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=-14.6 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_IN_DEF_DKIM_WL autolearn=ham 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 D54F9C433E0 for ; Thu, 25 Jun 2020 16:49:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A362C20775 for ; Thu, 25 Jun 2020 16:49:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="UXNdRwbZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391032AbgFYQtZ (ORCPT ); Thu, 25 Jun 2020 12:49:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40454 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390935AbgFYQtY (ORCPT ); Thu, 25 Jun 2020 12:49:24 -0400 Received: from mail-ot1-x344.google.com (mail-ot1-x344.google.com [IPv6:2607:f8b0:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 77B6DC08C5C1 for ; Thu, 25 Jun 2020 09:49:24 -0700 (PDT) Received: by mail-ot1-x344.google.com with SMTP id t6so5868292otk.9 for ; Thu, 25 Jun 2020 09:49:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=dpLir0KN1fSiFUAnU5SYwq+aUgno301uMg/TCjtgcTs=; b=UXNdRwbZrO+vE+usgaoKsP0CdDAddXk1tIGwLHSU7cQWnP66wJ5t+/8TVUtaFEmrdL kP3+HCYqgFoH0pZUK8uVe5Dupj+fm7WgK3mHRQucL0MVLif+yQbwSWWZ2NXuxLhUF8HE sHHqz5wtXZp5Yksu3OSyEyPIKOBQQ5FSA3CwJ3Eb3HjkppNX5e8YUJG3BZEm5tIYH3Ct aXoS7CekNFO6dy7x7GSbjbTZ5BqLnQ50RNdzYXPLf9DfGhGyTtEf5YvdfYuWi9amIenU yvX9GDgdQG01p5d+xcfSw8p1zFz7czjpeSaRVZ8y3JpgLQ71xeyy5Q6SM7D3ykCF3SE2 QoUA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=dpLir0KN1fSiFUAnU5SYwq+aUgno301uMg/TCjtgcTs=; b=EcfLbBIuD9NRBZ9ZfsiCQmNVs8+0tP4FlNTBSxajIAD8Sh2tGJU8gKh6jhdjyKr58N CecSA325AXY+XXL+DrKPtwM/XBttuxs3N6pZuGpBY5jkP5IWoiNAfhCUe1aZJgL/atca oG6EsGWIIDa1j1d84i36hW3lQnRxAroKrG0SavaJqRhywfCiDhgFGU1y3cweAMKBX47B xm1kJBquxk6RJMYPG6vazv58kbtqduB5RofgB9AVI7biDIQJEGBEtNLgfG6+x9GTqgp1 LTsRcgyWFwMt9eISKQ+g9Qx6Z6Rl9vOARzE+4zO3eAkctQ5xEEV2+mLFFx2SiWINNJhk t6GQ== X-Gm-Message-State: AOAM530XX9Avu43XYR39a87JOwSbl2aCvWunH7tJAc2rr6pNyLhvDEjM o3YHv2bD128pwC4D5zyvTDEiJXGbvbbnXqYtFnD6ag== X-Google-Smtp-Source: ABdhPJw75jtpWcrsgg4j8jrmGbPCwKktdzBqBh3bNDPjFrGgR+iMpgHLcNYj//oxt1QnvrS8FRMtCSTvI2wwXfGC13w= X-Received: by 2002:a9d:6048:: with SMTP id v8mr29627919otj.231.1593103763385; Thu, 25 Jun 2020 09:49:23 -0700 (PDT) MIME-Version: 1.0 References: <20200625032430.152447-1-saravanak@google.com> In-Reply-To: From: Saravana Kannan Date: Thu, 25 Jun 2020 09:48:47 -0700 Message-ID: Subject: Re: [PATCH v1] driver core: Fix suspend/resume order issue with deferred probe To: "Rafael J. Wysocki" Cc: Greg Kroah-Hartman , Geert Uytterhoeven , "Cc: Android Kernel" , "Rafael J. Wysocki" , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dropping Feng Kan and Toan Le because their mails are bouncing. On Thu, Jun 25, 2020 at 8:19 AM Rafael J. Wysocki wrote: > > On Thu, Jun 25, 2020 at 5:24 AM Saravana Kannan wrote: > > > > Under the following conditions: > > - driver A is built in and can probe device-A > > - driver B is a module and can probe device-B > > - device-A is supplier of device-B > > > > Without this patch: > > 1. device-A is added. > > 2. device-B is added. > > 3. dpm_list is now [device-A, device-B]. > > 4. driver-A defers probe of device-A. > > 5. deferred probe of device-A is reattempted > > 6. device-A is moved to end of dpm_list. > > 