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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 34F83C636CD for ; Fri, 10 Feb 2023 17:29:02 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 77DF36B0162; Fri, 10 Feb 2023 12:29:01 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 735F16B0163; Fri, 10 Feb 2023 12:29:01 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 61D5F6B0164; Fri, 10 Feb 2023 12:29:01 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 51A166B0162 for ; Fri, 10 Feb 2023 12:29:01 -0500 (EST) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 2DC2C1C6A51 for ; Fri, 10 Feb 2023 17:29:01 +0000 (UTC) X-FDA: 80452067682.16.EB3A6E0 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by imf09.hostedemail.com (Postfix) with ESMTP id 2F072140022 for ; Fri, 10 Feb 2023 17:28:56 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf09.hostedemail.com: domain of jonathan.cameron@huawei.com designates 185.176.79.56 as permitted sender) smtp.mailfrom=jonathan.cameron@huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1676050137; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rKimVvBv8Zgu3851fmKR8m8i/SQe+mvxPAuuguTnwVo=; b=Rtlzg92a+BNFTFfFHkfGxIEL26ElSMufjUDsQbleitq9JEzbf+Wrq/sSqLpDR3FY2rMpJn IwFzF+rjseCp42WMBaFhsBhfr6fiNYzZqZZ0jP8ZFmNUP5xEkyLiWWVRm3rBhPbFkXZz1e dKyXN9WzKgSJcFR9u3WYranuMAUCwOA= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf09.hostedemail.com: domain of jonathan.cameron@huawei.com designates 185.176.79.56 as permitted sender) smtp.mailfrom=jonathan.cameron@huawei.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1676050137; a=rsa-sha256; cv=none; b=fn8lkCz00j7Pfgm6jt2yF9m1x0MgRy7DwmyCvlT0N64qiiGMtafe17TQc5wf78McdRxAr6 du/oat87aPM3yaXGiLY+uVbjm1dFUbeboMWa7SuB37QEEQK+ZXtrHsQmqGkRawOmShgHtt +QSqGiOKTPchnRAe3fXd3lDWqH88Nro= Received: from lhrpeml500005.china.huawei.com (unknown [172.18.147.206]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4PD0w72WBwz67Qtq; Sat, 11 Feb 2023 01:24:23 +0800 (CST) Received: from localhost (10.81.210.211) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.17; Fri, 10 Feb 2023 17:28:51 +0000 Date: Fri, 10 Feb 2023 17:28:50 +0000 From: Jonathan Cameron To: Dan Williams CC: , , , , Subject: Re: [PATCH v2 01/20] cxl/memdev: Fix endpoint port removal Message-ID: <20230210172850.00001d5b@Huawei.com> In-Reply-To: <167601992789.1924368.8083994227892600608.stgit@dwillia2-xfh.jf.intel.com> References: <167601992097.1924368.18291887895351917895.stgit@dwillia2-xfh.jf.intel.com> <167601992789.1924368.8083994227892600608.stgit@dwillia2-xfh.jf.intel.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.81.210.211] X-ClientProxiedBy: lhrpeml500001.china.huawei.com (7.191.163.213) To lhrpeml500005.china.huawei.com (7.191.163.240) X-CFilter-Loop: Reflected X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2F072140022 X-Stat-Signature: eqkhmkoj84h8ef93bmjmr8uar9ofehex X-HE-Tag: 1676050136-470858 X-HE-Meta: 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 colOxo7e waPw1bhuZ7pIcVMrRRZ1L/0qL02RWTtXKjdNo3+I2xbbant3ZzL836zWGc8Oo9BQk+e/UZ2pFKTWuTXmQRUutRozs7I0GccfE5brJoujUFVZMYpSZMZn8NhWLTNMNC1XLakIHpKjUIQm1qZ49GasyEUuWrvN90XlK+5efTZhk4gLgkQcrVkjYbqcmbmD80woShYjnxC/ob1AY48jagxgUJif0qval9ZSmq6mB5ZNqEqkVyRW8iVnJXon2/r2PhIAc+45hmbdcW9xRtqe3XnaVeW0NQn2l/GhNpgn1sldDTEYleiwtUPphDDANRw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 10 Feb 2023 01:05:27 -0800 Dan Williams wrote: > Testing of ram region support [1], stimulates a long standing bug in > cxl_detach_ep() where some cxl_ep_remove() cleanup is skipped due to > inability to walk ports after dports have been unregistered. That > results in a failure to re-register a memdev after the port is > re-enabled leading to a crash like the following: > > cxl_port_setup_targets: cxl region4: cxl_host_bridge.0:port4 iw: 1 ig: 256 > general protection fault, ... > [..] > RIP: 0010:cxl_region_setup_targets+0x897/0x9e0 [cxl_core] > dev_name at include/linux/device.h:700 > (inlined by) cxl_port_setup_targets at drivers/cxl/core/region.c:1155 > (inlined by) cxl_region_setup_targets at drivers/cxl/core/region.c:1249 > [..] > Call Trace: > > attach_target+0x39a/0x760 [cxl_core] > ? __mutex_unlock_slowpath+0x3a/0x290 > cxl_add_to_region+0xb8/0x340 [cxl_core] > ? lockdep_hardirqs_on+0x7d/0x100 > discover_region+0x4b/0x80 [cxl_port] > ? __pfx_discover_region+0x10/0x10 [cxl_port] > device_for_each_child+0x58/0x90 > cxl_port_probe+0x10e/0x130 [cxl_port] > cxl_bus_probe+0x17/0x50 [cxl_core] > > Change the port ancestry walk to be by depth rather than by dport. This > ensures that even if a port has unregistered its dports a deferred > memdev cleanup will still be able to cleanup the memdev's interest in > that port. > > The parent_port->dev.driver check is only needed for determining if the > bottom up removal beat the top-down removal, but cxl_ep_remove() can > always proceed. Why can cxl_ep_remove() always proceed? What stops it racing? Is it that we are holding a reference to the port at the time of the call so the release callback can't be called until we drop that? Anyhow, good to have a little more detail on the 'why' in the patch description (particularly for those reading this when half asleep like me ;) > > Fixes: 2703c16c75ae ("cxl/core/port: Add switch port enumeration") > Link: http://lore.kernel.org/r/167564534874.847146.5222419648551436750.stgit@dwillia2-xfh.jf.intel.com [1] > Signed-off-by: Dan Williams > --- > drivers/cxl/core/memdev.c | 1 + > drivers/cxl/core/port.c | 58 +++++++++++++++++++++++++-------------------- > drivers/cxl/cxlmem.h | 2 ++ > 3 files changed, 35 insertions(+), 26 deletions(-) > > diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c > index a74a93310d26..3a8bc2b06047 100644 > --- a/drivers/cxl/core/memdev.c > +++ b/drivers/cxl/core/memdev.c > @@ -246,6 +246,7 @@ static struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds, > if (rc < 0) > goto err; > cxlmd->id = rc; > + cxlmd->depth = -1; > > dev = &cxlmd->dev; > device_initialize(dev); > diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c > index 410c036c09fa..317bcf4dbd9d 100644 > --- a/drivers/cxl/core/port.c > +++ b/drivers/cxl/core/port.c > @@ -1207,6 +1207,7 @@ int cxl_endpoint_autoremove(struct cxl_memdev *cxlmd, struct cxl_port *endpoint) > > get_device(&endpoint->dev); > dev_set_drvdata(dev, endpoint); > + cxlmd->depth = endpoint->depth; > return devm_add_action_or_reset(dev, delete_endpoint, cxlmd); > } > EXPORT_SYMBOL_NS_GPL(cxl_endpoint_autoremove, CXL); > @@ -1241,50 +1242,55 @@ static void reap_dports(struct cxl_port *port) > } > } > > +struct detach_ctx { > + struct cxl_memdev *cxlmd; > + int depth; > +}; > static void cxl_detach_ep(void *data) > { > struct cxl_memdev *cxlmd = data; > - struct device *iter; > > - for (iter = &cxlmd->dev; iter; iter = grandparent(iter)) { > - struct device *dport_dev = grandparent(iter); > + for (int i = cxlmd->depth - 1; i >= 1; i--) { > struct cxl_port *port, *parent_port; > + struct detach_ctx ctx = { > + .cxlmd = cxlmd, > + .depth = i, > + }; > + struct device *dev; > struct cxl_ep *ep; > bool died = false; > > - if (!dport_dev) > - break; > - > - port = find_cxl_port(dport_dev, NULL); > - if (!port) > - continue; > - > - if (is_cxl_root(port)) { > - put_device(&port->dev); > + dev = bus_find_device(&cxl_bus_type, NULL, &ctx, > + port_has_memdev); > + if (!dev) > continue; > - } > + port = to_cxl_port(dev); > > parent_port = to_cxl_port(port->dev.parent); > device_lock(&parent_port->dev); > - if (!parent_port->dev.driver) { > - /* > - * The bottom-up race to delete the port lost to a > - * top-down port disable, give up here, because the > - * parent_port ->remove() will have cleaned up all > - * descendants. > - */ > - device_unlock(&parent_port->dev); > - put_device(&port->dev); > - continue; > - } > - > device_lock(&port->dev); > ep = cxl_ep_load(port, cxlmd); > dev_dbg(&cxlmd->dev, "disconnect %s from %s\n", > ep ? dev_name(ep->ep) : "", dev_name(&port->dev)); > cxl_ep_remove(port, ep); > if (ep && !port->dead && xa_empty(&port->endpoints) && > - !is_cxl_root(parent_port)) { > + !is_cxl_root(parent_port) && parent_port->dev.driver) { > /* > * This was the last ep attached to a dynamically > * enumerated port. Block new cxl_add_ep() and garbage