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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31120C433FE for ; Tue, 1 Mar 2022 13:31:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235039AbiCANbo (ORCPT ); Tue, 1 Mar 2022 08:31:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231678AbiCANbn (ORCPT ); Tue, 1 Mar 2022 08:31:43 -0500 Received: from alexa-out.qualcomm.com (alexa-out.qualcomm.com [129.46.98.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DD9F9D069; Tue, 1 Mar 2022 05:31:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1646141460; x=1677677460; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=6jTsJL2Nf6S109wFxCPWYCTVBMfXkFlLj36OQOqRjcc=; b=m8y+Gu8x1LkoaEH0vsJdVHviKkdSnmUY9d+WmxHCPoNBGv0qZvdGpHzo +5QYzqBhNxlurmNYp7FY763HrOEguMGoPjRgofOf4HHzfcgRlH4h1IgFu Wr4+yHHWZOmznSgwJRRM837Fbgy/G9J6Ql7xtVcZY3H9cAODMNbmz/vUV w=; Received: from ironmsg09-lv.qualcomm.com ([10.47.202.153]) by alexa-out.qualcomm.com with ESMTP; 01 Mar 2022 05:31:00 -0800 X-QCInternal: smtphost Received: from nasanex01c.na.qualcomm.com ([10.47.97.222]) by ironmsg09-lv.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Mar 2022 05:30:59 -0800 Received: from nalasex01a.na.qualcomm.com (10.47.209.196) by nasanex01c.na.qualcomm.com (10.47.97.222) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.15; Tue, 1 Mar 2022 05:30:59 -0800 Received: from [10.239.133.9] (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.15; Tue, 1 Mar 2022 05:30:55 -0800 Message-ID: Date: Tue, 1 Mar 2022 21:30:52 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.5.1 Subject: Re: [PATCH] coresight: Defer probe when the child dev is not probed Content-Language: en-US To: Mike Leach CC: Suzuki K Poulose , Mathieu Poirier , Leo Yan , "Alexander Shishkin" , Mao Jinlong , , , , , Tingwei Zhang , Yuanfang Zhang , Tao Zhang , Hao Zhang References: <20220228133112.3987-1-quic_jinlmao@quicinc.com> <861dd6e1-30dc-626e-3449-72d3b6822e7b@arm.com> From: Jinlong Mao In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01b.na.qualcomm.com (10.46.141.250) To nalasex01a.na.qualcomm.com (10.47.209.196) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Mike, On 3/1/2022 9:15 PM, Mike Leach wrote: > Hi, > > On Tue, 1 Mar 2022 at 11:42, Jinlong Mao wrote: >> On 2/28/2022 10:51 PM, Suzuki K Poulose wrote: >> >> Hi Jinlong >> >> On 28/02/2022 13:31, Mao Jinlong wrote: >> >> From: Mao Jinlong >> >> It is possible that when device probe, its child device is not >> probed. Then it will fail when add sysfs connection for the device. >> Make device defer probe when the child device is not probed. >> >> >> Please could you a bit a more specific on the exact issue ? >> I don't see a problem with probe deferral right now, with >> coresight/next. >> >> For e.g., >> >> root@juno-server:~# lsmod >> Module Size Used by >> coresight 73728 0 >> root@juno-server:~# ls /sys/bus/coresight/devices/ >> root@juno-server:~# modprobe coresight-etm4x >> root@juno-server:~# lsmod >> Module Size Used by >> coresight_etm4x 81920 0 >> coresight 73728 1 coresight_etm4x >> root@juno-server:~# ls /sys/bus/coresight/devices/ >> etm0 etm1 >> >> -- Note etm2-etm5 doesn't appear -- >> >> root@juno-server:~# modprobe coresight-funnel >> root@juno-server:~# lsmod >> Module Size Used by >> coresight_funnel 20480 0 >> coresight_etm4x 81920 0 >> coresight 73728 2 coresight_etm4x,coresight_funnel >> root@juno-server:~# ls /sys/bus/coresight/devices/ >> etm0 etm1 >> >> -- Still don't appear --- >> >> root@juno-server:~# modprobe coresight-replicator >> root@juno-server:~# ls /sys/bus/coresight/devices/ >> etm0 etm1 >> root@juno-server:~# modprobe coresight-tmc >> >> -- At this stage, the devices automatically