[merged mm-stable] mm-migrate_device-clear-stale-mapping-after-freeing-swapcache.patch removed from -mm tree

[merged mm-stable] mm-migrate_device-clear-stale-mapping-after-freeing-swapcache.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/migrate_device: clear stale mapping after freeing swapcache
has been removed from the -mm tree.  Its filename was
     mm-migrate_device-clear-stale-mapping-after-freeing-swapcache.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Arvind Yadav <arvind.yadav@intel.com>
Subject: mm/migrate_device: clear stale mapping after freeing swapcache
Date: Tue, 28 Jul 2026 11:58:32 +0530

__migrate_device_pages() reads the folio mapping before calling
folio_free_swap().  When folio_free_swap() succeeds, the folio is removed
from the swap cache, but the saved mapping still points to swap_space.

Passing the stale mapping to folio_migrate_mapping() makes it use the
mapped-folio path for a folio that is no longer in swapcache.  It can then
operate on swap_space.i_pages with invalid reference accounting,
eventually triggering a folio reference count BUG.

After a successful split, nr still contains the number of pages in the
original large folio, although each resulting page is now a separate
order-0 folio.  Reset nr to 1 so each split folio is processed separately,
including its own swapcache removal and mapping lookup.

Refresh the saved mapping after folio_free_swap() so the current folio
state is used during migration.

Link: https://lore.kernel.org/20260728062832.1107127-1-arvind.yadav@intel.com
Fixes: df263d9a7dff ("mm/migrate_device: try to handle swapcache pages")
Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Balbir Singh <balbirs@nvidia.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/migrate_device.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/mm/migrate_device.c~mm-migrate_device-clear-stale-mapping-after-freeing-swapcache
+++ a/mm/migrate_device.c
@@ -1193,6 +1193,13 @@ static void __migrate_device_pages(unsig
 							 MIGRATE_PFN_COMPOUND);
 					goto next;
 				}
+
+				/*
+				 * reset nr so that only first after-split folio
+				 * is processed below
+				 */
+				VM_WARN_ON_ONCE(folio_test_large(folio));
+				nr = 1;
 			} else if ((src_pfns[i] & MIGRATE_PFN_MIGRATE) &&
 				(dst_pfns[i] & MIGRATE_PFN_COMPOUND) &&
 				!(src_pfns[i] & MIGRATE_PFN_COMPOUND)) {
@@ -1232,6 +1239,12 @@ static void __migrate_device_pages(unsig
 			folio = page_folio(migrate_pfn_to_page(src_pfns[i+j]));
 			newfolio = page_folio(migrate_pfn_to_page(dst_pfns[i+j]));
 
+			/*
+			 * folio_free_swap() removed the folio from the swap
+			 * cache. Refresh the saved mapping before migration.
+			 */
+			mapping = folio_mapping(folio);
+
 			r = folio_migrate_mapping(mapping, newfolio, folio, extra_cnt);
 			if (r)
 				src_pfns[i+j] &= ~MIGRATE_PFN_MIGRATE;
_

Patches currently in -mm which might be from arvind.yadav@intel.com are