From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f198.google.com (mail-pf1-f198.google.com [209.85.210.198]) by kanga.kvack.org (Postfix) with ESMTP id 9BA216B4461 for ; Mon, 26 Nov 2018 18:25:05 -0500 (EST) Received: by mail-pf1-f198.google.com with SMTP id 74so12513874pfk.12 for ; Mon, 26 Nov 2018 15:25:05 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id h191sor2685046pge.48.2018.11.26.15.25.04 for (Google Transport Security); Mon, 26 Nov 2018 15:25:04 -0800 (PST) Date: Mon, 26 Nov 2018 15:25:01 -0800 (PST) From: Hugh Dickins Subject: [PATCH 05/10] mm/khugepaged: fix crashes due to misaccounted holes In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: "Kirill A. Shutemov" , "Kirill A. Shutemov" , Matthew Wilcox , linux-mm@kvack.org Huge tmpfs testing on a shortish file mapped into a pmd-rounded extent hit shmem_evict_inode()'s WARN_ON(inode->i_blocks) followed by clear_inode()'s BUG_ON(inode->i_data.nrpages) when the file was later closed and unlinked. khugepaged's collapse_shmem() was forgetting to update mapping->nrpages on the rollback path, after it had added but then needs to undo some holes. There is indeed an irritating asymmetry between shmem_charge(), whose callers want it to increment nrpages after successfully accounting blocks, and shmem_uncharge(), when __delete_from_page_cache() already decremented nrpages itself: oh well, just add a comment on that to them both. And shmem_recalc_inode() is supposed to be called when the accounting is expected to be in balance (so it can deduce from imbalance that reclaim discarded some pages): so change shmem_charge() to update nrpages earlier (though it's rare for the difference to matter at all). Fixes: 800d8c63b2e98 ("shmem: add huge pages support") Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages") Signed-off-by: Hugh Dickins Cc: Kirill A. Shutemov Cc: stable@vger.kernel.org # 4.8+ --- mm/khugepaged.c | 5 ++++- mm/shmem.c | 6 +++++- 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 2070c316f06e..65e82f665c7c 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1506,9 +1506,12 @@ static void collapse_shmem(struct mm_struct *mm, khugepaged_pages_collapsed++; } else { struct page *page; + /* Something went wrong: roll back page cache changes */ - shmem_uncharge(mapping->host, nr_none); xas_lock_irq(&xas); + mapping->nrpages -= nr_none; + shmem_uncharge(mapping->host, nr_none); + xas_set(&xas, start); xas_for_each(&xas, page, end - 1) { page = list_first_entry_or_null(&pagelist, diff --git a/mm/shmem.c b/mm/shmem.c index ea26d7a0342d..e6558e49b42a 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -297,12 +297,14 @@ bool shmem_charge(struct inode *inode, long pages) if (!shmem_inode_acct_block(inode, pages)) return false; + /* nrpages adjustment first, then shmem_recalc_inode() when balanced */ + inode->i_mapping->nrpages += pages; + spin_lock_irqsave(&info->lock, flags); info->alloced += pages; inode->i_blocks += pages * BLOCKS_PER_PAGE; shmem_recalc_inode(inode); spin_unlock_irqrestore(&info->lock, flags); - inode->i_mapping->nrpages += pages; return true; } @@ -312,6 +314,8 @@ void shmem_uncharge(struct inode *inode, long pages) struct shmem_inode_info *info = SHMEM_I(inode); unsigned long flags; + /* nrpages adjustment done by __delete_from_page_cache() or caller */ + spin_lock_irqsave(&info->lock, flags); info->alloced -= pages; inode->i_blocks -= pages * BLOCKS_PER_PAGE; -- 2.20.0.rc0.387.gc7a69e6b6c-goog