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 C35DAC433EF for ; Thu, 21 Apr 2022 23:17:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1442245AbiDUXU1 (ORCPT ); Thu, 21 Apr 2022 19:20:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59288 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1442211AbiDUXUZ (ORCPT ); Thu, 21 Apr 2022 19:20:25 -0400 Received: from mail-qt1-x82f.google.com (mail-qt1-x82f.google.com [IPv6:2607:f8b0:4864:20::82f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F20EC3982A for ; Thu, 21 Apr 2022 16:17:33 -0700 (PDT) Received: by mail-qt1-x82f.google.com with SMTP id hh4so4398359qtb.10 for ; Thu, 21 Apr 2022 16:17:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=4De3YRMK1Ra85Dips/fnb0PQnHGIx9mJCfq1fssj8tg=; b=NahulHgG7AbSSsGtdussdVQis65kI8sp5gMXA41OPT6pGnY/J/4EzAjaq/y77Z2HXw aOv8oX2SNChMWUOv81wt0xVJAtxuYfbsKco7GTIoFywSROonMW44bI6fESBxGV9tOLK+ UJn1uFBSDVlSTXnBKxF7bxejGfuT0CVDlHE621+N2rH5vB8GlOuXKG5EkttdqR13qkzz WI3U2fkUUuKIl78IFOFSjcdHQ3fw5oeGRtBpoFuen9BPAmdpacd2Kpm4m7ae9F2WjcEO q78IrsC2YKd/NF8fUonEGoD5HYSfshBpzLSn4KwAiBYkzCl425g/dqC+zk+lRn0x99so GlEA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=4De3YRMK1Ra85Dips/fnb0PQnHGIx9mJCfq1fssj8tg=; b=tbkUuHTSYTTJ9v6ex4KMq1EuDTP0czKud3AYRjDLrOey+R6OdRrXDeFfD6KQcPwB3k FnG4ZkuGOHGf66l/X1Mp8iCAjWwRDD8RIQ3LWA4FZVNDaeVR9/IyW7H+kIULtJMl/fgL W6IIhi09sOgXQ++uqzN1HrtFPn2zpGKS/eb+b5mE7tSY81k5VRksO2Lh+73Gbr9NEv+Y kASWNiukgWdCgMOrz5rXhjQq/gwqNGzvMYLfBZx6BrSycdKzrzC3X+5mBXLz4fxS2TVn g/z6y8KoSTlutxlwC3J2d42NGYT1qliag+ruQ2f4Rx+XG9BS9aQ+/qW7R2gBV6mdZ0VP Ntrg== X-Gm-Message-State: AOAM533ac0xWAAqNO/AF3NT89gF5a2ewmUJMhn2VQ4E+eBqYXKdgZ/4i dGmgtcLCT5toi61SkdXnUIo= X-Google-Smtp-Source: ABdhPJyYbA/4NtfvAf2c391c2gmRt86bly6dOI/e0Wpz6xRjKeXrAL0qHq6/hcVKXFRdCyqGe1zvXQ== X-Received: by 2002:ac8:7c4e:0:b0:2f3:365b:54d3 with SMTP id o14-20020ac87c4e000000b002f3365b54d3mr1358438qtv.37.1650583052958; Thu, 21 Apr 2022 16:17:32 -0700 (PDT) Received: from localhost ([2601:c4:c432:668:da50:5094:8aba:8f5e]) by smtp.gmail.com with ESMTPSA id x20-20020ac85f14000000b002e1ee1c56c3sm265322qta.76.2022.04.21.16.17.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Apr 2022 16:17:32 -0700 (PDT) Date: Thu, 21 Apr 2022 16:17:31 -0700 From: Yury Norov To: John Hubbard Cc: Andrew Morton , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: Message-ID: References: <20220421164138.1250943-1-yury.norov@gmail.com> <92a2715c-3c98-251d-9195-872d1cf01f9d@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <92a2715c-3c98-251d-9195-872d1cf01f9d@nvidia.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 21, 2022 at 04:04:44PM -0700, John Hubbard wrote: > On 4/21/22 09:41, Yury Norov wrote: > > Subject: [PATCH] mm/gup: fix comments to pin_user_pages_*() > > > > Hi Yuri, > > Thanks for picking this up. I have been distracted and didn't trust > myself to focus on this properly, so it's good to have help! > > IT/admin point: somehow the first line of the commit description didn't > make it into an actual email subject. The subject line was blank when it > arrived in my inbox, and the subject is in the body here instead. Not > sure how that happened. > > Maybe check your git-sendemail setup? git-sendmail is OK. I just accidentally added empty line above Subject, which broke format. My bad, sorry for this. > > pin_user_pages API forces FOLL_PIN in gup_flags, which means that the > > API requires struct page **pages to be provided (not NULL). However, > > the comment to pin_user_pages() says: > > > > * @pages: array that receives pointers to the pages pinned. > > * Should be at least nr_pages long. Or NULL, if caller > > * only intends to ensure the pages are faulted in. > > > > This patch fixes comments along the pin_user_pages code, and also adds > > WARN_ON(!pages), so that API users will have better understanding > > on how to use it. > > No need to quote the code in the commit log. Instead, just summarize. > For example: > > pin_user_pages API forces FOLL_PIN in gup_flags, which means that the > API requires struct page **pages to be provided (not