[PATCH bpf-next v2 3/3] bpf, arena: check range_tree_set return in arena_free_pages and arena_free_worker

From: Yuan Chen <[email protected]>

arena_free_pages() and arena_free_worker() now handle range_tree_set()
errors. arena_free_pages() aborts the free on error, and
arena_free_worker() moves range_tree_set() before PTE clearing so that a
failed tree update leaves the PTEs intact instead of freeing pages that
the arena free tree does not track.

Signed-off-by: Yuan Chen <[email protected]>
---
 kernel/bpf/arena.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
index 555ee2531ef9..b374ebf2a4de 100644
--- a/kernel/bpf/arena.c
+++ b/kernel/bpf/arena.c
@@ -881,7 +881,12 @@ static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt,
 	if (ret)
 		goto defer;
 
-	range_tree_set(&arena->rt, pgoff, page_cnt);
+	ret = range_tree_set(&arena->rt, pgoff, page_cnt);
+	if (ret) {
+		raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
+		bpf_map_memcg_exit(old_memcg, new_memcg);
+		return;
+	}
 
 	init_llist_head(&free_pages);
 	cdata.arena = arena;
@@ -1004,11 +1009,18 @@ static void arena_free_worker(struct work_struct *work)
 		kaddr = arena_vm_start + s->uaddr;
 		pgoff = compute_pgoff(arena, s->uaddr);
 
+		/*
+		 * Mark the range as free before clearing PTEs so that
+		 * if the range tree update fails we leave the PTEs
+		 * intact, avoiding an unrecoverable state where pages
+		 * are freed but the arena free tree does not track them.
+		 */
+		if (range_tree_set(&arena->rt, pgoff, page_cnt))
+			continue;
+
 		/* clear ptes and collect pages in free_pages llist */
 		apply_to_existing_page_range(&init_mm, kaddr, page_cnt << PAGE_SHIFT,
 					     apply_range_clear_cb, &cdata);
-
-		range_tree_set(&arena->rt, pgoff, page_cnt);
 	}
 	raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
 
-- 
2.54.0