[PATCH] Btrfs: protect conditions within root->log_mutex while waiting

[Liu Bo]

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....@oracle.com>
---
 fs/btrfs/tree-log.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 3a11ae6..434dcd5 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2701,34 +2701,36 @@ 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,
-- 
2.9.4

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