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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 5BDBDCA9EA0 for ; Fri, 25 Oct 2019 15:17:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2EAC521D7B for ; Fri, 25 Oct 2019 15:17:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="UpxPiSJ9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2440582AbfJYPRj (ORCPT ); Fri, 25 Oct 2019 11:17:39 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:51654 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2439061AbfJYPRj (ORCPT ); Fri, 25 Oct 2019 11:17:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=wnD87SJx6lKsZsUrTYB01i6mFsKAYC9XIXrBi0X2yaQ=; b=UpxPiSJ9dKwzMBowzOeApoA9a 3A//h++j8jOOZxPe8AAmMhWc3HvHpTPVot8a6Q3cdOayAkc9Rt52E/P2HNwUaohJ7rP+8EGEZgEUG W3s6bD3aS5tEKHOFD3FDXq8CuGjcot3jRq8o0unCNt0eme31janUb3+s8TbdebHbSlUuqOqvDNFJQ BCMNWAKuIayY/bqVVovy8hP23yTNVKic852aDK8XlHoauEc3EFJ+yUUuEwBD7BqjKI9VwiLpp3Yo8 7of3k8nb3ByyMbk4hg7Nyc4nrzQWR1J1iLj+eJycz9QRBmg/9AdW39eb/DNK5vFQs6QmLIt+17SGV DyYVudAIQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1iO1LO-00048W-8B; Fri, 25 Oct 2019 15:17:38 +0000 Date: Fri, 25 Oct 2019 08:17:38 -0700 From: Matthew Wilcox To: zhong jiang Cc: gregkh@linuxfoundation.org, stable@vger.kernel.org, vbabka@suse.cz, mhocko@suse.com, linux-mm@kvack.org Subject: Re: [RPF STABLE PATCH] mm/memfd: should be lock the radix_tree when iterating its slot Message-ID: <20191025151738.GP2963@bombadil.infradead.org> References: <1571929400-12147-1-git-send-email-zhongjiang@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1571929400-12147-1-git-send-email-zhongjiang@huawei.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Thu, Oct 24, 2019 at 11:03:20PM +0800, zhong jiang wrote: > + xa_lock_irq(&mapping->i_pages); ... > if (need_resched()) { > slot = radix_tree_iter_resume(slot, &iter); > - cond_resched_rcu(); > + cond_resched_lock(&mapping->i_pages.xa_lock); Ooh, this isn't right. We're taking the lock, disabling interrupts, then dropping the lock and rescheduling without reenabling interrupts. If this ever triggers then we'll get a scheduling-while-atomic error. Fortunately (?) need_resched() can almost never be set while we're holding a spinlock with interrupts disabled (thanks to peterz for telling me that when I asked for a cond_resched_lock_irq() a few years ago). So we need to take this patch further towards the current code. Here's a version for 4.14.y. Compile tested only. diff --git a/mm/shmem.c b/mm/shmem.c index 6c10f1d92251..deaea74ec1b3 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2657,11 +2657,12 @@ static void shmem_tag_pins(struct address_space *mapping) void **slot; pgoff_t start; struct page *page; + unsigned int tagged = 0; lru_add_drain(); start = 0; - rcu_read_lock(); + spin_lock_irq(&mapping->tree_lock); radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) { page = radix_tree_deref_slot(slot); if (!page || radix_tree_exception(page)) { @@ -2670,18 +2671,19 @@ static void shmem_tag_pins(struct address_space *mapping) continue; } } else if (page_count(page) - page_mapcount(page) > 1) { - spin_lock_irq(&mapping->tree_lock); radix_tree_tag_set(&mapping->page_tree, iter.index, SHMEM_TAG_PINNED); - spin_unlock_irq(&mapping->tree_lock); } - if (need_resched()) { - slot = radix_tree_iter_resume(slot, &iter); - cond_resched_rcu(); - } + if (++tagged % 1024) + continue; + + slot = radix_tree_iter_resume(slot, &iter); + spin_unlock_irq(&mapping->tree_lock); + cond_resched(); + spin_lock_irq(&mapping->tree_lock); } - rcu_read_unlock(); + spin_unlock_irq(&mapping->tree_lock); } /*