mm/vmscan: Maintain TLB coherency in LRU code

As a workaround (and possibly a fix) for CPU spins observed on BCM2837,
use ptep_clear_flush_young instead of ptep_test_and_clear_young inside
lru_gen_look_around in order to expose PTE changes to the MMU. Note that
on architectures that don't require an explicit flush,
ptep_clear_flush_young just calls ptep_test_and_clear_young.

Signed-off-by: Phil Elwell <[email protected]>

mm/vmscan.c

@@ -4113,7 +4113,7 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 		if (!folio)
 			continue;
 
-		if (!ptep_clear_young_notify(vma, addr, pte + i))
+		if (!ptep_clear_flush_young_notify(vma, addr, pte + i))
 			continue;
 
 		young++;