[PATCH 7.1 18/21] drivers/base/memory: set mem->altmap after successful device registration

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Georgi Djakov <georgi.djakov@oss.qualcomm.com>

commit a2b8d7827f48ee54a686cb80e4a1d0ff954ec42a upstream.

If __add_memory_block() fails at xa_store() (under memory pressure for
example), device_unregister() is called, which eventually triggers
memory_block_release() with mem->altmap still set, causing a
WARN_ON(mem->altmap).  This was triggered by modifying virtio-mem driver.

Fix this by delaying the assignment of mem->altmap until after
__add_memory_block() has succeeded.

Link: https://lore.kernel.org/20260514092657.3057141-1-georgi.djakov@oss.qualcomm.com
Fixes: 1a8c64e11043 ("mm/memory_hotplug: embed vmem_altmap details in memory block")
Signed-off-by: Georgi Djakov <georgi.djakov@oss.qualcomm.com>
Acked-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Richard Cheng <icheng@nvidia.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Georgi Djakov <djakov@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/base/memory.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -807,7 +807,6 @@ static int add_memory_block(unsigned lon
 	mem->start_section_nr = block_id * sections_per_block;
 	mem->state = state;
 	mem->nid = nid;
-	mem->altmap = altmap;
 	INIT_LIST_HEAD(&mem->group_next);
 
 #ifndef CONFIG_NUMA
@@ -825,6 +824,8 @@ static int add_memory_block(unsigned lon
 	if (ret)
 		return ret;
 
+	mem->altmap = altmap;
+
 	if (group) {
 		mem->group = group;
 		list_add(&mem->group_next, &group->memory_blocks);