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X-CSE-ConnectionGUID: x9Uq9XBjQa23OvTpSWGAeg== X-CSE-MsgGUID: Olp7m8JTT/SvHLhmb65bnQ== X-IronPort-AV: E=McAfee;i="6800,10657,11866"; a="90376833" X-IronPort-AV: E=Sophos;i="6.25,207,1779174000"; d="scan'208";a="90376833" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by fmvoesa106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2026 16:10:49 -0700 X-CSE-ConnectionGUID: gdzBu8tUSsWVVT+WYsw11w== X-CSE-MsgGUID: Douz6uonSw2oqZmSx0TiGg== X-ExtLoop1: 1 Received: from gsse-cloud1.jf.intel.com ([10.54.39.91]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2026 16:10:48 -0700 From: Matthew Brost To: intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Arvind Yadav , Andrew Morton , David Hildenbrand , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Zi Yan , Balbir Singh Subject: [PATCH v3 1/6] mm/migrate_device: Clear stale mapping after freeing swapcache Date: Wed, 5 Aug 2026 16:10:36 -0700 Message-Id: <20260805231041.3791771-2-matthew.brost@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260805231041.3791771-1-matthew.brost@intel.com> References: <20260805231041.3791771-1-matthew.brost@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5A3CEC000D X-Stat-Signature: gbny4i98kibq9dcwuf15a1foztmz97g6 X-Rspam-User: X-HE-Tag: 1785971451-612809 X-HE-Meta: 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 CCB6I1P/ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Arvind Yadav __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. v2: - Refresh the mapping using folio_mapping(), as suggested by Zi Yan. v3: - Reset nr to 1 after a successful split so each resulting folio is processed independently, as suggested by Zi Yan. v4: - Re-read each source folio's mapping immediately before folio_migrate_mapping(), as suggested by Balbir Singh. - Add a warning to validate the post-split order-0 invariant, as suggested by Balbir Singh. Fixes: df263d9a7dff ("mm/migrate_device: try to handle swapcache pages") Cc: Andrew Morton Cc: David Hildenbrand Cc: Matthew Brost Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Reviewed-by: Zi Yan Reviewed-by: Balbir Singh Signed-off-by: Arvind Yadav --- mm/migrate_device.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 908d2d4ec43a..162d29b2807a 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -1183,6 +1183,13 @@ static void __migrate_device_pages(unsigned long *src_pfns, 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)) { @@ -1222,6 +1229,12 @@ static void __migrate_device_pages(unsigned long *src_pfns, 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; -- 2.34.1