NULL). However, the > comment to pin_user_pages() clearly allows for passing in a NULL @pages > argument. > > Remove the incorrect comments, and add WARN_ON_ONCE(!pages) calls to > enforce the API. > > > > > It has been independently spotted by Minchan Kim and confirmed with > > John Hubbard: > > > > https://lore.kernel.org/all/YgWA0ghrrzHONehH@google.com/ > > Let's add a Cc: line for Michan as well: > > Cc: Minchan Kim He's in CC already, I think... > > Signed-off-by: Yury Norov (NVIDIA) > > --- > > mm/gup.c | 26 ++++++++++++++++++++++---- > > 1 file changed, 22 insertions(+), 4 deletions(-) > > > > diff --git a/mm/gup.c b/mm/gup.c > > index f598a037eb04..559626457585 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -2871,6 +2871,10 @@ int pin_user_pages_fast(unsigned long start, int nr_pages, > > if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > > return -EINVAL; > > + /* FOLL_PIN requires pages != NULL */ > > Please delete each and every one of these one-line comments, because > they merely echo what the code says. Sure. > > + if (WARN_ON_ONCE(!pages)) > > + return -EINVAL; > > + > > gup_flags |= FOLL_PIN; > > return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); > > } > > @@ -2893,6 +2897,10 @@ int pin_user_pages_fast_only(unsigned long start, int nr_pages, > > */ > > if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > > return 0; > > + > > + /* FOLL_PIN requires pages != NULL */ > > + if (WARN_ON_ONCE(!pages)) > > + return 0; > > /* > > * FOLL_FAST_ONLY is required in order to match the API description of > > * this routine: no fall back to regular ("slow") GUP. > > @@ -2920,8 +2928,7 @@ EXPORT_SYMBOL_GPL(pin_user_pages_fast_only); > > * @nr_pages: number of pages from start to pin > > * @gup_flags: flags modifying lookup behaviour > > * @pages: array that receives pointers to the pages pinned. > > - * Should be at least nr_pages long. Or NULL, if caller > > - * only intends to ensure the pages are faulted in. > > + * Should be at least nr_pages long. > > * @vmas: array of pointers to vmas corresponding to each page. > > * Or NULL if the caller does not require them. > > * @locked: pointer to lock flag indicating whether lock is held and > > @@ -2944,6 +2951,10 @@ long pin_user_pages_remote(struct mm_struct *mm, > > if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > > return -EINVAL; > > + /* FOLL_PIN requires pages != NULL */ > > + if (WARN_ON_ONCE(!pages)) > > + return -EINVAL; > > + > > gup_flags |= FOLL_PIN; > > return __get_user_pages_remote(mm, start, nr_pages, gup_flags, > > pages, vmas, locked); > > @@ -2957,8 +2968,7 @@ EXPORT_SYMBOL(pin_user_pages_remote); > > * @nr_pages: number of pages from start to pin > > * @gup_flags: flags modifying lookup behaviour > > * @pages: array that receives pointers to the pages pinned. > > - * Should be at least nr_pages long. Or NULL, if caller > > - * only intends to ensure the pages are faulted in. > > + * Should be at least nr_pages long. > > * @vmas: array of pointers to vmas corresponding to each page. > > * Or NULL if the caller does not require them. > > * > > @@ -2976,6 +2986,10 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages, > > if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > > return -EINVAL; > > + /* FOLL_PIN requires pages != NULL */ > > + if (WARN_ON_ONCE(!pages)) > > + return -EINVAL; > > + > > gup_flags |= FOLL_PIN; > > return __gup_longterm_locked(current->mm, start, nr_pages, > > pages, vmas, gup_flags); > > @@ -2994,6 +3008,10 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > > if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > > return -EINVAL; > > + /* FOLL_PIN requires pages != NULL */ > > + if (WARN_ON_ONCE(!pages)) > > + return -EINVAL; > > + > > gup_flags |= FOLL_PIN; > > return get_user_pages_unlocked(start, nr_pages, pages, gup_flags); > > } > > I hope we don't break any callers with the newly enforced !pages, but it's > the right thing to do, in order to avoid misunderstandings. > > thanks, > -- > John Hubbard > NVIDIA Let me test v2 and resend shortly. Thanks, Yury