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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 6FFE4C432BE for ; Wed, 1 Sep 2021 09:36:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4C77961027 for ; Wed, 1 Sep 2021 09:36:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243698AbhIAJhA (ORCPT ); Wed, 1 Sep 2021 05:37:00 -0400 Received: from foss.arm.com ([217.140.110.172]:35006 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243672AbhIAJg7 (ORCPT ); Wed, 1 Sep 2021 05:36:59 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5E4AB1042; Wed, 1 Sep 2021 02:36:02 -0700 (PDT) Received: from e120937-lin (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 67E0B3F766; Wed, 1 Sep 2021 02:36:01 -0700 (PDT) Date: Wed, 1 Sep 2021 10:35:58 +0100 From: Cristian Marussi To: rishabhb@codeaurora.org Cc: sudeep.holla@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, avajid@codeaurora.org, adharmap@codeaurora.org Subject: Re: [PATCH v3] firmware: arm_scmi: Free mailbox channels if probe fails Message-ID: <20210901093558.GL13160@e120937-lin> References: <1628111999-21595-1-git-send-email-rishabhb@codeaurora.org> <20210805105427.GU6592@e120937-lin> <51782599a01a6a22409d01e5fc1f8a50@codeaurora.org> <20210831054835.GJ13160@e120937-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210831054835.GJ13160@e120937-lin> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 31, 2021 at 06:48:35AM +0100, Cristian Marussi wrote: > On Mon, Aug 30, 2021 at 02:09:37PM -0700, rishabhb@codeaurora.org wrote: > > Hi Christian > > Hi Rishabh, > > thanks for looking into this kind of bad interactions. > > > There seems to be another issue here. The response from agent can be delayed > > causing a timeout during base protocol acquire, > > which leads to the probe failure. What I have observed is sometimes the > > failure of probe and rx_callback (due to a delayed message) > > happens at the same time on different cpus. > > Because of this race, the device memory may be cleared while the > > interrupt(rx_callback) is executing on another cpu. > > You are right that concurrency was not handled properly in this kind of > context and moreover, if you think about it, even the case of out of > order reception of responses and delayed_responses (type2 SCMI messages) > for asynchronous SCMI commands was not handled properly. > > > How do you propose we solve this? Do you think it is better to take the > > setting up of base and other protocols out of probe and > > in some delayed work? That would imply the device memory is not released > > until remove is called. Or should we add locking to > > the interrupt handler(scmi_rx_callback) and the cleanup in probe to avoid > > the race? > > > > These issues were more easily exposed by SCMI Virtio transport, so in > the series where I introduced scmi-virtio: > > https://lore.kernel.org/linux-arm-kernel/162848483974.232214.9506203742448269364.b4-ty@arm.com/ > > (which is now queued for v5.15 ... now on -next I think...finger crossed) > > I took the chance to rectify a couple of other things in the SCMI core > in the initial commits. > As an example, in the above series > > [PATCH v7 05/15] firmware: arm_scmi: Handle concurrent and out-of-order messages > > cares to add a refcount to xfers and some locking on xfers between TX > and RX path to avoid that a timed out xfer can vanish while the rx path > is concurrently working on it (as you said); moreover I handle the > condition (rare if not unplausible anyway) in which a transport delivers > out of order responses and delayed responses. > > I tested this scenarios on some fake emulated SCMI Virtio transport > where I could play any sort of mess and tricks to stress this limit > conditions, but you're more than welcome to verify if the race you are > seeing on Base protocol time out is solved (as I would hope :D) by this > series of mine. > > Let me know, any feedback is welcome. > > Btw, in the series above there are also other minor changes, but there > is also another more radical change needed to ensure correctness and > protection against stale old messages which maybe could interest you > in general if you are looking into SCMI: > > [PATCH v7 04/15] firmware: arm_scmi: Introduce monotonically increasing tokens > > Let me know if yo have other concerns. > Hi Rishabhb, just a quick remark, thinking again about your fail @probe scenario above I realized that while the concurrency patch I mentioned above could help on races against vanishing xfers when late timed-out responses are delivered, here we really are then also shutting down everything on failure, so there could be further issues between a very late invokation of scmi_rx_callback and the core devm_ helpers freeing the underlying xfer/cinfo/etc.. structs used by scmi-rx-callback itself (maybe this was already what you meant and I didn't get it,...sorry) On the other side, I don't feel that delaying Base init to a deferred worker is a viable solution since we need Base protocol init to be initialized and we need to just give up if we cannot communicate with the SCMI platform fw in such early stages. (Base protocol is really the only mandatory proto is I remember correctly the spec) Currenly I'm off and only glancing at mails but I'll have a thought about these issues once back in a few weeks time. Thanks, Cristian 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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 1F4A9C432BE for ; Wed, 1 Sep 2021 11:05:03 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D64B460F4B for ; Wed, 1 Sep 2021 11:05:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org