6. dpm_list is now [device-B, device-A]. > > 7. driver-B is loaded and probes device-B. > > 8. dpm_list stays as [device-B, device-A]. > > > > Suspend (which goes in the reverse order of dpm_list) fails because > > device-A (supplier) is suspended before device-B (consumer). > > > > With this patch: > > 1. device-A is added. > > 2. device-B is added. > > 3. dpm_list is now [device-A, device-B]. > > 4. driver-A defers probe of device-A. > > 5. deferred probe of device-A is reattempted later. > > 6. dpm_list is now [device-B, device-A]. > > 7. driver-B is loaded and probes device-B. > > 8. dpm_list is now [device-A, device-B]. > > > > Suspend works because device-B (consumer) is suspended before device-A > > (supplier). > > > > Fixes: 494fd7b7ad10 ("PM / core: fix deferred probe breaking suspend resume order") > > Fixes: 716a7a259690 ("driver core: fw_devlink: Add support for batching fwnode parsing") > > Cc: Geert Uytterhoeven > > Signed-off-by: Saravana Kannan > > --- > > drivers/base/dd.c | 16 ++++++++++++++++ > > 1 file changed, 16 insertions(+) > > > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > > index 9a1d940342ac..52b2148c7983 100644 > > --- a/drivers/base/dd.c > > +++ b/drivers/base/dd.c > > @@ -109,6 +109,8 @@ static void deferred_probe_work_func(struct work_struct *work) > > * probe makes that very unsafe. > > */ > > device_pm_move_to_tail(dev); > > + /* Greg/Rafael: SHOULD I DELETE THIS? ^^ I think I should, but > > + * I'm worried if it'll have some unintended consequeneces. */ > > Yes, this needs to go away if you make the other change. > > > > > dev_dbg(dev, "Retrying from deferred list\n"); > > bus_probe_device(dev); > > @@ -557,6 +559,20 @@ static int really_probe(struct device *dev, struct device_driver *drv) > > goto re_probe; > > } > > > > + /* > > + * The devices are added to the dpm_list (resume/suspend (reverse > > + * order) list) as they are registered with the driver core. But the > > + * order the devices are added doesn't necessarily match the real > > + * dependency order. > > + * > > + * The successful probe order is a much better signal. If a device just > > + * probed successfully, then we know for sure that all the devices that > > + * probed before it don't depend on the device. So, we can safely move > > + * the device to the end of the dpm_list. As more devices probe, > > + * they'll automatically get ordered correctly. > > + */ > > + device_pm_move_to_tail(dev); > > But it would be good to somehow limit this to the devices affected by > deferred probing or we'll end up reordering dpm_list unnecessarily for > many times in the actual majority of cases. Yes, lots of unnecessary reordering, but doing it only for deferred probes IS the problem. In the example I gave, the consumer is never deferred probe because the supplier happens to finish probing before the consumer probe is even attempted. I'm open to other suggestions, but I think this is needed for all the cases or at least more cases to be handled correctly. One alternative I was thinking was not adding the device to the dpm_list until it's probed. But I have the vague feeling of other things between device_add() and device probe that expect the device to be in the dpm_list. -Saravana