[PATCH 5/6] btrfs: handle -EAGAIN from btrfs_duplicate_item and refresh stale leaf pointer

[robbieko <robbieko@synology.com>]

In the 'punch a hole' case of btrfs_delete_raid_extent(),
btrfs_duplicate_item() can return -EAGAIN when the leaf needs to be
split and the path becomes invalid. The old code treats any error as
fatal and breaks out of the loop.

Additionally, btrfs_duplicate_item() may trigger setup_leaf_for_split()
which can reallocate the leaf node. The code continues using the old
leaf pointer, leading to use-after-free or stale data access.

Fix both issues by:
- Handling -EAGAIN specifically: release the path and retry the loop.
- Refreshing leaf = path->nodes[0] after successful duplication.

Signed-off-by: robbieko <robbieko@synology.com>
---
 fs/btrfs/raid-stripe-tree.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/btrfs/raid-stripe-tree.c b/fs/btrfs/raid-stripe-tree.c
index 5909ad35a1b0..1e8392a6c5a4 100644
--- a/fs/btrfs/raid-stripe-tree.c
+++ b/fs/btrfs/raid-stripe-tree.c
@@ -194,9 +194,19 @@ int btrfs_delete_raid_extent(struct btrfs_trans_handle *trans, u64 start, u64 le
 
 			/* The "right" item. */
 			ret = btrfs_duplicate_item(trans, stripe_root, path, &newkey);
+			if (ret == -EAGAIN) {
+				btrfs_release_path(path);
+				continue;
+			}
 			if (ret)
 				break;
 
+			/*
+			 * btrfs_duplicate_item() may have triggered a leaf
+			 * split via setup_leaf_for_split(), so we must refresh
+			 * our leaf pointer from the path.
+			 */
+			leaf = path->nodes[0];
 			item_size = btrfs_item_size(leaf, path->slots[0]);
 			extent = btrfs_item_ptr(leaf, path->slots[0],
 						struct btrfs_stripe_extent);
-- 
2.43.0


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