From patchwork Thu Jun 3 22:26:58 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hugh Dickins X-Patchwork-Id: 12298317 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 ; Thu, 3 Jun 2021 22:27:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B0425613F1 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 299B76B0036; Thu, 3 Jun 2021 18:27:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 24BC26B006C; Thu, 3 Jun 2021 18:27:11 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 075AA6B0070; Thu, 3 Jun 2021 18:27:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0116.hostedemail.com [216.40.44.116]) by kanga.kvack.org (Postfix) with ESMTP id C704B6B0036 for ; Thu, 3 Jun 2021 18:27:10 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 5FB1B82499A8 for ; Thu, 3 Jun 2021 22:27:10 +0000 (UTC) X-FDA: 78213849420.23.2631190 Received: from mail-pj1-f53.google.com (mail-pj1-f53.google.com [209.85.216.53]) by imf30.hostedemail.com (Postfix) with ESMTP id E3BD9E007A53 for ; Thu, 3 Jun 2021 22:26:53 +0000 (UTC) Received: by mail-pj1-f53.google.com with SMTP id lx17-20020a17090b4b11b029015f3b32b8dbso6345582pjb.0 for ; Thu, 03 Jun 2021 15:27:04 -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=Mh3I22fIciz7IpLidGJnBhW8Yda4ScTUKYP/lNxer1ofTLutPRu+r8EyRcnAlVENAb ymHslpzPqSykpXRZ5O6COmcfgwlfTKkPkqaw++Mt/KW6y4if8nh9csHivy3XxD092RW5 nAsO2BZmjBZ99CoT5ADAtghio3xztBZV0pW4WaMde+YedysD+m15ZLWqYvccZc0zrHxp eiRCHh4hJ1R1RIdU15dCWn4YwKtrExKRu+Zx9sSzK+xNqXVsBqDmxz0fg/Tf41Zd5hxa aB+dMC90TWnp6qCZUJXHPZyllb5lurSJul6pN95lYlsPwb7AR2w1UJ0ygSfPQl13Jx7+ YkXA== X-Gm-Message-State: AOAM532ep7RjwBSxjzzZf1yuhfelwkgYrXI9pGbMTrF2FXBsS3xlYlbX BYDAaadScICcjeVot8dSEws+iw== 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 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)); From patchwork Thu Jun 3 22:32:10 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hugh Dickins X-Patchwork-Id: 12298329 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 84DA5C47082 for ; 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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id v9sm84364pfn.22.2021.06.03.15.32.11 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Thu, 03 Jun 2021 15:32:12 -0700 (PDT) Date: Thu, 3 Jun 2021 15:32:10 -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 , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 6.2/7] mm: rmap: make try_to_unmap() void function Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=JjGzfKQz; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf16.hostedemail.com: domain of hughd@google.com designates 209.85.215.177 as permitted sender) smtp.mailfrom=hughd@google.com X-Stat-Signature: uoxdhckhkh6yf1yxwn8bko1c6gd3q4ee X-Rspamd-Queue-Id: 898D3801973B X-Rspamd-Server: rspam02 X-HE-Tag: 1622759540-254149 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 Currently try_to_unmap() return bool value by checking page_mapcount(), however this may return false positive since page_mapcount() doesn't check all subpages of compound page. The total_mapcount() could be used instead, but its cost is higher since it traverses all subpages. Actually the most callers of try_to_unmap() don't care about the return value at all. So just need check if page is still mapped by page_mapped() when necessary. And page_mapped() does bail out early when it finds mapped subpage. Suggested-by: Hugh Dickins Signed-off-by: Yang Shi Acked-by: Minchan Kim Reviewed-by: Shakeel Butt Acked-by: Kirill A. Shutemov Signed-off-by: Hugh Dickins --- v5: Rediffed by Hugh to fit before 7/7 in mm/thp series; akpm fixed grammar. v4: Updated the comment of try_to_unmap() per Minchan. Minor fix and patch reorder per