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=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 6941CC4727C for ; Wed, 30 Sep 2020 05:58:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CD3E206B8 for ; Wed, 30 Sep 2020 05:58:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="u7pljynD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725877AbgI3F6J (ORCPT ); Wed, 30 Sep 2020 01:58:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38930 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725440AbgI3F6I (ORCPT ); Wed, 30 Sep 2020 01:58:08 -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 8CD6AC061755; Tue, 29 Sep 2020 22:58:07 -0700 (PDT) Received: by mail-ot1-x344.google.com with SMTP id a2so668342otr.11; Tue, 29 Sep 2020 22:58:07 -0700 (PDT) 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=u/tscLGHZ4xccYrjqyEwupxAt5kBNN7tUlMMGV+ixMs=; b=u7pljynDPU40aN9yo5JU7cDXYY3oxdFJJFWREhUdTqvUzV7BApq41BPqO/4F8VR8F3 J727/JHEMb+Vk3x5ERPibcO731LZakvfIkw29WOPsPMxQLRlID0edUoRJXMXSeFA1car QTcA/m4ZEuLH6yPBNlvt2PTp+SWjmK+sjbSg58tULY0XeScSSd54yHMLl1gaub6fZwmP CgA3FUCLXkEj+BP0ih4Fm+CCyT+muMM6u9SLmmpQUFJ572IRm9MlBqJvTH9Kb2tmWi8u Sbm+nZ2gU62jQOxmsoY5YIh4UKpECx39+uCf4wV/2szLOUFdWog2fxQ/K3LqGKjYn2YJ gH2A== 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=u/tscLGHZ4xccYrjqyEwupxAt5kBNN7tUlMMGV+ixMs=; b=EpDarxsoH8+J2r9oygb4Fp1KLalSC+S3OTjDOMlarO5zlCMspasIHJm0RvC5c9QwLz GvQWs6V7piEI5TLF0LcpXwRuQbXutei1vpfI3XCXqHHNYKRbGrfIkyivXH0+CtvD6GID hx2sx3HqqsKZbng627q9oih1XPacKZNAy1g/sq24Ek1OuC16DddWARg3oMdLEU0qgEYT 9hXm9Db2gWgglKo54l+E3+KO7ZMxAFDtRknXc9/dDvNqUHs6D93fEKLdL3blezNxLeva lBg1ly+0ZR0BcHA2AEvTN1W+HoehI2ZCuJbhXjGAQWyoMYIt9DbttiBFlUXT0ZDdxUzU mTMA== X-Gm-Message-State: AOAM531Avd6NtoC6tF1i/r5IRo5zIFGMoMcjePzbEyU+UGc7de8vvWXB RYItqPsC3fdM1Osjkk2Howp/rJF9/izuldYjMkA= X-Google-Smtp-Source: ABdhPJxTN9+cQqtSYl2wkOy8mrYevlokP0ZgooKhMGz9f30W339YoQNy4jof3fuSbWBKmnzb3qYrQZlJXARscUqw0jw= X-Received: by 2002:a9d:50a:: with SMTP id 10mr524748otw.207.1601445486821; Tue, 29 Sep 2020 22:58:06 -0700 (PDT) MIME-Version: 1.0 References: <20200928131333.36646-1-mircea.caprioru@analog.com> <20200928131333.36646-4-mircea.caprioru@analog.com> <20200929171441.5b4ff8c8@archlinux> In-Reply-To: <20200929171441.5b4ff8c8@archlinux> From: Alexandru Ardelean Date: Wed, 30 Sep 2020 08:57:55 +0300 Message-ID: Subject: Re: [PATCH 4/5] iio: adc: vf610_adc: Replace indio_dev->mlock with own device lock To: Jonathan Cameron Cc: Mircea Caprioru , "Hennerich, Michael" , Alexandru Ardelean , Lars-Peter Clausen , Greg Kroah-Hartman , LKML , linux-iio , Sergiu Cuciurean Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 29, 2020 at 7:15 PM Jonathan Cameron wrote: > > On Mon, 28 Sep 2020 16:13:32 +0300 > Mircea Caprioru wrote: > > > From: Sergiu Cuciurean > > > > As part of the general cleanup of indio_dev->mlock, this change replaces > > it with a local lock on the device's state structure. > > > > This is part of a bigger cleanup. > > Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@mail.gmail.com/ > > > > Signed-off-by: Sergiu Cuciurean > > Signed-off-by: Mircea Caprioru > > There are more problems in the locking in here than just this one. > See below. The taking of mlock like this was what originally motivated > the efforts to hide it away from drivers. > > In this particular case I don't think a local lock is the correct solution. > > Thanks, > > Jonathan > > > > --- > > drivers/iio/adc/vf610_adc.c | 28 ++++++++++++++++++++-------- > > 1 file changed, 20 insertions(+), 8 deletions(-) > > > > diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c > > index 1d794cf3e3f1..b7d583993f0b 100644 > > --- a/drivers/iio/adc/vf610_adc.c > > +++ b/drivers/iio/adc/vf610_adc.c > > @@ -168,6 +168,15 @@ struct vf610_adc { > > > > struct completion completion; > > u16 buffer[8]; > > Side note. That buffer isn't correctly aligned. I'll add this one to > my next series fixing those. > > > + /* > > + * Lock to protect the device state during a potential concurrent > > + * read access from userspace. Reading a raw value requires a sequence > > + * of register writes, then a wait for a completion callback, > > + * and finally a register read, during which userspace could issue > > + * another read request. This lock protects a read access from > > + * ocurring before another one has finished. > > + */ > > + struct mutex lock; > > }; > > > > static const u32 vf610_hw_avgs[] = { 1, 4, 8, 16, 32 }; > > @@ -464,11 +473,11 @@ static int vf610_set_conversion_mode(struct iio_dev *indio_dev, > > { > > struct vf610_adc *info = iio_priv(indio_dev); > > > > - mutex_lock(&indio_dev->mlock); > > + mutex_lock(&info->lock); > Hmm. So there is a bit of a question on what the locking here is doing. > (see below for a different use of mlock). > > What it will do currently is to prevent the conversion mode changing whilst > we are in buffered mode. It will also protect against concurrent > calls of this function. > > I would replace this with iio_device_claim_direct_mode() rather than a > local lock. This raises a new question: if there's any drivers that we missed [for iio_device_claim_direct_mode()]. While I was aware of iio_device_claim_direct_mode(), I missed this fact when pushing the mlock cleanup. Oh well, I'll do a quick audit over the current drivers that were converted. Hopefully I don't find anything :P > > > info->adc_feature.conv_mode = mode; > > vf610_adc_calculate_rates(info); > > vf610_adc_hw_init(info); > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > > > return 0; > > } > > @@ -632,9 +641,9 @@ static int vf610_read_raw(struct iio_dev *indio_dev, > > switch (mask) { > > case IIO_CHAN_INFO_RAW: > > case IIO_CHAN_INFO_PROCESSED: > > - mutex_lock(&indio_dev->mlock); > > + mutex_lock(&info->lock); > > if (iio_buffer_enabled(indio_dev)) { > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > Should be use iio_device_claim_direct_mode() > > mlock is being taken here to stop us entering buffered mode. > > Whilst I'd rather a driver didn't rely on internal details of > IIO, it is rather fiddly to get the locking right when there is a completion > going on, so I think here you are safe to do so. > > > return -EBUSY; > > } > > > > @@ -645,11 +654,11 @@ static int vf610_read_raw(struct iio_dev *indio_dev, > > ret = wait_for_completion_interruptible_timeout > > (&info->completion, VF610_ADC_TIMEOUT); > > if (ret == 0) { > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > return -ETIMEDOUT; > > } > > if (ret < 0) { > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > return ret; > > } > > > > @@ -668,11 +677,11 @@ static int vf610_read_raw(struct iio_dev *indio_dev, > > > > break; > > default: > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > return -EINVAL; > > } > > > > - mutex_unlock(&indio_dev->mlock); > > + mutex_unlock(&info->lock); > > return IIO_VAL_INT; > > > > case IIO_CHAN_INFO_SCALE: > > @@ -807,6 +816,9 @@ static int vf610_adc_probe(struct platform_device *pdev) > > } > > > > info = iio_priv(indio_dev); > > + > > + mutex_init(&info->lock); > > + > > info->dev = &pdev->dev; > > > > info->regs = devm_platform_ioremap_resource(pdev, 0); >