From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 80843C49EB7 for ; Mon, 28 Jun 2021 14:37:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 69DBB61D5C for ; Mon, 28 Jun 2021 14:37:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235129AbhF1OjV (ORCPT ); Mon, 28 Jun 2021 10:39:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:36914 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233693AbhF1Oat (ORCPT ); Mon, 28 Jun 2021 10:30:49 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4647961CB7; Mon, 28 Jun 2021 14:27:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1624890433; bh=xTB3YB9ZX3NmGs64ppPafeBJ+1rD9FrGam3WAqOW1fc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=H8Gjyzm0/8duvQ42RNWcP+Epd0ioG4xqfbSdB8UzxsbP5BNRP5qnJaAX+PDevgJjz 6KaqzNlgX47JC5utK5/o+it90WilR/LpaCMxr+Gy0U6Iudvkgglt/LIpCwEMeyu2cv QuCyidFInyISGOzwTBEJFu5B0SRxzo/R+pfazV+E4nb6ne+5jXKprzqBWSw/ghbNpp F8FM11S201dEB+Spvkmw2FqudnMirv6wc0XoKcfZn0p/ikk5RWz7uub2Mn0Re+HRwF SYKmS4HGyzf9Mgo2Dj8vhE3dpI8/QFNuoSjaMj5Ao7OZSgZk7jsIi4oyVAWrTrHWRj 1O2j96muccyng== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Xu Yu , Hugh Dickins , Gang Deng , "Kirill A . Shutemov" , Matthew Wilcox , Andrew Morton , Linus Torvalds , Greg Kroah-Hartman Subject: [PATCH 5.10 074/101] mm, thp: use head page in __migration_entry_wait() Date: Mon, 28 Jun 2021 10:25:40 -0400 Message-Id: <20210628142607.32218-75-sashal@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210628142607.32218-1-sashal@kernel.org> References: <20210628142607.32218-1-sashal@kernel.org> MIME-Version: 1.0 X-KernelTest-Patch: http://kernel.org/pub/linux/kernel/v5.x/stable-review/patch-5.10.47-rc1.gz X-KernelTest-Tree: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git X-KernelTest-Branch: linux-5.10.y X-KernelTest-Patches: git://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git X-KernelTest-Version: 5.10.47-rc1 X-KernelTest-Deadline: 2021-06-30T14:25+00:00 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xu Yu commit ffc90cbb2970ab88b66ea51dd580469eede57b67 upstream. We notice that hung task happens in a corner but practical scenario when CONFIG_PREEMPT_NONE is enabled, as follows. Process 0 Process 1 Process 2..Inf split_huge_page_to_list unmap_page split_huge_pmd_address __migration_entry_wait(head) __migration_entry_wait(tail) remap_page (roll back) remove_migration_ptes rmap_walk_anon cond_resched Where __migration_entry_wait(tail) is occurred in kernel space, e.g., copy_to_user in fstat, 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 makes __migration_entry_wait operate on the compound head page, thus waits for remap_page to complete, whether the THP is split successfully or roll back. Note that put_and_wait_on_page_locked helps to drop the page reference acquired with get_page_unless_zero, as soon as the page is on the wait queue, before actually waiting. So splitting the THP is only prevented for a brief interval. Link: https://lkml.kernel.org/r/b9836c1dd522e903891760af9f0c86a2cce987eb.1623144009.git.xuyu@linux.alibaba.com Fixes: ba98828088ad ("thp: add option to setup migration entries during PMD split") Suggested-by: Hugh Dickins Signed-off-by: Gang Deng Signed-off-by: Xu Yu Acked-by: Kirill A. Shutemov Acked-by: Hugh Dickins Cc: Matthew Wilcox Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/migrate.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/migrate.c b/mm/migrate.c index 7982256a5125..278e6f3fa62c 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -326,6 +326,7 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep, goto out; page = migration_entry_to_page(entry); + page = compound_head(page); /* * Once page cache replacement of page migration started, page_count -- 2.30.2