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=-0.8 required=3.0 tests=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 E7205C2BA1E for ; Mon, 6 Apr 2020 12:44:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C829E2054F for ; Mon, 6 Apr 2020 12:44:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728052AbgDFMoV (ORCPT ); Mon, 6 Apr 2020 08:44:21 -0400 Received: from s3.sipsolutions.net ([144.76.43.62]:57804 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727993AbgDFMoV (ORCPT ); Mon, 6 Apr 2020 08:44:21 -0400 Received: by sipsolutions.net with esmtpsa (TLS1.3:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.93) (envelope-from ) id 1jLR6j-009kcZ-Dx; Mon, 06 Apr 2020 14:44:05 +0200 Message-ID: Subject: Re: [PATCH] mac80211: fix race in ieee80211_register_hw() From: Johannes Berg To: Sumit Garg , linux-wireless@vger.kernel.org Cc: davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, matthias.schoepfer@ithinx.io, Philipp.Berg@liebherr.com, Michael.Weitner@liebherr.com, daniel.thompson@linaro.org, loic.poulain@linaro.org, stable@vger.kernel.org Date: Mon, 06 Apr 2020 14:44:02 +0200 In-Reply-To: <1586175677-3061-1-git-send-email-sumit.garg@linaro.org> (sfid-20200406_142251_569735_E1B08414) References: <1586175677-3061-1-git-send-email-sumit.garg@linaro.org> (sfid-20200406_142251_569735_E1B08414) Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.34.4 (3.34.4-1.fc31) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Mon, 2020-04-06 at 17:51 +0530, Sumit Garg wrote: > A race condition leading to a kernel crash is observed during invocation > of ieee80211_register_hw() on a dragonboard410c device having wcn36xx > driver built as a loadable module along with a wifi manager in user-space > waiting for a wifi device (wlanX) to be active. > > Sequence diagram for a particular kernel crash scenario: > > user-space ieee80211_register_hw() RX IRQ > +++++++++++++++++++++++++++++++++++++++++++++ > | | | > |<---wlan0---wiphy_register() | > |----start wlan0---->| | > | |<---IRQ---(RX packet) > | Kernel crash | > | due to unallocated | > | workqueue. | > | | | > | alloc_ordered_workqueue() | > | | | > | Misc wiphy init. | > | | | > | ieee80211_if_add() | > | | | > > As evident from above sequence diagram, this race condition isn't specific > to a particular wifi driver but rather the initialization sequence in > ieee80211_register_hw() needs to be fixed. Indeed, oops. > So re-order the initialization > sequence and the updated sequence diagram would look like: > > user-space ieee80211_register_hw() RX IRQ > +++++++++++++++++++++++++++++++++++++++++++++ > | | | > | alloc_ordered_workqueue() | > | | | > | Misc wiphy init. | > | | | > |<---wlan0---wiphy_register() | > |----start wlan0---->| | > | |<---IRQ---(RX packet) > | | | > | ieee80211_if_add() | > | | | Makes sense. > @@ -1254,6 +1250,14 @@ int ieee80211_register_hw(struct ieee80211_hw *hw) > local->sband_allocated |= BIT(band); > } > > + rtnl_unlock(); > + > + result = wiphy_register(local->hw.wiphy); > + if (result < 0) > + goto fail_wiphy_register; > + > + rtnl_lock(); I'm a bit worried about this unlock/relock here though. I think we only need the RTNL for the call to ieee80211_init_rate_ctrl_alg() and then later ieee80211_if_add(), so perhaps we can move that a little closer? All the stuff between is really just setting up local stuff, so doesn't really need to worry? johannes