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[209.132.180.67]) by mx.google.com with ESMTP id y7si12295537pgc.236.2018.11.11.05.04.53; Sun, 11 Nov 2018 05:05:10 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=jkieru3A; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727953AbeKKWxD (ORCPT + 99 others); Sun, 11 Nov 2018 17:53:03 -0500 Received: from mail-qk1-f195.google.com ([209.85.222.195]:36697 "EHLO mail-qk1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727510AbeKKWxD (ORCPT ); Sun, 11 Nov 2018 17:53:03 -0500 Received: by mail-qk1-f195.google.com with SMTP id o125so9164641qkf.3 for ; Sun, 11 Nov 2018 05:04:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=rnBlG7472MsHKS6fCFX38wZUoRGSjjtO4xY3qxu6Dv8=; b=jkieru3AyPXdJOlI+fErpNFFcp80QCs04lQz2p71VagZrGqzMTZ5l9wJJLiFkef0+Z OL1cuoTiNWGSLvZ18zMvu+g9F7J5EYzLaqXt6y6AZlkFdQRw4x4nuRmAIIi28XSig4nq /RhdS09RpqUoyHiCvMRMqQ8zLOsu7SwL1xksq+cSTbpi6SdQxH+WC1AHqKCEeZWNvVUU 83377rg9S1ODT50J3Dro7b+Os8ZXAWpsJG2PSPhOJCxO86rtJfpo0yuSgczjfYt7KC/O IlevzmpzNz2TQM/2cSt+HqjtiHOC1kLuZh/Cw/M+QnyApLJTjL0o2Mbt1Xbu1P4uxRxN 9Vng== 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=rnBlG7472MsHKS6fCFX38wZUoRGSjjtO4xY3qxu6Dv8=; b=B5wep2y91ivLxODJuj97iBZUpJcB0gUd6nvrhPDpR4rsZi7RXPv/fkoStLAkTKXnKd 8NoYDpnI7MYhL4KD5i74z4ZfyWeI1SebKOlpoeRiVi7Xo+xgHARzpB3ZqkkNn0r7VcJx M+B/2diXDCz+g0BzZv9jdTyc5iHXpGlCut1JlPyHQLJCbxNB5jgBP38OqQja9C+NIca8 e0hvNlVMQrbP+nSwYfZoUX2vy+Vf6Ibs3Sv3Nakd859tXvd7BX+Y/f0JcwFaf0NaMX3u IMxUDUAjblxk1iZZMr15YbAzJDu97jIkAPATe8qsePwMR1iVgvlSrxCIJblGC8fItcNq /OAg== X-Gm-Message-State: AGRZ1gKj2jTqjihioJkl1UKXvf+DO6jRXqEUXkUFFEzulCnsvw7v51Ik e9qkPK7RMUEmTKfJ8b5le7YipVG1k58g37vi8Aw= X-Received: by 2002:a0c:d268:: with SMTP id o37mr15771283qvh.136.1541941470544; Sun, 11 Nov 2018 05:04:30 -0800 (PST) MIME-Version: 1.0 References: <20181110181101.24557-1-andriy.shevchenko@linux.intel.com> In-Reply-To: <20181110181101.24557-1-andriy.shevchenko@linux.intel.com> From: Andy Shevchenko Date: Sun, 11 Nov 2018 15:04:18 +0200 Message-ID: Subject: Re: [PATCH v1 1/5] drivercore: Revert "deferral race condition fix" To: Andy Shevchenko Cc: "Rafael J. Wysocki" , Greg Kroah-Hartman , Linux Kernel Mailing List , Hans de Goede , Grant Likely , Peter Ujfalusi , Andrzej Hajda 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 I seems Grant's mail delivery bounces messages. I delibirately reduced the Cc list for sake of ping Grant in case it would pass. On Sat, Nov 10, 2018 at 8:12 PM Andy Shevchenko wrote: > > Consider the following scenario. > > There are two independent devices coupled together by functional dependencies: > - USB OTG (dwc3-pci) > - extcon (tested with extcon-intel-mrfld, not yet in upstream) > > Each of the driver services a corresponding device is built as a module. In the > Buildroot environment the modules are probed by alphabetical ordering of their > modaliases. The latter comes to the case when USB OTG driver will be probed > first followed by extcon one. > > So, if the platform anticipates extcon device to be appeared, in the above case > we will get deferred probe of USB OTG, because of ordering. > > Now, a cherry on top of the cake, the deferred probing list contains > the only two modules, i.e. USB OTG and extcon. Due to above circumstances, > values in the local_trigger_count and deferred_trigger_count are not the same, > and thus provokes deferred probe triggering again and again. > > ... > [ 20.678332] platform dwc3.0.auto: Retrying from deferred list > [ 20.694743] platform dwc3.0.auto: Driver dwc3 requests probe deferral > [ 20.701254] platform dwc3.0.auto: Added to deferred list > [ 20.706620] platform dwc3.0.auto: driver_deferred_probe_add_trigger 1 2 > [ 20.713732] platform dwc3.0.auto: Retrying from deferred list > [ 20.730035] platform dwc3.0.auto: Driver dwc3 requests probe deferral > [ 20.736540] platform dwc3.0.auto: Added to deferred list > [ 20.741889] platform dwc3.0.auto: driver_deferred_probe_add_trigger 3 4 > [ 20.748991] platform dwc3.0.auto: Retrying from deferred list > [ 