D64B460F4B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=4SrUhTli+9bWmy0qM1p7RbTFg1dzolRELM7utverl2c=; b=EM28If2uu5eSv2 v0MwM+Z6pOIWR7tZjDrtMwBXxGbF+q+K5BPnmkv+WljRRpRiAdJJ8HozfLL0ikvkd0EA1JkHQMzhc 7LVTniKntpj3+rlS216+vx7RKdolEQmWDdmBaSBCzPSCTQ65d0iDyKnDrLE8HtOYfQKW16sTKVnQX T7DSIKnnvYqBY1B8Lo4XHBTCPLT4m/rxvDekCeahYuagX3Pw8ZuPgFvioSmp7F+2NNv6IGqxN5EZT z5OQfwKdq3FIU0tcBWPY8BOm+KOjg+W4mHAXIjXJIMAnvhRxesb++wMVekEfHNDJWu2ThXVPm8MKW 1D8vJ5IavsS57txi7jYA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mLO0v-005Pqr-3k; Wed, 01 Sep 2021 11:02:41 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mLMf8-004vYj-50 for linux-arm-kernel@lists.infradead.org; Wed, 01 Sep 2021 09:36:08 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5E4AB1042; Wed, 1 Sep 2021 02:36:02 -0700 (PDT) Received: from e120937-lin (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 67E0B3F766; Wed, 1 Sep 2021 02:36:01 -0700 (PDT) Date: Wed, 1 Sep 2021 10:35:58 +0100 From: Cristian Marussi To: rishabhb@codeaurora.org Cc: sudeep.holla@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, avajid@codeaurora.org, adharmap@codeaurora.org Subject: Re: [PATCH v3] firmware: arm_scmi: Free mailbox channels if probe fails Message-ID: <20210901093558.GL13160@e120937-lin> References: <1628111999-21595-1-git-send-email-rishabhb@codeaurora.org> <20210805105427.GU6592@e120937-lin> <51782599a01a6a22409d01e5fc1f8a50@codeaurora.org> <20210831054835.GJ13160@e120937-lin> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210831054835.GJ13160@e120937-lin> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210901_023606_370727_4D972F25 X-CRM114-Status: GOOD ( 38.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Aug 31, 2021 at 06:48:35AM +0100, Cristian Marussi wrote: > On Mon, Aug 30, 2021 at 02:09:37PM -0700, rishabhb@codeaurora.org wrote: > > Hi Christian > > Hi Rishabh, > > thanks for looking into this kind of bad interactions. > > > There seems to be another issue here. The response from agent can be delayed > > causing a timeout during base protocol acquire, > > which leads to the probe failure. What I have observed is sometimes the > > failure of probe and rx_callback (due to a delayed message) > > happens at the same time on different cpus. > > Because of this race, the device memory may be cleared while the > > interrupt(rx_callback) is executing on another cpu. > > You are right that concurrency was not handled properly in this kind of > context and moreover, if you think about it, even the case of out of > order reception of responses and delayed_responses (type2 SCMI messages) > for asynchronous SCMI commands was not handled properly. > > > How do you propose we solve this? Do you think it is better to take the > > setting up of base and other protocols out of probe and > > in some delayed work? That would imply the device memory is not released > > until remove is called. Or should we add locking to > > the interrupt handler(scmi_rx_callback) and the cleanup in probe to avoid > > the race? > > > > These issues were more easily exposed by SCMI Virtio transport, so in > the series where I introduced scmi-virtio: > > https://lore.kernel.org/linux-arm-kernel/162848483974.232214.9506203742448269364.b4-ty@arm.com/ > > (which is now queued for v5.15 ... now on -next I think...finger crossed) > > I took the chance to rectify a couple of other things in the SCMI core > in the initial commits. > As an example, in the above series > > [PATCH v7 05/15] firmware: arm_scmi: Handle concurrent and out-of-order messages > > cares to add a refcount to xfers and some locking on xfers between TX > and RX path to avoid that a timed out xfer can vanish while the rx path > is concurrently working on it (as you said); moreover I handle the > condition (rare if not unplausible anyway) in which a transport delivers > out of order responses and delayed responses. > > I tested this scenarios on some fake emulated SCMI Virtio transport > where I could play any sort of mess and tricks to stress this limit > conditions, but you're more than welcome to verify if the race you are > seeing on Base protocol time out is solved (as I would hope :D) by this > series of mine. > > Let me know, any feedback is welcome. > > Btw, in the series above there are also other minor changes, but there > is also another more radical change needed to ensure correctness and > protection against stale old messages which maybe could interest you > in general if you are looking into SCMI: > > [PATCH v7 04/15] firmware: arm_scmi: Introduce monotonically increasing tokens > > Let me know if yo have other concerns. > Hi Rishabhb, just a quick remark, thinking again about your fail @probe scenario above I realized that while the concurrency patch I mentioned above could help on races against vanishing xfers when late timed-out responses are delivered, here we really are then also shutting down everything on failure, so there could be further issues between a very late invokation of scmi_rx_callback and the core devm_ helpers freeing the underlying xfer/cinfo/etc.. structs used by scmi-rx-callback itself (maybe this was already what you meant and I didn't get it,...sorry) On the other side, I don't feel that delaying Base init to a deferred worker is a viable solution since we need Base protocol init to be initialized and we need to just give up if we cannot communicate with the SCMI platform fw in such early stages. (Base protocol is really the only mandatory proto is I remember correctly the spec) Currenly I'm off and only glancing at mails but I'll have a thought about these issues once back in a few weeks time. Thanks, Cristian _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel