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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 529CEC433F5 for ; Thu, 30 Sep 2021 10:12:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 34690615E2 for ; Thu, 30 Sep 2021 10:12:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349778AbhI3KOX (ORCPT ); Thu, 30 Sep 2021 06:14:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:37686 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349760AbhI3KOV (ORCPT ); Thu, 30 Sep 2021 06:14:21 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0FC5F615E2; Thu, 30 Sep 2021 10:12:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1632996759; bh=02hl6AqKgati4wBU/IAmOFPWhtv3oXYR15v+gG2TMYc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=W2V1JsPXRMrZT2zTX4dsY9mFoepssR6zmCe/Qnvf0bGw7zu0vgs3/4i87OWXC0hzl 1G6BWhBvZdpD7yF5KE+VwQH2CnmTZ+UpOpMCCtzVOipragZXyDZlt3ch1+aB+9WbVk BEDOdGrPNx1l8lQlfbHBpVNSb1k8ukcFn4yOatck= Date: Thu, 30 Sep 2021 12:12:36 +0200 From: Greg Kroah-Hartman To: Ming Lei Cc: "Martin K . Petersen" , linux-scsi@vger.kernel.org, Changhui Zhong , Yi Zhang Subject: Re: [PATCH V2] scsi: core: put LLD module refcnt after SCSI device is released Message-ID: References: <20210930074026.1011114-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On Thu, Sep 30, 2021 at 04:44:07PM +0800, Ming Lei wrote: > On Thu, Sep 30, 2021 at 10:29:24AM +0200, Greg Kroah-Hartman wrote: > > On Thu, Sep 30, 2021 at 04:20:11PM +0800, Ming Lei wrote: > > > On Thu, Sep 30, 2021 at 10:07:44AM +0200, Greg Kroah-Hartman wrote: > > > > On Thu, Sep 30, 2021 at 03:40:26PM +0800, Ming Lei wrote: > > > > > SCSI host release is triggered when SCSI device is freed, and we have to > > > > > make sure that LLD module won't be unloaded before SCSI host instance is > > > > > released because shost->hostt is required in host release handler. > > > > > > > > > > So put LLD module refcnt after SCSI device is released. > > > > > > > > > > The real release handler can be run from wq context in case of > > > > > in_interrupt(), so add one atomic counter for serializing putting > > > > > module via current and wq context. This way is fine since we don't > > > > > call scsi_device_put() in fast IO path. > > > > > > > > > > Reported-by: Changhui Zhong > > > > > Reported-by: Yi Zhang > > > > > Cc: Greg Kroah-Hartman > > > > > Signed-off-by: Ming Lei > > > > > --- > > > > > drivers/scsi/scsi.c | 8 +++++++- > > > > > drivers/scsi/scsi_sysfs.c | 10 ++++++++++ > > > > > include/scsi/scsi_device.h | 2 ++ > > > > > 3 files changed, 19 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c > > > > > index b241f9e3885c..b6612161587f 100644 > > > > > --- a/drivers/scsi/scsi.c > > > > > +++ b/drivers/scsi/scsi.c > > > > > @@ -553,8 +553,14 @@ EXPORT_SYMBOL(scsi_device_get); > > > > > */ > > > > > void scsi_device_put(struct scsi_device *sdev) > > > > > { > > > > > - module_put(sdev->host->hostt->module); > > > > > + struct module *mod = sdev->host->hostt->module; > > > > > + > > > > > + atomic_inc(&sdev->put_dev_cnt); > > > > > > > > Ick, no! Why are you making a new lock and reference count for no > > > > reason? > > > > > > The reason is to make sure that the LLD module is only put from either > > > scsi_device_put() and scsi_device_dev_release_usercontext(). > > > > > > > > > > > > + > > > > > put_device(&sdev->sdev_gendev); > > > > > + > > > > > + if (atomic_dec_if_positive(&sdev->put_dev_cnt) >= 0) > > > > > + module_put(mod); > > > > > > > > How do you know if your module pointer is still valid here? > > > > > > module refcnt is grabbed in scsi_device_get(), so it is valid. > > > > Then you don't need the extra atomic variable. > > > > > > > > > > Why do you care? > > > > > > > > What problem are you trying to solve and why is it unique to scsi > > > > devices? > > > > > > See it from the commit log: > > > > > > SCSI host release is triggered when SCSI device is freed, and we have to > > > make sure that LLD module won't be unloaded before SCSI host instance is > > > released because shost->hostt is required in host release handler. > > > > What is "hostt"? > > hostt is 'struct scsi_host_template' which is defined in LLD module, and > often allocated as static global variable, that is what try_get_module() > tries to protect. > > > > > > > > > So put LLD module refcnt after SCSI device is released. > > > > Why not just drop it explicitly when you drop the reference count of the > > device object? Like you tried to do here, but no need for the extra > > atomic variable. > > scsi_device_dev_release_usercontext() may be scheduled via schedule_work from > the device object's release handler for releasing the scsi_device, which may > trigger scsi host's release handler in which hostt is required. If a release handler can be called from the device release function, then that is when you need to drop the reference, after that function is finished being called, right? thanks, greg k-h