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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 5239DC33C9E for ; Thu, 30 Jan 2020 04:20:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 19F1E206D5 for ; Thu, 30 Jan 2020 04:20:21 +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="gIVBU7Bf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727296AbgA3EUU (ORCPT ); Wed, 29 Jan 2020 23:20:20 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:35276 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726871AbgA3EUU (ORCPT ); Wed, 29 Jan 2020 23:20:20 -0500 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=JcdAYnVQLCb8oRIYH7JBoQDKxVGZLa/gBb3aPfXmOGY=; b=gIVBU7BfX+LKPHHjnSQP2L7xh xjrpq80QPZ4DPbhgYrO5KqDdaZkkJfN/V7HPDRUATYJtgYJnGholvI9i9i7oMbmWf9tMLIe2reWvc qeWXf2Sloh+l9bNS1nKEkDOf3w6mkZMl9bsPE9kXBoSg8CE9+BPAIlwYVdDWASRfI6BHEJA6jV881 gDVqMr8gyaNT71X0lqPJVrXUkl9n9RThht/y2xxPTwQ2uO+L8apw4Ur5qatocUZjrmUNJ4M/xN4aQ L3LJxfrGUyVbOf8GFJhNAWQNa4ZgNWPUEzhJ0RbotBQH1hqrdYmvvTICgXRJjT67T+6wzIkpvhSzA os25Ch9Qw==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1ix1JL-0004TE-Fp; Thu, 30 Jan 2020 04:20:11 +0000 Date: Wed, 29 Jan 2020 20:20:11 -0800 From: Matthew Wilcox To: Qian Cai Cc: akpm@linux-foundation.org, dennis@kernel.org, tj@kernel.org, cl@linux.com, elver@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/util: fix a data race in __vm_enough_memory() Message-ID: <20200130042011.GI6615@bombadil.infradead.org> References: <20200130025133.5232-1-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200130025133.5232-1-cai@lca.pw> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 29, 2020 at 09:51:33PM -0500, Qian Cai wrote: > "vm_committed_as.count" could be accessed concurrently as reported by > KCSAN, > > read to 0xffffffff923164f8 of 8 bytes by task 1268 on cpu 38: > __vm_enough_memory+0x43/0x280 mm/util.c:801 > mmap_region+0x1b2/0xb90 mm/mmap.c:1726 > do_mmap+0x45c/0x700 > vm_mmap_pgoff+0xc0/0x130 > vm_mmap+0x71/0x90 > elf_map+0xa1/0x1b0 > load_elf_binary+0x9de/0x2180 > search_binary_handler+0xd8/0x2b0 > __do_execve_file+0xb61/0x1080 > __x64_sys_execve+0x5f/0x70 > do_syscall_64+0x91/0xb47 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > write to 0xffffffff923164f8 of 8 bytes by task 1265 on cpu 41: > percpu_counter_add_batch+0x83/0xd0 lib/percpu_counter.c:91 > exit_mmap+0x178/0x220 include/linux/mman.h:68 > mmput+0x10e/0x270 > flush_old_exec+0x572/0xfe0 > load_elf_binary+0x467/0x2180 > search_binary_handler+0xd8/0x2b0 > __do_execve_file+0xb61/0x1080 > __x64_sys_execve+0x5f/0x70 > do_syscall_64+0x91/0xb47 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Since only the read is operating as lockless, fix it by using > READ_ONLY() for it to avoid any possible false warning due to load You mean READ_ONCE ... > { > long allowed; > > - VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) < > + VM_WARN_ONCE(READ_ONCE(vm_committed_as.count) < > -(s64)vm_committed_as_batch * num_online_cpus(), I'm really not a fan of exposing the internals of a percpu_counter outside the percpu_counter.h file. Why shouldn't this be fixed by putting the READ_ONCE() inside percpu_counter_read()?