I'm testing UFS with SU+J. But it seems sometimes broken journal data has 

In softdep_process_journal (ffs_softdep.c), there is a while code to build 
jsegrec and each entry.
But by my test, sometimes there is no entry then break this while code without 
building jsegrec.
If this happens, bp->b_data is not initialized but this bp is written, I think.

I checked this behavior by following patch.
diff --git a/sys/ufs/ffs/ffs_softdep.c b/sys/ufs/ffs/ffs_softdep.c
index 585af50..2d4939c 100644
--- a/sys/ufs/ffs/ffs_softdep.c
+++ b/sys/ufs/ffs/ffs_softdep.c
@@ -3421,6 +3421,15 @@ softdep_process_journal(mp, needwk, flags)
                        data = bp->b_data + off;
+#if 1
+               if (off == 0) {
+                       struct jsegrec *tmp = (struct jsegrec*)bp->b_data;
+                       if (tmp->jsr_seq != jseg->js_seq) {
+                               panic("test test");
+                       }
+               }
                 * Write this one buffer and continue.

If uninitialized data is "valid" by fsck suj, this may result filesystem 
corruption, I think.
I think it's better to clear b_data before using it.

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