From: Dev Jain Date: Wed, 4 Jun 2025 04:15:33 +0000 (+0530) Subject: xarray: add a BUG_ON() to ensure caller is not sibling X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1e6b17b4237dacb02e9cfeaed35d889bbc9e8a84;p=thirdparty%2Fkernel%2Flinux.git xarray: add a BUG_ON() to ensure caller is not sibling Suppose xas is pointing somewhere near the end of the multi-entry batch. Then it may happen that the computed slot already falls beyond the batch, thus breaking the loop due to !xa_is_sibling(), and computing the wrong order. For example, suppose we have a shift-6 node having an order-9 entry => 8 - 1 = 7 siblings, so assume the slots are at offset 0 till 7 in this node. If xas->xa_offset is 6, then the code will compute order as 1 + xas->xa_node->shift = 7. Therefore, the order computation must start from the beginning of the multi-slot entries, that is, the non-sibling entry. Thus ensure that the caller is aware of this by triggering a BUG when the entry is a sibling entry. Note that this BUG_ON() is only active while running selftests, so there is no overhead in a running kernel. Link: https://lkml.kernel.org/r/20250604041533.91198-1-dev.jain@arm.com Signed-off-by: Dev Jain Acked-by: Zi Yan Cc: "Aneesh Kumar K.V" Cc: Anshuman Khandual Cc: David Hildenbrand Cc: Matthew Wilcox (Oracle) Cc: Ryan Roberts Signed-off-by: Andrew Morton --- diff --git a/lib/xarray.c b/lib/xarray.c index 76dde3a1cacf5..ae3d80f4b4ee3 100644 --- a/lib/xarray.c +++ b/lib/xarray.c @@ -1910,6 +1910,7 @@ EXPORT_SYMBOL(xa_store_range); * @xas: XArray operation state. * * Called after xas_load, the xas should not be in an error state. + * The xas should not be pointing to a sibling entry. * * Return: A number between 0 and 63 indicating the order of the entry. */ @@ -1920,6 +1921,8 @@ int xas_get_order(struct xa_state *xas) if (!xas->xa_node) return 0; + XA_NODE_BUG_ON(xas->xa_node, xa_is_sibling(xa_entry(xas->xa, + xas->xa_node, xas->xa_offset))); for (;;) { unsigned int slot = xas->xa_offset + (1 << order);