Btrfs: protect conditions within root->log_mutex while waiting

Both wait_for_commit() and wait_for_writer() are checking the
condition out of the mutex lock.

This refactors code a bit to be lock safe.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 16 insertions, 14 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index c800d067fcbf..963f22b17508 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2699,34 +2699,36 @@ static void wait_log_commit(struct btrfs_root *root, int transid)
          * so we know that if ours is more than 2 older than the
          * current transaction, we're done
          */
-        do {
+        for (;;) {
                 prepare_to_wait(&root->log_commit_wait[index],
                                 &wait, TASK_UNINTERRUPTIBLE);
-                mutex_unlock(&root->log_mutex);
 
-                if (root->log_transid_committed < transid &&
-                    atomic_read(&root->log_commit[index]))
-                        schedule();
+                if (!(root->log_transid_committed < transid &&
+                      atomic_read(&root->log_commit[index])))
+                        break;
 
-                finish_wait(&root->log_commit_wait[index], &wait);
+                mutex_unlock(&root->log_mutex);
+                schedule();
                 mutex_lock(&root->log_mutex);
-        } while (root->log_transid_committed < transid &&
-                 atomic_read(&root->log_commit[index]));
+        }
+        finish_wait(&root->log_commit_wait[index], &wait);
 }
 
 static void wait_for_writer(struct btrfs_root *root)
 {
         DEFINE_WAIT(wait);
 
-        while (atomic_read(&root->log_writers)) {
-                prepare_to_wait(&root->log_writer_wait,
-                                &wait, TASK_UNINTERRUPTIBLE);
+        for (;;) {
+                prepare_to_wait(&root->log_writer_wait, &wait,
+                                TASK_UNINTERRUPTIBLE);
+                if (!atomic_read(&root->log_writers))
+                        break;
+
                 mutex_unlock(&root->log_mutex);
-                if (atomic_read(&root->log_writers))
-                        schedule();
-                finish_wait(&root->log_writer_wait, &wait);
+                schedule();
                 mutex_lock(&root->log_mutex);
         }
+        finish_wait(&root->log_writer_wait, &wait);
 }
 
 static inline void btrfs_remove_log_ctx(struct btrfs_root *root,