f2fs: disable f2fs_check_rb_tree_consistence

If there is millions of discard entries cached in rb tree, each
sanity check of it can cause very long latency as held cmd_lock
blocking other lock grabbers.

In other aspect, we have enabled the check very long time, as
we see, there is no such inconsistent condition caused by bugs.

But still we do not choose to kill it directly, instead, adding
an flag to disable the check now, if there is related code change,
we can reuse it to detect bugs.
Signed-off-by: Yunlei He <heyunlei@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -311,6 +311,7 @@ struct discard_cmd_control {
 	atomic_t issing_discard;		/* # of issing discard */
 	atomic_t discard_cmd_cnt;		/* # of cached cmd count */
 	struct rb_root root;			/* root of discard rb-tree */
+	bool rbtree_check;			/* config for consistence check */
 };
 
 /* for the list of fsync inodes, used only during recovery */

fs/f2fs/segment.c

@@ -1199,8 +1199,9 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 		mutex_lock(&dcc->cmd_lock);
 		if (list_empty(pend_list))
 			goto next;
-		f2fs_bug_on(sbi,
-			!f2fs_check_rb_tree_consistence(sbi, &dcc->root));
+		if (unlikely(dcc->rbtree_check))
+			f2fs_bug_on(sbi, !f2fs_check_rb_tree_consistence(sbi,
+								&dcc->root));
 		blk_start_plug(&plug);
 		list_for_each_entry_safe(dc, tmp, pend_list, list) {
 			f2fs_bug_on(sbi, dc->state != D_PREP);
@@ -1752,6 +1753,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
 	dcc->max_discards = MAIN_SEGS(sbi) << sbi->log_blocks_per_seg;
 	dcc->undiscard_blks = 0;
 	dcc->root = RB_ROOT;
+	dcc->rbtree_check = false;
 
 	init_waitqueue_head(&dcc->discard_wait_queue);
 	SM_I(sbi)->dcc_info = dcc;
@@ -2381,7 +2383,9 @@ static void __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
 	issued = 0;
 
 	mutex_lock(&dcc->cmd_lock);
-	f2fs_bug_on(sbi, !f2fs_check_rb_tree_consistence(sbi, &dcc->root));
+	if (unlikely(dcc->rbtree_check))
+		f2fs_bug_on(sbi, !f2fs_check_rb_tree_consistence(sbi,
+								&dcc->root));
 
 	dc = (struct discard_cmd *)f2fs_lookup_rb_tree_ret(&dcc->root,
 					NULL, start,