Btrfs: barrier before waitqueue_active

We need a barrir before calling waitqueue_active otherwise we will miss
wakeups.  So in places that do atomic_dec(); then atomic_read() use
atomic_dec_return() which imply a memory barrier (see memory-barriers.txt)
and then add an explicit memory barrier everywhere else that need them.
Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

5 files changed, 10 insertions, 12 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 86eff48dab78..43d1c5a3a030 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -818,6 +818,7 @@ static void free_workspace(int type, struct list_head *workspace)
         btrfs_compress_op[idx]->free_workspace(workspace);
         atomic_dec(alloc_workspace);
 wake:
+        smp_mb();
         if (waitqueue_active(workspace_wait))
                 wake_up(workspace_wait);
 }
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 00deed4ef3ed..07d5eeb1e6f1 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -512,8 +512,8 @@ static void __btrfs_remove_delayed_item(struct btrfs_delayed_item *delayed_item)
 
         rb_erase(&delayed_item->rb_node, root);
         delayed_item->delayed_node->count--;
-        atomic_dec(&delayed_root->items);
-        if (atomic_read(&delayed_root->items) < BTRFS_DELAYED_BACKGROUND &&
+        if (atomic_dec_return(&delayed_root->items) <
+            BTRFS_DELAYED_BACKGROUND &&
             waitqueue_active(&delayed_root->wait))
                 wake_up(&delayed_root->wait);
 }
@@ -1056,8 +1056,7 @@ static void btrfs_release_delayed_inode(struct btrfs_delayed_node *delayed_node)
                 delayed_node->count--;
 
                 delayed_root = delayed_node->root->fs_info->delayed_root;
-                atomic_dec(&delayed_root->items);
-                if (atomic_read(&delayed_root->items) <
+                if (atomic_dec_return(&delayed_root->items) <
                     BTRFS_DELAYED_BACKGROUND &&
                     waitqueue_active(&delayed_root->wait))
                         wake_up(&delayed_root->wait);
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a7ad8fc8dc53..dd86a5d88428 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -754,9 +754,7 @@ static void run_one_async_done(struct btrfs_work *work)
         limit = btrfs_async_submit_limit(fs_info);
         limit = limit * 2 / 3;
 
-        atomic_dec(&fs_info->nr_async_submits);
-
-        if (atomic_read(&fs_info->nr_async_submits) < limit &&
+        if (atomic_dec_return(&fs_info->nr_async_submits) < limit &&
             waitqueue_active(&fs_info->async_submit_wait))
                 wake_up(&fs_info->async_submit_wait);
 
@@ -3783,14 +3781,17 @@ int btrfs_cleanup_transaction(struct btrfs_root *root)
                 /* FIXME: cleanup wait for commit */
                 t->in_commit = 1;
                 t->blocked = 1;
+                smp_mb();
                 if (waitqueue_active(&root->fs_info->transaction_blocked_wait))
                         wake_up(&root->fs_info->transaction_blocked_wait);
 
                 t->blocked = 0;
+                smp_mb();
                 if (waitqueue_active(&root->fs_info->transaction_wait))
                         wake_up(&root->fs_info->transaction_wait);
 
                 t->commit_done = 1;
+                smp_mb();
                 if (waitqueue_active(&t->commit_wait))
                         wake_up(&t->commit_wait);
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2d65c52b0944..97baf00b40d1 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1007,9 +1007,7 @@ static noinline void async_cow_submit(struct btrfs_work *work)
         nr_pages = (async_cow->end - async_cow->start + PAGE_CACHE_SIZE) >>
                 PAGE_CACHE_SHIFT;
 
-        atomic_sub(nr_pages, &root->fs_info->async_delalloc_pages);
-
-        if (atomic_read(&root->fs_info->async_delalloc_pages) <
+        if (atomic_sub_return(nr_pages, &root->fs_info->async_delalloc_pages) <
             5 * 1024 * 1024 &&
             waitqueue_active(&root->fs_info->async_submit_wait))
                 wake_up(&root->fs_info->async_submit_wait);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3b394503bd4e..0b1e69d380dd 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -227,9 +227,8 @@ loop_lock:
                 cur = pending;
                 pending = pending->bi_next;
                 cur->bi_next = NULL;
-                atomic_dec(&fs_info->nr_async_bios);
 
-                if (atomic_read(&fs_info->nr_async_bios) < limit &&
+                if (atomic_dec_return(&fs_info->nr_async_bios) < limit &&
                     waitqueue_active(&fs_info->async_submit_wait))
                         wake_up(&fs_info->async_submit_wait);