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=-24.8 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=ham 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 29C17C47096 for ; Thu, 3 Jun 2021 22:27:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EEA70613F1 for ; Thu, 3 Jun 2021 22:27:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230412AbhFCW2x (ORCPT ); Thu, 3 Jun 2021 18:28:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36006 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229620AbhFCW2w (ORCPT ); Thu, 3 Jun 2021 18:28:52 -0400 Received: from mail-pl1-x629.google.com (mail-pl1-x629.google.com [IPv6:2607:f8b0:4864:20::629]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5A8C7C06174A for ; Thu, 3 Jun 2021 15:27:02 -0700 (PDT) Received: by mail-pl1-x629.google.com with SMTP id x10so3647031plg.3 for ; Thu, 03 Jun 2021 15:27:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=s5yPesF7sEWozm6wfz/tvzm6wYfI1FnnfGsX6uavdk0=; b=dddkEQ10ucFDB7ZZfF1p0ObMg4oGDxNtuqWzTKCZIIACiVojmFMGA6oEOmnvRIoBoz JtSfACXMYK1p9dtfs7o1U7JoeD5VVwf3PDNlOr+p2qYinR11eXQAVlHIB8/SYdle3JzC SUBIJdu67+swFWKvSoBNkCDgtpTW+XS8+GbAGEEI1oo7BXk2X/lRMZK61oD48/UWxNgn khY1TNPFItlMeizHaRIr/OsVf2COCOKaZQiVTV8aFHEKkAr1IByCboNbSL21tXMgUGrI uFZBo52ok4mwBMZsqcyPddZg2yoLn8alfwL+6aot1VnXVpKDdkVCjYug1e05USGmrxji 1sBw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version; bh=s5yPesF7sEWozm6wfz/tvzm6wYfI1FnnfGsX6uavdk0=; b=Z9bs3JJDUvvtZ98cxuTudCO7aUtLZvmmeKrXmxS0ThA2k1+w/6+FBeWKujr1kmuvdG n+Y+gQyCR3GS9NTPDjh1KOHwiJ2WPxx3GIomfTJpUzC25Gd3gTbAz9BDWuY37M1GwW+S CI5uJL+eRciFV38kESCHR7u641fXZsjcP6c7kUX4Gs93+U/j1yIZLDsc6mtkiVrHajdE CNn56SrgwcCDzwmA0DqUiuL8IleXV8Bxe33k872lOVs4JJjxFoxa6lzeLD7Nqu3rIuHZ tADpZ3ZY6Oj1YcK5dHhqkOe+blr5GcGsFzEMhks841IQirV/GRY8DAmRhA40tzz3SEd/ GVOA== X-Gm-Message-State: AOAM531DFd3Vd6EmKqAMkV+eZhIXt+vy93K/UJtu4hiCMySad7dbn5Jr tQBjdKrZA5xhy9UF8Gv9VRrNRA== X-Google-Smtp-Source: ABdhPJzQYnppn92XbOXwHSN2nMLzPzyYW4Gc6+3gA+f7iIVTLQReK3q6DaTA91XMC2xklVJ4kL6KVw== X-Received: by 2002:a17:90a:d24a:: with SMTP id o10mr13626649pjw.19.1622759221524; Thu, 03 Jun 2021 15:27:01 -0700 (PDT) Received: from eggly.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id q191sm75708pfq.108.2021.06.03.15.26.59 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Thu, 03 Jun 2021 15:27:00 -0700 (PDT) Date: Thu, 3 Jun 2021 15:26:58 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Hugh Dickins , "Kirill A. Shutemov" , Yang Shi , Wang Yugui , Matthew Wilcox , Naoya Horiguchi , Alistair Popple , Ralph Campbell , Zi Yan , Miaohe Lin , Minchan Kim , Jue Wang , Peter Xu , Jan Kara , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 6.1/7] mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split In-Reply-To: Message-ID: References: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yang Shi When debugging the bug reported by Wang Yugui [1], try_to_unmap() may fail, but the first VM_BUG_ON_PAGE() just checks page_mapcount() however it may miss the failure when head page is unmapped but other subpage is mapped. Then the second DEBUG_VM BUG() that check total mapcount would catch it. This may incur some confusion. And this is not a fatal issue, so consolidate the two DEBUG_VM checks into one VM_WARN_ON_ONCE_PAGE(). [1] https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@e16-tech.com/ Signed-off-by: Yang Shi Reviewed-by: Zi Yan Acked-by: Kirill A. Shutemov Signed-off-by: Hugh Dickins Cc: --- v5: Rediffed by Hugh to fit after 6/7 in his mm/thp series; Cc stable. v4: Updated the subject and commit log per Hugh. Reordered the patches per