writeback: remove broken rbtree_postorder_for_each_entry_safe() usage in cgwb_bdi_destroy() (e27c5b9d) · Commits · 戴 / test

("writeback: don't drain bdi_writeback_congested on bdi destruction") added rbtree_postorder_for_each_entry_safe() which is used to remove all entries; however, according to Cody, the iterator isn't safe against operations which may rebalance the tree. Fix it by switching to repeatedly removing rb_first() until empty. Signed-off-by:

Tejun Heo <tj@kernel.org> Reported-by:

Cody P Schafer <dev@codyps.com> Fixes: ("writeback: don't drain bdi_writeback_congested on bdi destruction") Link: http://lkml.kernel.org/g/1443997973-1700-1-git-send-email-dev@codyps.com Signed-off-by:

Jens Axboe <axboe@fb.com>

mm/backing-dev.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -681,7 +681,7 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi)
		static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
		{
		struct radix_tree_iter iter;
		struct bdi_writeback_congested congested, congested_n;
		struct rb_node *rbn;
		void **slot;

		WARN_ON(test_bit(WB_registered, &bdi->wb.state));
		@@ -691,9 +691,11 @@ static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
		radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
		cgwb_kill(*slot);

		rbtree_postorder_for_each_entry_safe(congested, congested_n,
		&bdi->cgwb_congested_tree, rb_node) {
		rb_erase(&congested->rb_node, &bdi->cgwb_congested_tree);
		while ((rbn = rb_first(&bdi->cgwb_congested_tree))) {
		struct bdi_writeback_congested *congested =
		rb_entry(rbn, struct bdi_writeback_congested, rb_node);

		rb_erase(rbn, &bdi->cgwb_congested_tree);
		congested->bdi = NULL; /* mark @congested unlinked */
		}

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