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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id f13sm3722869qtv.83.2021.06.08.21.22.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Jun 2021 21:22:41 -0700 (PDT) Date: Tue, 8 Jun 2021 21:22:39 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.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 , Oscar Salvador , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 07/10] mm: thp: replace DEBUG_VM BUG with VM_WARN when unmap fails for split In-Reply-To: Message-ID: References: MIME-Version: 1.0 Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=NlAloZez; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf27.hostedemail.com: domain of hughd@google.com designates 209.85.219.48 as permitted sender) smtp.mailfrom=hughd@google.com X-Stat-Signature: yrz985xnzg8wn5bd3soq3bm8uoa9uxbh X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9E8E6801934C X-HE-Tag: 1623212558-68773 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: --- Patch inserted since the v1 series was posted. 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 | 24 +++++++----------------- 1 file changed, 7 insertions(+), 17 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 84ab735139dc..6d2a0119fc58 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2352,15 +2352,15 @@ static void unmap_page(struct page *page) { enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_SYNC | 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; - 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) @@ -2671,7 +2671,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) 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); @@ -2730,7 +2730,6 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) } unmap_page(head); - VM_BUG_ON_PAGE(compound_mapcount(head), head); /* block interrupt reentry in xa_lock and spinlock */ local_irq_disable(); @@ -2748,9 +2747,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) /* 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)); @@ -2770,16 +2767,9 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) __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));