btrfs: add comments to barriers before waitqueue_active
Reduce number of undocumented barriers out there.
Signed-off-by: David Sterba <[email protected]>
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 57ee8ca..3a9317c 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -839,6 +839,9 @@
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
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10363,8 +10363,7 @@
{
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..03f8630d 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -280,6 +280,9 @@
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
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -345,6 +345,9 @@
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 @@
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
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -861,6 +861,9 @@
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);
