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 AEBD3C433FE for ; Mon, 31 Jan 2022 23:31:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229564AbiAaXba (ORCPT ); Mon, 31 Jan 2022 18:31:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49282 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229457AbiAaXba (ORCPT ); Mon, 31 Jan 2022 18:31:30 -0500 Received: from mail-pg1-x52d.google.com (mail-pg1-x52d.google.com [IPv6:2607:f8b0:4864:20::52d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7B543C061714 for ; Mon, 31 Jan 2022 15:31:30 -0800 (PST) Received: by mail-pg1-x52d.google.com with SMTP id s16so13579738pgs.13 for ; Mon, 31 Jan 2022 15:31:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=H6tEMYobP7+G4jgA5hVF3vhoENh1fbXIUfhfOrDsbEg=; b=1aEb90z5eqGyOxcarrvJThvqXMyh8ALG56+4thL0dF+8CIPbqWAnk7IVMQlCU1M3Qp pjsoLfrZo+4J0VYeoWqbb9GEqp+VdZmvSFvQ5oDfE+ijMUGeg5uIeiJBcDZsv8rcIo9n N8eqUDUOIhZIle12u9t7K9eC2xRerq9LX/tA4bD4Iu3xp0woty3u4eil+xbo2zLj4nBa SuhiGNsan/KgHqKqiTJMP+enjOopH3wqG81fQv3eIzccQJl1/Yz637I0qFrrVmpC6qYc MN41vR5ymojqwhYMI0N7vvV99LcIMJRbACq2HhaMggktsTZpIqNFP+k2RcQsZhkB5Nst 013A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=H6tEMYobP7+G4jgA5hVF3vhoENh1fbXIUfhfOrDsbEg=; b=bKGAZXFLMta2UcbJbdPLrcdNKZ5q+HeXZGWqpYnr/He6PePXrvtWKq/Msnl4LVLgNf tti5wQBfWqXTzh5RHfZ1wkTQHCyvJkC1Gs32NE4kJ3j2+Ldi2hJRJLVNijFpnKRzd6XK EJ2UNU0ahUE+NJkn7XKktsImY94wkMQDHotJHuF9T7lZxA9Yk7mU86KbSItqltm7Qcoa +lwL0R1lHnJWZghE3iqGFRBX4uS7hyAzyOFHwMaIuCHbGjLiJ8IlP3IjQv5jVQBmMu4B PZ3eD/ZYbHN89T6CsYQybwq26/eXZDgCKF7jWrefVFnvQlf+WV/46snCnqZbwoE/j6Q3 hE3w== X-Gm-Message-State: AOAM532/By38FcFBPv8sD4YOGn/wkSwPmlLwZ+XqiyK7pZGgWIw0SSA5 JTTK2h2d+XtEsuZcRxKXj7/R6Vxxuv4B/6+m70ysmmx+/aw= X-Google-Smtp-Source: ABdhPJx0H6KJhvBY/aAzniN8BZM2cYXpwW59Ub1gGMlKc9Vx4sLVb4Q4obNYuwyLveRbjpENPuLJYBiDEj+cdEsL3ho= X-Received: by 2002:a63:85c6:: with SMTP id u189mr18348635pgd.437.1643671890007; Mon, 31 Jan 2022 15:31:30 -0800 (PST) MIME-Version: 1.0 References: <164298420439.3018233.5113217660229718675.stgit@dwillia2-desk3.amr.corp.intel.com> <164316562430.3437160.122223070771602475.stgit@dwillia2-desk3.amr.corp.intel.com> <20220131155934.000064ac@Huawei.com> In-Reply-To: <20220131155934.000064ac@Huawei.com> From: Dan Williams Date: Mon, 31 Jan 2022 15:31:22 -0800 Message-ID: Subject: Re: [PATCH v4 16/40] cxl/core/port: Use dedicated lock for decoder target list To: Jonathan Cameron Cc: linux-cxl@vger.kernel.org, Ben Widawsky , Linux PCI Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Mon, Jan 31, 2022 at 7:59 AM Jonathan Cameron wrote: > > On Tue, 25 Jan 2022 18:54:36 -0800 > Dan Williams wrote: > > > 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 > Suggested additional tidy up inline. > > Thanks, > > Jonathan > > > --- > > 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; > > Now you don't have a lock to unlock above, the only path that can > hit this if (rc < 0) is an if (rc < 0) in the for loop. > Perhaps just return directly there. Yeah, looks good.