btrfs: switch extent_buffer blocking_writers from atomic to int

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>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 43761ec..6c49db9 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4857,7 +4857,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
        eb->bflags = 0;
        rwlock_init(&eb->lock);
        atomic_set(&eb->blocking_readers, 0);
-       atomic_set(&eb->blocking_writers, 0);
+       eb->blocking_writers = 0;
        eb->lock_nested = false;
        init_waitqueue_head(&eb->write_lock_wq);
        init_waitqueue_head(&eb->read_lock_wq);

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index aa18a16..201da61 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -167,7 +167,7 @@ struct extent_buffer {
        struct rcu_head rcu_head;
        pid_t lock_owner;
 
-       atomic_t blocking_writers;
+       int blocking_writers;
        atomic_t blocking_readers;
        bool lock_nested;
        /* >= 0 if eb belongs to a log tree, -1 otherwise */

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 2f6c3c7..5feb011 100644 (file)
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -111,10 +111,10 @@ void btrfs_set_lock_blocking_write(struct extent_buffer *eb)
         */
        if (eb->lock_nested && current->pid == eb->lock_owner)
                return;
-       if (atomic_read(&eb->blocking_writers) == 0) {
+       if (eb->blocking_writers == 0) {
                btrfs_assert_spinning_writers_put(eb);
                btrfs_assert_tree_locked(eb);
-               atomic_inc(&eb->blocking_writers);
+               eb->blocking_writers++;
                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)
                return;
-       BUG_ON(atomic_read(&eb->blocking_writers) != 1);
        write_lock(&eb->lock);
+       BUG_ON(eb->blocking_writers != 1);
        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);
+       if (--eb->blocking_writers == 0)
+               cond_wake_up(&eb->write_lock_wq);
 }
 
 /*
@@ -167,12 +166,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb)
        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) {
+       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
@@ -185,10 +182,10 @@ again:
                trace_btrfs_tree_read_lock(eb, start_ns);
                return;
        }
-       if (atomic_read(&eb->blocking_writers)) {
+       if (eb->blocking_writers) {
                read_unlock(&eb->lock);
                wait_event(eb->write_lock_wq,
-                          atomic_read(&eb->blocking_writers) == 0);
+                          eb->blocking_writers == 0);
                goto again;
        }
        btrfs_assert_tree_read_locks_get(eb);
@@ -203,11 +200,11 @@ again:
  */
 int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
 {
-       if (atomic_read(&eb->blocking_writers))
+       if (eb->blocking_writers)
                return 0;
 
        read_lock(&eb->lock);
-       if (atomic_read(&eb->blocking_writers)) {
+       if (eb->blocking_writers) {
                read_unlock(&eb->lock);
                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)
 {
-       if (atomic_read(&eb->blocking_writers))
+       if (eb->blocking_writers)
                return 0;
 
        if (!read_trylock(&eb->lock))
                return 0;
 
-       if (atomic_read(&eb->blocking_writers)) {
+       if (eb->blocking_writers) {
                read_unlock(&eb->lock);
                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)
 {
-       if (atomic_read(&eb->blocking_writers) ||
-           atomic_read(&eb->blocking_readers))
+       if (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)) {
+       if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) {
                write_unlock(&eb->lock);
                return 0;
        }
@@ -322,10 +317,9 @@ 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);
+       wait_event(eb->write_lock_wq, eb->blocking_writers == 0);
        write_lock(&eb->lock);
-       if (atomic_read(&eb->blocking_readers) ||
-           atomic_read(&eb->blocking_writers)) {
+       if (atomic_read(&eb->blocking_readers) || eb->blocking_writers) {
                write_unlock(&eb->lock);
                goto again;
        }
@@ -340,7 +334,7 @@ again:
  */
 void btrfs_tree_unlock(struct extent_buffer *eb)
 {
-       int blockers = atomic_read(&eb->blocking_writers);
+       int blockers = eb->blocking_writers;
 
        BUG_ON(blockers > 1);
 
@@ -351,7 +345,7 @@ void btrfs_tree_unlock(struct extent_buffer *eb)
 
        if (blockers) {
                btrfs_assert_no_spinning_writers(eb);
-               atomic_dec(&eb->blocking_writers);
+               eb->blocking_writers--;
                /* Use the lighter barrier after atomic */
                smp_mb__after_atomic();
                cond_wake_up_nomb(&eb->write_lock_wq);

diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
index 1141ca5..7cb4f1f 100644 (file)
--- a/fs/btrfs/print-tree.c
+++ b/fs/btrfs/print-tree.c
@@ -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",
                   atomic_read(&eb->refs), atomic_read(&eb->write_locks),
                   atomic_read(&eb->read_locks),
-                  atomic_read(&eb->blocking_writers),
+                  eb->blocking_writers,
                   atomic_read(&eb->blocking_readers),
                   atomic_read(&eb->spinning_writers),
                   atomic_read(&eb->spinning_readers),