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mm: migrate high-order folios in swap cache correctly

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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: 3417013e0d ("mm/migrate: Add folio_migrate_mapping()")
Link: https://lkml.kernel.org/r/20231214045841.961776-1-willy@infradead.org
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reported-by: Charan Teja Kalla <quic_charante@quicinc.com>
Closes: https://lkml.kernel.org/r/1700569840-17327-1-git-send-email-quic_charante@quicinc.com
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Charan Teja Kalla 2023-12-14 04:58:41 +00:00 committed by Andrew Morton
parent 4249f13c11
commit fc346d0a70
1 changed files with 8 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

7
mm/migrate.c
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@ -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);
}
/* 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