

2
fs/btrfs/print-tree.c
View File

@ -155,7 +155,7 @@ static void print_eb_refs_lock(struct extent_buffer *eb)
"refs %u lock (w:%d r:%d bw:%d br:%d sw:%d sr:%d) lock_owner %u current %u", "refs %u lock (w:%d r:%d bw:%d br:%d sw:%d sr:%d) lock_owner %u current %u",
atomic_read(&eb->refs), atomic_read(&eb->write_locks), atomic_read(&eb->refs), atomic_read(&eb->write_locks),
atomic_read(&eb->read_locks), atomic_read(&eb->read_locks),
atomic_read(&eb->blocking_writers), eb->blocking_writers,
atomic_read(&eb->blocking_readers), atomic_read(&eb->blocking_readers),
atomic_read(&eb->spinning_writers), atomic_read(&eb->spinning_writers),
atomic_read(&eb->spinning_readers), atomic_read(&eb->spinning_readers),