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[PATCH v2] mm/migrate_device: Clear stale mapping after freeing swapcache To: Arvind Yadav , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, david@kernel.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, ziy@nvidia.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com References: <20260724082702.2531024-1-arvind.yadav@intel.com> Content-Language: en-US From: Balbir Singh In-Reply-To: <20260724082702.2531024-1-arvind.yadav@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MEWPR01CA0231.ausprd01.prod.outlook.com (2603:10c6:220:1ea::17) To CH2PR12MB5001.namprd12.prod.outlook.com (2603:10b6:610:61::18) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB5001:EE_|IA1PR12MB6233:EE_ X-MS-Office365-Filtering-Correlation-Id: 17ccc031-c599-45ea-9532-08deeb8c11e1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 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Arvind Yadav wrote: > __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 take the > mapped-folio path after the swapcache reference has been dropped. This can > cause an invalid swap_space lock access followed by a folio reference > count BUG. > > Refresh the saved mapping after folio_free_swap() so the current folio > state is used during migration. > > v2: > - Refresh the mapping using folio_mapping(), as suggested by Zi Yan. > > Fixes: df263d9a7dff ("mm/migrate_device: try to handle swapcache pages") > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Matthew Brost > Cc: Joshua Hahn > Cc: Zi Yan > Cc: Rakie Kim > Cc: Byungchul Park > Cc: Gregory Price > Cc: Ying Huang > Cc: Alistair Popple > Signed-off-by: Arvind Yadav > --- > mm/migrate_device.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 554754eb26ff..ae895758b72c 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -1204,6 +1204,12 @@ static void __migrate_device_pages(unsigned long *src_pfns, > src_pfns[i] &= ~MIGRATE_PFN_MIGRATE; > goto next; > } > + > + /* > + * folio_free_swap() removed the folio from the swap > + * cache. Refresh the saved mapping before migration. > + */ > + mapping = folio_mapping(folio); > } > } else if (folio_is_zone_device(newfolio)) { > /* LGTM Reviewed-by: Balbir Singh