Hugh. v3: Incorporated the comments from Hugh. Keep Zi Yan's reviewed-by tag since there is no fundamental change against v2. v2: Removed dead code and updated the comment of try_to_unmap() per Zi Yan. mm/huge_memory.c | 26 ++++++++------------------ 1 file changed, 8 insertions(+), 18 deletions(-) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2350,19 +2350,19 @@ static void unmap_page(struct page *page { enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD; - bool unmap_success; VM_BUG_ON_PAGE(!PageHead(page), page); if (PageAnon(page)) ttu_flags |= TTU_SPLIT_FREEZE; - /* Make sure that the BUGs will not bite */ + /* If warning below, prevent a race in the mapped accounting */ if (IS_ENABLED(CONFIG_DEBUG_VM)) ttu_flags |= TTU_SYNC; - unmap_success = try_to_unmap(page, ttu_flags); - VM_BUG_ON_PAGE(!unmap_success, page); + try_to_unmap(page, ttu_flags); + + VM_WARN_ON_ONCE_PAGE(page_mapped(page), page); } static void remap_page(struct page *page, unsigned int nr) @@ -2673,7 +2673,7 @@ int split_huge_page_to_list(struct page struct deferred_split *ds_queue = get_deferred_split_queue(head); struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; - int count, mapcount, extra_pins, ret; + int extra_pins, ret; pgoff_t end; VM_BUG_ON_PAGE(is_huge_zero_page(head), head); @@ -2732,7 +2732,6 @@ int split_huge_page_to_list(struct page } unmap_page(head); - VM_BUG_ON_PAGE(compound_mapcount(head), head); /* block interrupt reentry in xa_lock and spinlock */ local_irq_disable(); @@ -2750,9 +2749,7 @@ int split_huge_page_to_list(struct page /* Prevent deferred_split_scan() touching ->_refcount */ spin_lock(&ds_queue->split_queue_lock); - count = page_count(head); - mapcount = total_mapcount(head); - if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) { + if (page_ref_freeze(head, 1 + extra_pins)) { if (!list_empty(page_deferred_list(head))) { ds_queue->split_queue_len--; list_del(page_deferred_list(head)); @@ -2772,16 +2769,9 @@ int split_huge_page_to_list(struct page __split_huge_page(page, list, end); ret = 0; } else { - if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) { - pr_alert("total_mapcount: %u, page_count(): %u\n", - mapcount, count); - if (PageTail(page)) - dump_page(head, NULL); - dump_page(page, "total_mapcount(head) > 0"); - BUG(); - } spin_unlock(&ds_queue->split_queue_lock); -fail: if (mapping) +fail: + if (mapping) xa_unlock(&mapping->i_pages); local_irq_enable(); remap_page(head, thp_nr_pages(head)); 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=-24.8 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 140DFC47096 for ; Thu, 3 Jun 2021 22:27:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B0425613F1 for ; 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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id q191sm75708pfq.108.2021.06.03.15.26.59 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Thu, 03 Jun 2021 15:27:00 -0700 (PDT) Date: Thu, 3 Jun 2021 15:26:58 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Hugh Dickins , "Kirill A. Shutemov" , Yang Shi , Wang Yugui , Matthew Wilcox , Naoya Horiguchi , Alistair Popple , Ralph Campbell , Zi Yan , Miaohe Lin , Minchan Kim , Jue Wang , Peter Xu , Jan Kara , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 6.1/7] mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split In-Reply-To: Message-ID: References: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Authentication-Results: imf30.hostedemail.com; dkim=temperror ("DNS error when getting key") header.d=google.com header.s=20161025 