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=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 11B9DC433DB for ; Sat, 27 Mar 2021 14:32:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9257619E5 for ; Sat, 27 Mar 2021 14:32:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230220AbhC0Obl (ORCPT ); Sat, 27 Mar 2021 10:31:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:46560 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229980AbhC0ObU (ORCPT ); Sat, 27 Mar 2021 10:31:20 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 23E7F61971; Sat, 27 Mar 2021 14:31:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1616855480; bh=K3B3wn5O49X7pYMRnz2Miw/eCiO8vGc9WeAkqSPq/e8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ODwi2je5W88UiTQEcBFH3/2TXBGigWnPnrRryFnbOeDzWtVCrw7dAkTCDiRoOPK+4 3WKdLTAA92zPQph2k+QrmD3W32XEEV85osrr2d/kyiYVdJpDlfF61xWV7EYuCUf5fw A9+E6Xylphx2YALJUmRzk0/nn9hhI3cvcTbm+h9Y= Date: Sat, 27 Mar 2021 15:31:18 +0100 From: Greg Kroah-Hartman To: Du Cheng Cc: Matthew Wilcox , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org, Shuah Khan , syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com Subject: Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign() Message-ID: References: <20210327140702.4916-1-ducheng2@gmail.com> <20210327142520.GA5271@ThinkCentre-M83> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210327142520.GA5271@ThinkCentre-M83> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sat, Mar 27, 2021 at 10:25:20PM +0800, Du Cheng wrote: > On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote: > > Adding the xarray maintainer... > > > > On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote: > > > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC) > > > due to internal use of per_cpu variables, which requires preemption > > > disabling/enabling. > > > > > > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller > > > > > > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com > > > Signed-off-by: Du Cheng > > > --- > > > changelog > > > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep > > > v2: revert to GFP_ATOMIC but add preemption disable/enable protection > > > > > > net/qrtr/qrtr.c | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c > > > index edb6ac17ceca..6361f169490e 100644 > > > --- a/net/qrtr/qrtr.c > > > +++ b/net/qrtr/qrtr.c > > > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port) > > > mutex_lock(&qrtr_port_lock); > > > if (!*port) { > > > min_port = QRTR_MIN_EPH_SOCKET; > > > + idr_preload(GFP_ATOMIC); > > > rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC); > > > + idr_preload_end(); > > > > This seems "odd" to me. We are asking idr_alloc_u32() to abide by > > GFP_ATOMIC, so why do we need to "preload" it with the same type of > > allocation? > > > > Is there something in the idr/radix/xarray code that can't really handle > > GFP_ATOMIC during a "normal" idr allocation that is causing this warning > > to be hit? Why is this change the "correct" one? > > > > thanks, > > > > greg k-h > > > >From the comment above idr_preload() in lib/radix-tree.c:1460 > /** > * idr_preload - preload for idr_alloc() > * @gfp_mask: allocation mask to use for preloading > * > * Preallocate memory to use for the next call to idr_alloc(). This function > * returns with preemption disabled. It will be enabled by idr_preload_end(). > */ > > idr_alloc is a very simple wrapper around idr_alloc_u32(). > > On top of radix_tree_node_alloc() which is called by idr_alloc_u32(), there is > this comment at line 244 in the same radix-tree.c > /* > * This assumes that the caller has performed appropriate preallocation, and > * that the caller has pinned this thread of control to the current CPU. > */ > > Therefore the preload/preload_end are necessary, or at least should have > preemption disabled Ah, so it's disabling preemption that is the key here. Still odd, why is GFP_ATOMIC not sufficient in a normal idr_alloc() call to keep things from doing stuff like this? Feels like a lot of "internal knowledge" is needed here to use this api properly... Matthew, is the above change really correct? thanks, greg k-h