From patchwork Wed Jan 26 02:54:36 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dan Williams X-Patchwork-Id: 12724496 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 A4DCAC5DF62 for ; Wed, 26 Jan 2022 02:54:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236663AbiAZCyk (ORCPT ); Tue, 25 Jan 2022 21:54:40 -0500 Received: from mga04.intel.com ([192.55.52.120]:65436 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236514AbiAZCyi (ORCPT ); Tue, 25 Jan 2022 21:54:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1643165678; x=1674701678; h=subject:from:to:cc:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=wj9FuH5h8qEM3wIELD4IvCj7rEfospIx8qsXu9H/tI8=; b=E5cHoR4dmQnO8izHAZYTi4ZFnJwZgRY8UtPGDgXX6dtczl5pcvNJTAN7 pmSuTs55vG0sGbF37NbFzbKqJOuyh006IEe+JveoVB3vVhBWlirtDL/pA aPx/lkat5ay8XKpMmRcmmRNdMHwPEXZutFCw6nX4DHKq7GQp4HJuVMuxj 2oid6ZpNvqideVC9kenHybWCeBNizSpCBFFVE23VssVdq866NJ5ER/bf4 FSsGSgRnCV9hlmXzhCHSgOTgia/3yykL4nW0uTXKgYHBzu4WahjOYxrJP DD7gY8WqtFhukFfT2nIUYuDy4f3wSExuUZaFPVbM0BZF8de2DzqbbBqDH Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10238"; a="245302694" X-IronPort-AV: E=Sophos;i="5.88,316,1635231600"; d="scan'208";a="245302694" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jan 2022 18:54:37 -0800 X-IronPort-AV: E=Sophos;i="5.88,316,1635231600"; d="scan'208";a="617838093" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.25]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jan 2022 18:54:37 -0800 Subject: [PATCH v4 16/40] cxl/core/port: Use dedicated lock for decoder target list From: Dan Williams To: linux-cxl@vger.kernel.org Cc: Ben Widawsky , linux-pci@vger.kernel.org Date: Tue, 25 Jan 2022 18:54:36 -0800 Message-ID: <164316562430.3437160.122223070771602475.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <164298420439.3018233.5113217660229718675.stgit@dwillia2-desk3.amr.corp.intel.com> References: <164298420439.3018233.5113217660229718675.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.18-3-g996c MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org Lockdep reports: ====================================================== WARNING: possible circular locking dependency detected 5.16.0-rc1+ #142 Tainted: G OE ------------------------------------------------------ cxl/1220 is trying to acquire lock: ffff979b85475460 (kn->active#144){++++}-{0:0}, at: __kernfs_remove+0x1ab/0x1e0 but task is already holding lock: ffff979b87ab38e8 (&dev->lockdep_mutex#2/4){+.+.}-{3:3}, at: cxl_remove_ep+0x50c/0x5c0 [cxl_core] ...where cxl_remove_ep() is a helper that wants to delete ports while holding a lock on the host device for that port. That sets up a lockdep violation whereby target_list_show() can not rely holding the decoder's device lock while walking the target_list. Switch to a dedicated seqlock for this purpose. Reported-by: Ben Widawsky Signed-off-by: Dan Williams --- Changes in v4: - Fix missing unlock in error exit case (Ben) drivers/cxl/core/port.c | 30 ++++++++++++++++++++++++------ drivers/cxl/cxl.h | 2 ++ 2 files changed, 26 insertions(+), 6 deletions(-) diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c index f58b2d502ac8..5188d47180f1 100644 --- a/drivers/cxl/core/port.c +++ b/drivers/cxl/core/port.c @@ -104,14 +104,11 @@ static ssize_t target_type_show(struct device *dev, } static DEVICE_ATTR_RO(target_type); -static ssize_t target_list_show(struct device *dev, - struct device_attribute *attr, char *buf) +static ssize_t emit_target_list(struct cxl_decoder *cxld, char *buf) { - struct cxl_decoder *cxld = to_cxl_decoder(dev); ssize_t offset = 0; int i, rc = 0; - cxl_device_lock(dev); for (i = 0; i < cxld->interleave_ways; i++) { struct cxl_dport *dport = cxld->target[i]; struct cxl_dport *next = NULL; @@ -127,10 +124,28 @@ static ssize_t target_list_show(struct device *dev, break; offset += rc; } - cxl_device_unlock(dev); if (rc < 0) return rc; + return offset; +} + +static ssize_t target_list_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + struct cxl_decoder *cxld = to_cxl_decoder(dev); + ssize_t offset; + unsigned int seq; + int rc; + + do { + seq = read_seqbegin(&cxld->target_lock); + rc = emit_target_list(cxld, buf); + } while (read_seqretry(&cxld->target_lock, seq)); + + if (rc < 0) + return rc; + offset = rc; rc = sysfs_emit_at(buf, offset, "\n"); if (rc < 0) @@ -494,15 +509,17 @@ static int decoder_populate_targets(struct cxl_decoder *cxld, goto out_unlock; } + write_seqlock(&cxld->target_lock); for (i = 0; i < cxld->nr_targets; i++) { struct cxl_dport *dport = find_dport(port, target_map[i]); if (!dport) { rc = -ENXIO; - goto out_unlock; + break; } cxld->target[i] = dport; } + write_sequnlock(&cxld->target_lock); out_unlock: cxl_device_unlock(&port->dev); @@ -543,6 +560,7 @@ static struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port, cxld->id = rc; cxld->nr_targets = nr_targets; + seqlock_init(&cxld->target_lock); dev = &cxld->dev; device_initialize(dev); device_set_pm_not_required(dev); diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h index 569cbe7f23d6..47c256ad105f 100644 --- a/drivers/cxl/cxl.h +++ b/drivers/cxl/cxl.h @@ -185,6 +185,7 @@ enum cxl_decoder_type { * @interleave_granularity: data stride per dport * @target_type: accelerator vs expander (type2 vs type3) selector * @flags: memory type capabilities and locking + * @target_lock: coordinate coherent reads of the target list * @nr_targets: number of elements in @target * @target: active ordered target list in current decoder configuration */ @@ -199,6 +200,7 @@ struct cxl_decoder { int interleave_granularity; enum cxl_decoder_type target_type; unsigned long flags; + seqlock_t target_lock; int nr_targets; struct cxl_dport *target[]; };