jbd2: fix a race when checking checkpoint buffer busy

[mirror_ubuntu-kernels.git] / fs / jbd2 / checkpoint.c

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 42b34cab64fbdb46b8b6410902ad8349cbeb9e66..9ec91017a7f3ca12e43c4ce7452a56509a66c814 100644 (file)
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -376,11 +376,15 @@ static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
                jh = next_jh;
                next_jh = jh->b_cpnext;
 
-               if (!destroy && __cp_buffer_busy(jh))
-                       continue;
+               if (destroy) {
+                       ret = __jbd2_journal_remove_checkpoint(jh);
+               } else {
+                       ret = jbd2_journal_try_remove_checkpoint(jh);
+                       if (ret < 0)
+                               continue;
+               }
 
                nr_freed++;
-               ret = __jbd2_journal_remove_checkpoint(jh);
                if (ret) {
                        *released = true;
                        break;
@@ -616,6 +620,34 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
        return 1;
 }
 
+/*
+ * Check the checkpoint buffer and try to remove it from the checkpoint
+ * list if it's clean. Returns -EBUSY if it is not clean, returns 1 if
+ * it frees the transaction, 0 otherwise.
+ *
+ * This function is called with j_list_lock held.
+ */
+int jbd2_journal_try_remove_checkpoint(struct journal_head *jh)
+{
+       struct buffer_head *bh = jh2bh(jh);
+
+       if (!trylock_buffer(bh))
+               return -EBUSY;
+       if (buffer_dirty(bh)) {
+               unlock_buffer(bh);
+               return -EBUSY;
+       }
+       unlock_buffer(bh);
+
+       /*
+        * Buffer is clean and the IO has finished (we held the buffer
+        * lock) so the checkpoint is done. We can safely remove the
+        * buffer from this transaction.
+        */
+       JBUFFER_TRACE(jh, "remove from checkpoint list");
+       return __jbd2_journal_remove_checkpoint(jh);
+}
+
 /*
  * journal_insert_checkpoint: put a committed buffer onto a checkpoint
  * list so that we know when it is safe to clean the transaction out of