btrfs: add comments to barriers before waitqueue_active

Reduce number of undocumented barriers out there.

Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 57ee8ca..3a9317c 100644 (file)
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -839,6 +839,9 @@ static void free_workspace(int type, struct list_head *workspace)
        btrfs_compress_op[idx]->free_workspace(workspace);
        atomic_dec(alloc_workspace);
 wake:
+       /*
+        * Make sure counter is updated before we wake up waiters.
+        */
        smp_mb();
        if (waitqueue_active(workspace_wait))
                wake_up(workspace_wait);

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 9f96042..59eb92f 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10363,8 +10363,7 @@ void btrfs_end_write_no_snapshoting(struct btrfs_root *root)
 {
        percpu_counter_dec(&root->subv_writers->counter);
        /*
-        * Make sure counter is updated before we wake up
-        * waiters.
+        * Make sure counter is updated before we wake up waiters.
         */
        smp_mb();
        if (waitqueue_active(&root->subv_writers->wait))

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index d7e6baf..03f8630 100644 (file)
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -280,6 +280,9 @@ void btrfs_tree_unlock(struct extent_buffer *eb)
        if (blockers) {
                WARN_ON(atomic_read(&eb->spinning_writers));
                atomic_dec(&eb->blocking_writers);
+               /*
+                * Make sure counter is updated before we wake up waiters.
+                */
                smp_mb();
                if (waitqueue_active(&eb->write_lock_wq))
                        wake_up(&eb->write_lock_wq);

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 52170cf..071005f 100644 (file)
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -345,6 +345,9 @@ int btrfs_dec_test_first_ordered_pending(struct inode *inode,
 
        if (entry->bytes_left == 0) {
                ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
+               /*
+                * Implicit memory barrier after test_and_set_bit
+                */
                if (waitqueue_active(&entry->wait))
                        wake_up(&entry->wait);
        } else {
@@ -409,6 +412,9 @@ have_entry:
 
        if (entry->bytes_left == 0) {
                ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
+               /*
+                * Implicit memory barrier after test_and_set_bit
+                */
                if (waitqueue_active(&entry->wait))
                        wake_up(&entry->wait);
        } else {

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index e8e5b5a..3fd70f7 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -861,6 +861,9 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
        atomic_dec(&cur_trans->num_writers);
        extwriter_counter_dec(cur_trans, trans->type);
 
+       /*
+        * Make sure counter is updated before we wake up waiters.
+        */
        smp_mb();
        if (waitqueue_active(&cur_trans->writer_wait))
                wake_up(&cur_trans->writer_wait);