+ * Bug Issue Id: #7512
+ * The bug time sequence:
+ * 1. context #1, zfs_write assign a txg "n".
+ * 2. In the same process, context #2, mmap page fault (which means the mm_sem
+ * is hold) occurred, zfs_dirty_inode open a txg failed, and wait previous
+ * txg "n" completed.
+ * 3. context #1 call uiomove to write, however page fault is occurred in
+ * uiomove, which means it need mm_sem, but mm_sem is hold by
+ * context #2, so it stuck and can't complete, then txg "n" will not
+ * complete.