Hugh. Collected ack tag from Hugh. include/linux/rmap.h | 2 +- mm/memory-failure.c | 15 +++++++-------- mm/rmap.c | 15 ++++----------- mm/vmscan.c | 3 ++- 4 files changed, 14 insertions(+), 21 deletions(-) --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -195,7 +195,7 @@ static inline void page_dup_rmap(struct int page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg, unsigned long *vm_flags); -bool try_to_unmap(struct page *, enum ttu_flags flags); +void try_to_unmap(struct page *, enum ttu_flags flags); /* Avoid racy checks */ #define PVMW_SYNC (1 << 0) --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1063,7 +1063,7 @@ static bool hwpoison_user_mappings(struc enum ttu_flags ttu = TTU_IGNORE_MLOCK; struct address_space *mapping; LIST_HEAD(tokill); - bool unmap_success = true; + bool unmap_success; int kill = 1, forcekill; struct page *hpage = *hpagep; bool mlocked = PageMlocked(hpage); @@ -1126,7 +1126,7 @@ static bool hwpoison_user_mappings(struc collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED); if (!PageHuge(hpage)) { - unmap_success = try_to_unmap(hpage, ttu); + try_to_unmap(hpage, ttu); } else { if (!PageAnon(hpage)) { /* @@ -1138,17 +1138,16 @@ static bool hwpoison_user_mappings(struc */ mapping = hugetlb_page_mapping_lock_write(hpage); if (mapping) { - unmap_success = try_to_unmap(hpage, - ttu|TTU_RMAP_LOCKED); + try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED); i_mmap_unlock_write(mapping); - } else { + } else pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page\n", pfn); - unmap_success = false; - } } else { - unmap_success = try_to_unmap(hpage, ttu); + try_to_unmap(hpage, ttu); } } + + unmap_success = !page_mapped(hpage); if (!unmap_success) pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n", pfn, page_mapcount(hpage)); --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1405,7 +1405,7 @@ static bool try_to_unmap_one(struct page /* * When racing against e.g. zap_pte_range() on another cpu, * in between its ptep_get_and_clear_full() and page_remove_rmap(), - * try_to_unmap() may return false when it is about to become true, + * try_to_unmap() may return before page_mapped() has become false, * if page table locking is skipped: use TTU_SYNC to wait for that. */ if (flags & TTU_SYNC) @@ -1756,9 +1756,10 @@ static int page_not_mapped(struct page * * Tries to remove all the page table entries which are mapping this * page, used in the pageout path. Caller must hold the page lock. * - * If unmap is successful, return true. Otherwise, false. + * It is the caller's responsibility to check if the page is still + * mapped when needed (use TTU_SYNC to prevent accounting races). */ -bool try_to_unmap(struct page *page, enum ttu_flags flags) +void try_to_unmap(struct page *page, enum ttu_flags flags) { struct rmap_walk_control rwc = { .rmap_one = try_to_unmap_one, @@ -1783,14 +1784,6 @@ bool try_to_unmap(struct page *page, enu rmap_walk_locked(page, &rwc); else rmap_walk(page, &rwc); - - /* - * When racing against e.g. zap_pte_range() on another cpu, - * in between its ptep_get_and_clear_full() and page_remove_rmap(), - * try_to_unmap() may return false when it is about to become true, - * if page table locking is skipped: use TTU_SYNC to wait for that. - */ - return !page_mapcount(page); } /** --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1499,7 +1499,8 @@ static unsigned int shrink_page_list(str if (unlikely(PageTransHuge(page))) flags |= TTU_SPLIT_HUGE_PMD; - if (!try_to_unmap(page, flags)) { + try_to_unmap(page, flags); + if (page_mapped(page)) { stat->nr_unmap_fail += nr_pages; if (!was_swapbacked && PageSwapBacked(page)) stat->nr_lazyfree_fail += nr_pages;