20.765416] platform dwc3.0.auto: Driver dwc3 requests probe deferral > [ 20.771914] platform dwc3.0.auto: Added to deferred list > [ 20.777279] platform dwc3.0.auto: driver_deferred_probe_add_trigger 5 6 > ... > > Deeper investigation shows the culprit commit 58b116bce136 > ("drivercore: deferral race condition fix") which was dedicated to fix some > other issue while bringing a regression. > > This reverts commit 58b116bce13612e5aa6fcd49ecbd4cf8bb59e835 for good until > we will have better solution. > > Cc: Grant Likely > Cc: Peter Ujfalusi > Cc: Greg Kroah-Hartman > Cc: Mark Brown > Cc: Felipe Balbi > Cc: Andrzej Hajda > Signed-off-by: Andy Shevchenko > --- > drivers/base/dd.c | 27 ++------------------------- > 1 file changed, 2 insertions(+), 25 deletions(-) > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > index 169412ee4ae8..9a966e45fda5 100644 > --- a/drivers/base/dd.c > +++ b/drivers/base/dd.c > @@ -53,7 +53,6 @@ > static DEFINE_MUTEX(deferred_probe_mutex); > static LIST_HEAD(deferred_probe_pending_list); > static LIST_HEAD(deferred_probe_active_list); > -static atomic_t deferred_trigger_count = ATOMIC_INIT(0); > static struct dentry *deferred_devices; > static bool initcalls_done; > > @@ -143,17 +142,6 @@ static bool driver_deferred_probe_enable = false; > * This functions moves all devices from the pending list to the active > * list and schedules the deferred probe workqueue to process them. It > * should be called anytime a driver is successfully bound to a device. > - * > - * Note, there is a race condition in multi-threaded probe. In the case where > - * more than one device is probing at the same time, it is possible for one > - * probe to complete successfully while another is about to defer. If the second > - * depends on the first, then it will get put on the pending list after the > - * trigger event has already occurred and will be stuck there. > - * > - * The atomic 'deferred_trigger_count' is used to determine if a successful > - * trigger has occurred in the midst of probing a driver. If the trigger count > - * changes in the midst of a probe, then deferred processing should be triggered > - * again. > */ > static void driver_deferred_probe_trigger(void) > { > @@ -166,7 +154,6 @@ static void driver_deferred_probe_trigger(void) > * into the active list so they can be retried by the workqueue > */ > mutex_lock(&deferred_probe_mutex); > - atomic_inc(&deferred_trigger_count); > list_splice_tail_init(&deferred_probe_pending_list, > &deferred_probe_active_list); > mutex_unlock(&deferred_probe_mutex); > @@ -434,19 +421,9 @@ EXPORT_SYMBOL_GPL(device_bind_driver); > static atomic_t probe_count = ATOMIC_INIT(0); > static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue); > > -static void driver_deferred_probe_add_trigger(struct device *dev, > - int local_trigger_count) > -{ > - driver_deferred_probe_add(dev); > - /* Did a trigger occur while probing? Need to re-trigger if yes */ > - if (local_trigger_count != atomic_read(&deferred_trigger_count)) > - driver_deferred_probe_trigger(); > -} > - > static int really_probe(struct device *dev, struct device_driver *drv) > { > int ret = -EPROBE_DEFER; > - int local_trigger_count = atomic_read(&deferred_trigger_count); > bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE) && > !drv->suppress_bind_attrs; > > @@ -463,7 +440,7 @@ static int really_probe(struct device *dev, struct device_driver *drv) > > ret = device_links_check_suppliers(dev); > if (ret == -EPROBE_DEFER) > - driver_deferred_probe_add_trigger(dev, local_trigger_count); > + driver_deferred_probe_add(dev); > if (ret) > return ret; > > @@ -559,7 +536,7 @@ static int really_probe(struct device *dev, struct device_driver *drv) > case -EPROBE_DEFER: > /* Driver requested deferred probing */ > dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name); > - driver_deferred_probe_add_trigger(dev, local_trigger_count); > + driver_deferred_probe_add(dev); > break; > case -ENODEV: > case -ENXIO: > -- > 2.19.1 > -- With Best Regards, Andy Shevchenko