[PATCH 2/4] of: reserved_mem: keep the reservation when node_init returns -EBUSY

[Radhey Shyam Pandey]

fdt_init_reserved_mem_node() treats any error from a region's init function
as "this node is unusable" and calls memblock_phys_free() on the whole
range, although the range was reserved earlier during the FDT scan by code
unrelated to that init function. Give -EBUSY the meaning "cannot be used as
described, but must stay reserved" and skip the release for it. Nothing
returns -EBUSY from node_init today. The next patch does, to refuse a CMA
pool overlapping the kernel image, which without this would free
[_text, _end) rather than protect it.

Suggested-by: Pratyush Yadav (Google) <pratyush@xxxxxxxxxx>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxx>
---
Changes since RFC:
- New patch
---
 drivers/of/of_reserved_mem.c    | 14 ++++++++++++++
 include/linux/of_reserved_mem.h |  5 +++++
 2 files changed, 19 insertions(+)

diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index 0fd1683cba01..d67a2b3a4d44 100644
--- a/drivers/of/of_reserved_mem.c
+++ b/drivers/of/of_reserved_mem.c
@@ -621,6 +621,20 @@ static void __init fdt_init_reserved_mem_node(unsigned long node, const char *un
 
 	err = __reserved_mem_init_node(rmem, node);
 	if (err != 0 && err != -ENODEV) {
+		/*
+		 * The region was reserved before its init function ran, so it
+		 * is not ours to release. -EBUSY says the init function is
+		 * declining it for a reason that outlives this node; freeing
+		 * it would hand the range to the page allocator even though
+		 * something else still owns it.
+		 */
+		if (err == -EBUSY) {
+			pr_info("node %s init failed, keeping reservation\n",
+				rmem->name);
+			rmem->name = NULL;
+			return;
+		}
+
 		pr_info("node %s compatible matching fail\n", rmem->name);
 		rmem->name = NULL;
 
diff --git a/include/linux/of_reserved_mem.h b/include/linux/of_reserved_mem.h
index 49da515859f2..4bf32f80785c 100644
--- a/include/linux/of_reserved_mem.h
+++ b/include/linux/of_reserved_mem.h
@@ -21,6 +21,11 @@ struct reserved_mem_ops {
 	int	(*node_validate)(unsigned long fdt_node, phys_addr_t *align);
 	int	(*node_fixup)(unsigned long fdt_node, phys_addr_t base,
 			      phys_addr_t size);
+	/*
+	 * Returns 0 on success, -ENODEV if the node is not handled by these
+	 * ops, or -EBUSY if the region cannot be used but must stay reserved.
+	 * Any other error releases the region.
+	 */
 	int	(*node_init)(unsigned long fdt_node, struct reserved_mem *rmem);
 	int	(*device_init)(struct reserved_mem *rmem,
 			       struct device *dev);
-- 
2.44.4