header.b=dddkEQ10; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf30.hostedemail.com: domain of hughd@google.com designates 209.85.216.53 as permitted sender) smtp.mailfrom=hughd@google.com X-Stat-Signature: 3k919dhiw3tc959i51ygd4ob5f9ha8h1 X-Rspamd-Queue-Id: E3BD9E007A53 X-Rspamd-Server: rspam02 X-HE-Tag: 1622759213-517821 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Yang Shi When debugging the bug reported by Wang Yugui [1], try_to_unmap() may fail, but the first VM_BUG_ON_PAGE() just checks page_mapcount() however it may miss the failure when head page is unmapped but other subpage is mapped. Then the second DEBUG_VM BUG() that check total mapcount would catch it. This may incur some confusion. And this is not a fatal issue, so consolidate the two DEBUG_VM checks into one VM_WARN_ON_ONCE_PAGE(). [1] https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@e16-tech.com/ Signed-off-by: Yang Shi Reviewed-by: Zi Yan Acked-by: Kirill A. Shutemov Signed-off-by: Hugh Dickins Cc: --- v5: Rediffed by Hugh to fit after 6/7 in his mm/thp series; Cc stable. v4: Updated the subject and commit log per Hugh. Reordered the patches per Hugh. v3: Incorporated the comments from Hugh. Keep Zi Yan's reviewed-by tag since there is no fundamental change against v2. v2: Removed dead code and updated the comment of try_to_unmap() per Zi Yan. mm/huge_memory.c | 26 ++++++++------------------ 1 file changed, 8 insertions(+), 18 deletions(-) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2350,19 +2350,19 @@ static void unmap_page(struct page *page { enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD; - bool unmap_success; VM_BUG_ON_PAGE(!PageHead(page), page); if (PageAnon(page)) ttu_flags |= TTU_SPLIT_FREEZE; - /* Make sure that the BUGs will not bite */ + /* If warning below, prevent a race in the mapped accounting */ if (IS_ENABLED(CONFIG_DEBUG_VM)) ttu_flags |= TTU_SYNC; - unmap_success = try_to_unmap(page, ttu_flags); - VM_BUG_ON_PAGE(!unmap_success, page); + try_to_unmap(page, ttu_flags); + + VM_WARN_ON_ONCE_PAGE(page_mapped(page), page); } static void remap_page(struct page *page, unsigned int nr) @@ -2673,7 +2673,7 @@ int split_huge_page_to_list(struct page struct deferred_split *ds_queue = get_deferred_split_queue(head); struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; - int count, mapcount, extra_pins, ret; + int extra_pins, ret; pgoff_t end; VM_BUG_ON_PAGE(is_huge_zero_page(head), head); @@ -2732,7 +2732,6 @@ int split_huge_page_to_list(struct page } unmap_page(head); - VM_BUG_ON_PAGE(compound_mapcount(head), head); /* block interrupt reentry in xa_lock and spinlock */ local_irq_disable(); @@ -2750,9 +2749,7 @@ int split_huge_page_to_list(struct page /* Prevent deferred_split_scan() touching ->_refcount */ spin_lock(&ds_queue->split_queue_lock); - count = page_count(head); - mapcount = total_mapcount(head); - if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) { + if (page_ref_freeze(head, 1 + extra_pins)) { if (!list_empty(page_deferred_list(head))) { ds_queue->split_queue_len--; list_del(page_deferred_list(head)); @@ -2772,16 +2769,9 @@ int split_huge_page_to_list(struct page __split_huge_page(page, list, end); ret = 0; } else { - if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) { - pr_alert("total_mapcount: %u, page_count(): %u\n", - mapcount, count); - if (PageTail(page)) - dump_page(head, NULL); - dump_page(page, "total_mapcount(head) > 0"); - BUG(); - } spin_unlock(&ds_queue->split_queue_lock); -fail: if (mapping) +fail: + if (mapping) xa_unlock(&mapping->i_pages); local_irq_enable(); remap_page(head, thp_nr_pages(head));