The patch titled
Subject: mm: migrate high-order folios in swap cache correctly
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-migrate-high-order-folios-in-swap-cache-correctly.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-high-order-folios-in-swap-cache-correctly.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Subject: mm: migrate high-order folios in swap cache correctly
Date: Thu, 14 Dec 2023 04:58:41 +0000
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@xxxxxxxxxxxxx: modifications to the changelog & tweaked the fix]
Fixes: 3417013e0d183be ("mm/migrate: Add folio_migrate_mapping()")
Link: https://lkml.kernel.org/r/20231214045841.961776-1-willy@xxxxxxxxxxxxx
Signed-off-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reported-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Closes: https://lkml.kernel.org/r/1700569840-17327-1-git-send-email-quic_charante@xxxxxxxxxxx
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/mm/migrate.c~mm-migrate-high-order-folios-in-swap-cache-correctly
+++ a/mm/migrate.c
@@ -405,6 +405,7 @@ int folio_migrate_mapping(struct address
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
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
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
_
Patches currently in -mm which might be from quic_charante@xxxxxxxxxxx are
mm-sparsemem-fix-race-in-accessing-memory_section-usage.patch
mm-sparsemem-fix-race-in-accessing-memory_section-usage-v2.patch
mm-migrate-high-order-folios-in-swap-cache-correctly.patch
