From: Charan Teja Kalla Date: Thu, 14 Dec 2023 04:58:41 +0000 (+0000) Subject: mm: migrate high-order folios in swap cache correctly X-Git-Tag: v6.6.14~871 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=07550b1461d4d0499165e7d6f7718cfd0e440427;p=platform%2Fkernel%2Flinux-starfive.git mm: migrate high-order folios in swap cache correctly commit fc346d0a70a13d52fe1c4bc49516d83a42cd7c4c upstream. Large folios occupy N consecutive entries in the swap cache instead of using multi-index entries like the page cache. However, if a large folio is re-added to the LRU list, it can be migrated. The migration code was not aware of the difference between the swap cache and the page cache and assumed that a single xas_store() would be sufficient. This leaves potentially many stale pointers to the now-migrated folio in the swap cache, which can lead to almost arbitrary data corruption in the future. This can also manifest as infinite loops with the RCU read lock held. [willy@infradead.org: modifications to the changelog & tweaked the fix] Fixes: 3417013e0d18 ("mm/migrate: Add folio_migrate_mapping()") Link: https://lkml.kernel.org/r/20231214045841.961776-1-willy@infradead.org Signed-off-by: Charan Teja Kalla Signed-off-by: Matthew Wilcox (Oracle) Reported-by: Charan Teja Kalla Closes: https://lkml.kernel.org/r/1700569840-17327-1-git-send-email-quic_charante@quicinc.com Cc: David Hildenbrand Cc: Johannes Weiner Cc: Kirill A. Shutemov Cc: Naoya Horiguchi Cc: Shakeel Butt Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- diff --git a/mm/migrate.c b/mm/migrate.c index 06086dc..03bc206 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -405,6 +405,7 @@ int folio_migrate_mapping(struct address_space *mapping, int dirty; int expected_count = folio_expected_refs(mapping, folio) + extra_count; long nr = folio_nr_pages(folio); + long entries, i; if (!mapping) { /* Anonymous page without mapping */ @@ -442,8 +443,10 @@ int folio_migrate_mapping(struct address_space *mapping, folio_set_swapcache(newfolio); newfolio->private = folio_get_private(folio); } + entries = nr; } else { VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio); + entries = 1; } /* Move dirty while page refs frozen and newpage not yet exposed */ @@ -453,7 +456,11 @@ int folio_migrate_mapping(struct address_space *mapping, folio_set_dirty(newfolio); } - xas_store(&xas, newfolio); + /* Swap cache still stores N entries instead of a high-order entry */ + for (i = 0; i < entries; i++) { + xas_store(&xas, newfolio); + xas_next(&xas); + } /* * Drop cache reference from old page by unfreezing