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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 314FCC433EF for ; Thu, 21 Apr 2022 23:17:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B02716B0072; Thu, 21 Apr 2022 19:17:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AB2D96B0073; Thu, 21 Apr 2022 19:17:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 953686B0074; Thu, 21 Apr 2022 19:17:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.25]) by kanga.kvack.org (Postfix) with ESMTP id 81D8B6B0072 for ; Thu, 21 Apr 2022 19:17:34 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 4C9252021E for ; Thu, 21 Apr 2022 23:17:34 +0000 (UTC) X-FDA: 79382450028.19.9B6E26A Received: from mail-qt1-f179.google.com (mail-qt1-f179.google.com [209.85.160.179]) by imf16.hostedemail.com (Postfix) with ESMTP id 4E09618002A for ; Thu, 21 Apr 2022 23:17:32 +0000 (UTC) Received: by mail-qt1-f179.google.com with SMTP id t26so4412529qtn.6 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=G9PkQmm1n6aRt8AVXsiyU7acBgSG8HaWd+EVXZeExTqFP5pMqXiOFJYS9HqKtoVMix 5Va307NXD2Au2xfrf+Trvc54dHx+UgWjof++cVkZPE9sKzKqLkfmPiFZNcV3JfmDn/Kw u6id3BEnAEut5cxN6me9tfeh3rZ2AG7q9VuAKJIZFnix7ww/1AJQnVkd3ZmZxitx5/RC WuxtSwYGjaXkejuUHARATT6cbHPOYd5ZAopiCW0Ch3jCyBFc0yau3i47B2Sa4a5+6r53 fhxHwxqZkpozZOOJG+TF6cGh9vVVh1SitC84JgkiFMkgQfu8tVuVRtlVQZHGLHbEMDh0 6trQ== X-Gm-Message-State: AOAM533HRfjL2mOmwuTu5bQEa4VtIbs0sT3dqktSUxdpnrj4nGOBG1Ip u/b5ZepPkcnbXSS32E8icwU= 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> Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=NahulHgG; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf16.hostedemail.com: domain of yury.norov@gmail.com designates 209.85.160.179 as permitted sender) smtp.mailfrom=yury.norov@gmail.com X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 4E09618002A X-Stat-Signature: 8h643quh8o4d1pu4be3iy5a6yct4su6s X-HE-Tag: 1650583052-573626 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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