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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 85022C4332F for ; Thu, 2 Sep 2021 21:58:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 720D660E8B for ; Thu, 2 Sep 2021 21:58:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347950AbhIBV7p (ORCPT ); Thu, 2 Sep 2021 17:59:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:55446 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347669AbhIBV7n (ORCPT ); Thu, 2 Sep 2021 17:59:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 488536056B; Thu, 2 Sep 2021 21:58:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1630619924; bh=ANDwkS9rBb2mlLAIfKtDDm9aLbrAyaB/cN4c+uXCLF0=; h=Date:From:To:Subject:In-Reply-To:From; b=mC9C6TGFRkvXfXVl7rZjnw2ME8MvoBgQwWERsYXx8CP9sjhclgbxvKJJKe07Sofv3 GntQxOBM671GDts5Rlz/00lAs5nwnI+u+152mLwFFmkT7oVwBSwHOc0RvvWUt8Xcqq 3nzAG0pUENX9AoLwBDS9TDS8IMR0akZwYCCwzCvY= Date: Thu, 02 Sep 2021 14:58:43 -0700 From: Andrew Morton To: akpm@linux-foundation.org, almasrymina@google.com, david@redhat.com, linux-mm@kvack.org, mhocko@suse.com, mike.kravetz@oracle.com, mm-commits@vger.kernel.org, naoya.horiguchi@linux.dev, osalvador@suse.de, songmuchun@bytedance.com, torvalds@linux-foundation.org, willy@infradead.org Subject: [patch 166/212] hugetlb: simplify prep_compound_gigantic_page ref count racing code Message-ID: <20210902215843.gOQ0PNv6O%akpm@linux-foundation.org> In-Reply-To: <20210902144820.78957dff93d7bea620d55a89@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Mike Kravetz Subject: hugetlb: simplify prep_compound_gigantic_page ref count racing code Code in prep_compound_gigantic_page waits for a rcu grace period if it notices a temporarily inflated ref count on a tail page. This was due to the identified potential race with speculative page cache references which could only last for a rcu grace period. This is overly complicated as this situation is VERY unlikely to ever happen. Instead, just quickly return an error. Also, only print a warning in prep_compound_gigantic_page instead of multiple callers. Link: https://lkml.kernel.org/r/20210809184832.18342-2-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz Cc: David Hildenbrand Cc: Matthew Wilcox Cc: Michal Hocko Cc: Mina Almasry Cc: Muchun Song Cc: Naoya Horiguchi Cc: Oscar Salvador Signed-off-by: Andrew Morton --- mm/hugetlb.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) --- a/mm/hugetlb.c~hugetlb-simplify-prep_compound_gigantic_page-ref-count-racing-code +++ a/mm/hugetlb.c @@ -1657,16 +1657,14 @@ static bool prep_compound_gigantic_page( * cache adding could take a ref on a 'to be' tail page. * We need to respect any increased ref count, and only set * the ref count to zero if count is currently 1. If count - * is not 1, we call synchronize_rcu in the hope that a rcu - * grace period will cause ref count to drop and then retry. - * If count is still inflated on retry we return an error and - * must discard the pages. + * is not 1, we return an error. An error return indicates + * the set of pages can not be converted to a gigantic page. + * The caller who allocated the pages should then discard the + * pages using the appropriate free interface. */ if (!page_ref_freeze(p, 1)) { - pr_info("HugeTLB unexpected inflated ref count on freshly allocated page\n"); - synchronize_rcu(); - if (!page_ref_freeze(p, 1)) - goto out_error; + pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n"); + goto out_error; } set_page_count(p, 0); set_compound_head(p, page); @@ -1830,7 +1828,6 @@ retry: retry = true; goto retry; } - pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n"); return NULL; } } @@ -2828,8 +2825,8 @@ static void __init gather_bootmem_preall prep_new_huge_page(h, page, page_to_nid(page)); put_page(page); /* add to the hugepage allocator */ } else { + /* VERY unlikely inflated ref count on a tail page */ free_gigantic_page(page, huge_page_order(h)); - pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n"); } /* _