FAILED: patch "[PATCH] drivers/base/memory: set mem->altmap after successful device" failed to apply to 6.12-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x a2b8d7827f48ee54a686cb80e4a1d0ff954ec42a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026062556-emcee-reexamine-cc0e@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a2b8d7827f48ee54a686cb80e4a1d0ff954ec42a Mon Sep 17 00:00:00 2001
From: Georgi Djakov <georgi.djakov@oss.qualcomm.com>
Date: Thu, 14 May 2026 02:26:57 -0700
Subject: [PATCH] drivers/base/memory: set mem->altmap after successful device
 registration

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>

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index d31a421f7483..b318344426fa 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -797,7 +797,6 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
 	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
@@ -815,6 +814,8 @@ static int add_memory_block(unsigned long block_id, int nid, unsigned long state
 	if (ret)
 		return ret;
 
+	mem->altmap = altmap;
+
 	if (group) {
 		mem->group = group;
 		list_add(&mem->group_next, &group->memory_blocks);