get probed and appear -- >> root@juno-server:~# ls /sys/bus/coresight/devices/ >> etm0 etm1 etm2 etm3 etm4 etm5 funnel0 funnel1 funnel2 tmc_etf0 tmc_etr0 >> >> >> root@juno-server:~# lsmod >> Module Size Used by >> coresight_tmc 40960 0 >> coresight_replicator 20480 0 >> coresight_funnel 20480 0 >> coresight_etm4x 81920 0 >> coresight 73728 4 coresight_tmc,coresight_etm4x,coresight_replicator,coresight_funnel >> >> So, my question is, what is this patch trying to solve ? >> >> >> Cheers >> Suzuki >> >> Hi Suzuki, >> >> This issue happens when race condition happens. >> The condition is that the device and its child_device's probe happens at the same time. >> >> For example: device0 and its child device device1. >> Both of them are calling coresight_register function. device0 is calling coresight_fixup_device_conns. >> device1 is waiting for device0 to release the coresight_mutex. Because device1's csdev node is allocated, >> coresight_make_links will be called for device0. Then in coresight_add_sysfs_link, has_conns_grp is true >> for device0, but has_conns_grp is false for device1 as has_conns_grp is set to true in coresight_create_conns_sysfs_group . >> The probe of device0 will fail for at this condition. >> >> >> struct coresight_device *coresight_register(struct coresight_desc *desc) >> { >> ......... >> mutex_lock(&coresight_mutex); >> >> ret = coresight_create_conns_sysfs_group(csdev); >> if (!ret) >> ret = coresight_fixup_device_conns(csdev); >> if (!ret) >> ret = coresight_fixup_orphan_conns(csdev); >> if (!ret && cti_assoc_ops && cti_assoc_ops->add) >> cti_assoc_ops->add(csdev); >> >> mutex_unlock(&coresight_mutex); >> >> ......... >> >> } >> >> static int coresight_fixup_device_conns(struct coresight_device *csdev) >> { >> .......... >> conn->child_dev = >> coresight_find_csdev_by_fwnode(conn->child_fwnode); > The issue appears to be a constraint hidden in the lower layers of the code. > Would a better solution not be to alter the code here: > > if (conn->child_dev && conn->child_dev->has_conns_grp) { > ... > } else { > csdev->orphan = true; > } > > which would mean that the connection attempt would drop through to > label the connection as an orphan, to be cleaned up by the child > itself when it runs coresight_fixup_orphan_conns() > > Regards > > Mike Thanks Mike. Your recommended fix looks much better than my fix. Let me try with it and get back to you. Thanks Jinlong  Mao > >> if (conn->child_dev) { >> ret = coresight_make_links(csdev, conn, >> >> conn->child_dev); >> >> .......... >> >> } >> >> >> int coresight_add_sysfs_link(struct coresight_sysfs_link *info) >> { >> ................ >> if (!info->orig->has_conns_grp || !info->target->has_conns_grp) >> return -EINVAL; >> >> >> >> The probe fail issue is reproduced with reboot stress test on our internal device. >> >> With the patch, the probe fail issue is not reproduced. >> >> Thanks >> >> Jinlong Mao >> >> >> >> Signed-off-by: Mao Jinlong >> --- >> drivers/hwtracing/coresight/coresight-sysfs.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c >> index 34d2a2d31d00..7df9eb59bf2c 100644 >> --- a/drivers/hwtracing/coresight/coresight-sysfs.c >> +++ b/drivers/hwtracing/coresight/coresight-sysfs.c >> @@ -73,8 +73,10 @@ int coresight_add_sysfs_link(struct coresight_sysfs_link *info) >> if (!info->orig || !info->target || >> !info->orig_name || !info->target_name) >> return -EINVAL; >> - if (!info->orig->has_conns_grp || !info->target->has_conns_grp) >> + if (!info->orig->has_conns_grp) >> return -EINVAL; >> + if (!info->target->has_conns_grp) >> + return -EPROBE_DEFER; >> /* first link orig->target */ >> ret = sysfs_add_link_to_group(&info->orig->dev.kobj, >> >> >