From 406f475a3058c2aafc1cf3fd27f9e394cc1a9db2 Mon Sep 17 00:00:00 2001 From: Xu Yu Date: Mon, 24 May 2021 15:52:53 +0800 Subject: [PATCH 2716/2944] alinux: mm, thp: relax migration wait when failed to get tail page fix #32167089 We notice that hung task happens in a conner but practical scenario when CONFIG_PREEMPT_NONE is enabled, as follows. CPU 0 CPU 1 CPU 2..Inf split_huge_page_to_list unmap_page split_huge_pmd_address __migration_entry_wait(head) __migration_entry_wait(tail) remap_page remove_migration_ptes rmap_walk_anon cond_resched Where __migration_entry_wait(tail) is occurred in kernel space, e.g., copy_to_user, which will immediately fault again without rescheduling, and thus occupy the cpu fully. When there are too many processes performing __migration_entry_wait on tail page, remap_page will never be done after cond_resched. This relaxes __migration_entry_wait on tail page, thus gives remap_page a chance to complete. Signed-off-by: Xu Yu Reviewed-by: Gang Deng --- mm/migrate.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index fc345ae..27050d3 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -330,8 +330,11 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep, * So, we use get_page_unless_zero(), here. Even failed, page fault * will occur again. */ - if (!get_page_unless_zero(page)) - goto out; + if (!get_page_unless_zero(page)) { + pte_unmap_unlock(ptep, ptl); + cond_resched(); + return; + } pte_unmap_unlock(ptep, ptl); wait_on_page_locked(page); put_page(page); -- 1.8.3.1