1 files changed, 21 insertions, 5 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 8bb013672aee..855935f6671a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4986,24 +4986,40 @@ static void evict_inode_truncate_pages(struct inode *inode)
 	}
 	write_unlock(&map_tree->lock);
 
+	/*
+	 * Keep looping until we have no more ranges in the io tree.
+	 * We can have ongoing bios started by readpages (called from readahead)
+	 * that didn't get their end io callbacks called yet or they are still
+	 * in progress ((extent_io.c:end_bio_extent_readpage()). This means some
+	 * ranges can still be locked and eviction started because before
+	 * submitting those bios, which are executed by a separate task (work
+	 * queue kthread), inode references (inode->i_count) were not taken
+	 * (which would be dropped in the end io callback of each bio).
+	 * Therefore here we effectively end up waiting for those bios and
+	 * anyone else holding locked ranges without having bumped the inode's
+	 * reference count - if we don't do it, when they access the inode's
+	 * io_tree to unlock a range it may be too late, leading to an
+	 * use-after-free issue.
+	 */
 	spin_lock(&io_tree->lock);
 	while (!RB_EMPTY_ROOT(&io_tree->state)) {
 		struct extent_state *state;
 		struct extent_state *cached_state = NULL;
+		u64 start;
+		u64 end;
 
 		node = rb_first(&io_tree->state);
 		state = rb_entry(node, struct extent_state, rb_node);
-		atomic_inc(&state->refs);
+		start = state->start;
+		end = state->end;
 		spin_unlock(&io_tree->lock);
 
-		lock_extent_bits(io_tree, state->start, state->end,
-				 0, &cached_state);
-		clear_extent_bit(io_tree, state->start, state->end,
+		lock_extent_bits(io_tree, start, end, 0, &cached_state);
+		clear_extent_bit(io_tree, start, end,
 				 EXTENT_LOCKED | EXTENT_DIRTY |
 				 EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING |
 				 EXTENT_DEFRAG, 1, 1,
 				 &cached_state, GFP_NOFS);
-		free_extent_state(state);
 
 		cond_resched();
 		spin_lock(&io_tree->lock);