btrfs: Fix bugs in zlib workspace

- Fix a race that can result in alloc_workspace > cpus.
- Fix to check num_workspace after wakeup.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
index b9cd5445f71c..e5b8b22e07d6 100644
--- a/fs/btrfs/zlib.c
+++ b/fs/btrfs/zlib.c
@@ -75,16 +75,19 @@ again:
                 return workspace;
 
         }
-        spin_unlock(&workspace_lock);
         if (atomic_read(&alloc_workspace) > cpus) {
                 DEFINE_WAIT(wait);
+
+                spin_unlock(&workspace_lock);
                 prepare_to_wait(&workspace_wait, &wait, TASK_UNINTERRUPTIBLE);
-                if (atomic_read(&alloc_workspace) > cpus)
+                if (atomic_read(&alloc_workspace) > cpus && !num_workspace)
                         schedule();
                 finish_wait(&workspace_wait, &wait);
                 goto again;
         }
         atomic_inc(&alloc_workspace);
+        spin_unlock(&workspace_lock);
+
         workspace = kzalloc(sizeof(*workspace), GFP_NOFS);
         if (!workspace) {
                 ret = -ENOMEM;