From: SeongJae Park Date: Mon, 25 May 2026 16:22:55 +0000 (-0700) Subject: mm/damon/ops-common: call folio_test_lru() after folio_get() X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef;p=thirdparty%2Fkernel%2Fstable.git mm/damon/ops-common: call folio_test_lru() after folio_get() damon_get_folio() speculatively calls folio_test_lru() before folio_try_get(). The folio can get freed and reallocated to a tail page. In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered. Remove the speculative call. Also mark folio_test_lru() check right after folio_try_get() success as no more unlikely. The race should be rare. Also the problem can happen only if the kernel has enabled CONFIG_DEBUG_VM_PGFLAGS. No real world report of this issue has been made so far. This fix is based on only theoretical analysis. That said, a bug is a bug. A similar issue was also fixed via commit 3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a reference in next_uptodate_folio()"). I don't expect this change will make a meaningful impact to DAMON performance in the real world, though I will be happy to be corrected from the real world reports. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1] Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") Signed-off-by: SeongJae Park Cc: Fernand Sieber Cc: Leonard Foerster Cc: Shakeel Butt Cc: # 5.15.x Signed-off-by: Andrew Morton --- diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c index 8c6d613425c1..c3e4c871b0bb 100644 --- a/mm/damon/ops-common.c +++ b/mm/damon/ops-common.c @@ -32,9 +32,9 @@ struct folio *damon_get_folio(unsigned long pfn) return NULL; folio = page_folio(page); - if (!folio_test_lru(folio) || !folio_try_get(folio)) + if (!folio_try_get(folio)) return NULL; - if (unlikely(page_folio(page) != folio || !folio_test_lru(folio))) { + if (unlikely(page_folio(page) != folio) || !folio_test_lru(folio)) { folio_put(folio); folio = NULL; }