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mm/thp: fix deferred split queue not partially_mapped: fix

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Though even more elusive than before, list_del corruption has still been
seen on THP's deferred split queue.

The idea in commit e66f3185fa was right, but its implementation wrong. 
The context omitted an important comment just before the critical test:
"split_folio() removes folio from list on success." In ignoring that
comment, when a THP split succeeded, the code went on to release the
preceding safe folio, preserving instead an irrelevant (formerly head)
folio: which gives no safety because it's not on the list.  Fix the logic.

Link: https://lkml.kernel.org/r/3c995a30-31ce-0998-1b9f-3a2cb9354c91@google.com
Fixes: e66f3185fa ("mm/thp: fix deferred split queue not partially_mapped")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Usama Arif <usamaarif642@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2024-11-10 13:11:21 -08:00 committed by Andrew Morton
parent 94efde1d15
commit a3477c9e02
1 changed files with 3 additions and 1 deletions
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4
mm/huge_memory.c
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@ -3790,7 +3790,9 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
* in the case it was underused, then consider it used and
* don't add it back to split_queue.
*/
if (!did_split && !folio_test_partially_mapped(folio)) {
if (did_split) {
; /* folio already removed from list */
} else if (!folio_test_partially_mapped(folio)) {
list_del_init(&folio->_deferred_list);
removed++;
} else {