From patchwork Fri Jun 26 03:29:24 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 223005 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=-4.0 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=no 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 6B07EC433DF for ; Fri, 26 Jun 2020 03:29:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 449322081A for ; Fri, 26 Jun 2020 03:29:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593142167; bh=BOOtNScon/F8RSvOC5TUchukW1Vi8hVtCQbXchQ1dOQ=; h=Date:From:To:Subject:In-Reply-To:List-ID:From; b=KVCjF3qvMONXlrXKBNHJhcrkaXfoXO8SAxgvVHcVJzlWytAK251NfrFc0TZ1BWQNX GDjAGEWXJVXlAGgobVm/Rpd7FxALdAZGZTKgsAS5x2MLSVHyFUjl8Fy7rnPCe4fDeV DX8yjIybK/IJB2ujpdb1Yc5KPoIpTXajq1qufyyI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728331AbgFZD3Z (ORCPT ); Thu, 25 Jun 2020 23:29:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:47838 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728259AbgFZD3Z (ORCPT ); Thu, 25 Jun 2020 23:29:25 -0400 Received: from localhost.localdomain (c-71-198-47-131.hsd1.ca.comcast.net [71.198.47.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E41342084D; Fri, 26 Jun 2020 03:29:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593142165; bh=BOOtNScon/F8RSvOC5TUchukW1Vi8hVtCQbXchQ1dOQ=; h=Date:From:To:Subject:In-Reply-To:From; b=sRprRrBw/9EDVnMNdWctQPhoi3O8zHvwTGASoW5AT5SJhIWFPBirb3Wgu6g48S58v 0EqwezipKb4zBuKLVJyruPUyxkt0O6f4NxZD8U91ZD4+CkICaR/Iu4bYUaXHUMqzNc Gcr7S2riV8pzpWxhT6IwA57626zHpuNEOVAcYNAA= Date: Thu, 25 Jun 2020 20:29:24 -0700 From: Andrew Morton To: akpm@linux-foundation.org, alex.shi@linux.alibaba.com, hughd@google.com, liwang@redhat.com, mgorman@techsingularity.net, mm-commits@vger.kernel.org, stable@vger.kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz Subject: [patch 03/32] mm, compaction: make capture control handling safe wrt interrupts Message-ID: <20200626032924.PiPdcjulX%akpm@linux-foundation.org> In-Reply-To: <20200625202807.b630829d6fa55388148bee7d@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Vlastimil Babka Subject: mm, compaction: make capture control handling safe wrt interrupts Hugh reports: : While stressing compaction, one run oopsed on NULL capc->cc in : __free_one_page()'s task_capc(zone): compact_zone_order() had been : interrupted, and a page was being freed in the return from interrupt. : : Though you would not expect it from the source, both gccs I was using (a : 4.8.1 and a 7.5.0) had chosen to compile compact_zone_order() with the : ".cc = &cc" implemented by mov %rbx,-0xb0(%rbp) immediately before callq : compact_zone - long after the "current->capture_control = &capc". An : interrupt in between those finds capc->cc NULL (zeroed by an earlier rep : stos). : : This could presumably be fixed by a barrier() before setting : current->capture_control in compact_zone_order(); but would also need more : care on return from compact_zone(), in order not to risk leaking a page : captured by interrupt just before capture_control is reset. : : Maybe that is the preferable fix, but I felt safer for task_capc() to : exclude the rather surprising possibility of capture at interrupt time. I have checked that gcc10 also behaves the same. The advantage of fix in compact_zone_order() is that we don't add another test in the page freeing hot path, and that it might prevent future problems if we stop exposing pointers to uninitialized structures in current task. So this patch implements the suggestion for compact_zone_order() with barrier() (and WRITE_ONCE() to prevent store tearing) for setting current->capture_control, and prevents page leaking with WRITE_ONCE/READ_ONCE in the proper order. Link: http://lkml.kernel.org/r/20200616082649.27173-1-vbabka@suse.cz Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction") Signed-off-by: Vlastimil Babka Reported-by: Hugh Dickins Suggested-by: Hugh Dickins Acked-by: Hugh Dickins Cc: Alex Shi Cc: Li Wang Cc: Mel Gorman Cc: [5.1+] Signed-off-by: Andrew Morton --- mm/compaction.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) --- a/mm/compaction.c~mm-compaction-make-capture-control-handling-safe-wrt-interrupts +++ a/mm/compaction.c @@ -2316,15 +2316,26 @@ static enum compact_result compact_zone_ .page = NULL, }; - current->capture_control = &capc; + /* + * Make sure the structs are really initialized before we expose the + * capture control, in case we are interrupted and the interrupt handler + * frees a page. + */ + barrier(); + WRITE_ONCE(current->capture_control, &capc); ret = compact_zone(&cc, &capc); VM_BUG_ON(!list_empty(&cc.freepages)); VM_BUG_ON(!list_empty(&cc.migratepages)); - *capture = capc.page; - current->capture_control = NULL; + /* + * Make sure we hide capture control first before we read the captured + * page pointer, otherwise an interrupt could free and capture a page + * and we would leak it. + */ + WRITE_ONCE(current->capture_control, NULL); + *capture = READ_ONCE(capc.page); return ret; }