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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 AF150C433FE for ; Thu, 10 Dec 2020 10:45:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1AE5523D69 for ; Thu, 10 Dec 2020 10:45:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1AE5523D69 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 22D896B0036; Thu, 10 Dec 2020 05:45:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1B5956B005D; Thu, 10 Dec 2020 05:45:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0A49A6B0068; Thu, 10 Dec 2020 05:45:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0207.hostedemail.com [216.40.44.207]) by kanga.kvack.org (Postfix) with ESMTP id EDEA16B0036 for ; Thu, 10 Dec 2020 05:45:32 -0500 (EST) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id CCCF98249980 for ; Thu, 10 Dec 2020 10:45:32 +0000 (UTC) X-FDA: 77577041304.20.sofa16_4712864273f7 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin20.hostedemail.com (Postfix) with ESMTP id A8229180C07AF for ; Thu, 10 Dec 2020 10:45:32 +0000 (UTC) X-HE-Tag: sofa16_4712864273f7 X-Filterd-Recvd-Size: 7264 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Thu, 10 Dec 2020 10:45:31 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 0E3FEAF31; Thu, 10 Dec 2020 10:39:00 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 302351E0F6A; Thu, 10 Dec 2020 10:22:40 +0100 (CET) Date: Thu, 10 Dec 2020 10:22:40 +0100 From: Jan Kara To: Jason Gunthorpe Cc: Andrew Morton , John Hubbard , Joao Martins , linux-mm , Jonathan Corbet , Dan Williams , Dave Chinner , Christoph Hellwig , Ira Weiny , Jan Kara , Jane Chu , "Kirill A. Shutemov" , linux-nvdimm@lists.01.org, Michal Hocko , Mike Kravetz , Shuah Khan , Muchun Song , Vlastimil Babka , Matthew Wilcox Subject: Re: [PATCH] mm/up: combine put_compound_head() and unpin_user_page() Message-ID: <20201210092240.GA24151@quack2.suse.cz> References: <0-v1-6730d4ee0d32+40e6-gup_combine_put_jgg@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0-v1-6730d4ee0d32+40e6-gup_combine_put_jgg@nvidia.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Wed 09-12-20 15:13:57, Jason Gunthorpe wrote: > These functions accomplish the same thing but have different > implementations. > > unpin_user_page() has a bug where it calls mod_node_page_state() after > calling put_page() which creates a risk that the page could have been > hot-uplugged from the system. > > Fix this by using put_compound_head() as the only implementation. > > __unpin_devmap_managed_user_page() and related can be deleted as well in > favour of the simpler, but slower, version in put_compound_head() that has > an extra atomic page_ref_sub, but always calls put_page() which internally > contains the special devmap code. > > Move put_compound_head() to be directly after try_grab_compound_head() so > people can find it in future. > > Fixes: 1970dc6f5226 ("mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting") > Signed-off-by: Jason Gunthorpe Nice cleanup. The patch looks good to me. You can add: Reviewed-by: Jan Kara Honza > --- > mm/gup.c | 103 +++++++++++++------------------------------------------ > 1 file changed, 23 insertions(+), 80 deletions(-) > > With Matt's folio idea I'd next to go to make a > put_folio(folio, refs) > > Which would cleanly eliminate that extra atomic here without duplicating the > devmap special case. > > This should also be called 'ungrab_compound_head' as we seem to be using the > word 'grab' to mean 'pin or get' depending on GUP flags. > > diff --git a/mm/gup.c b/mm/gup.c > index 98eb8e6d2609c3..7b33b7d4b324d7 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -123,6 +123,28 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page, > return NULL; > } > > +static void put_compound_head(struct page *page, int refs, unsigned int flags) > +{ > + if (flags & FOLL_PIN) { > + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, > + refs); > + > + if (hpage_pincount_available(page)) > + hpage_pincount_sub(page, refs); > + else > + refs *= GUP_PIN_COUNTING_BIAS; > + } > + > + VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); > + /* > + * Calling put_page() for each ref is unnecessarily slow. Only the last > + * ref needs a put_page(). > + */ > + if (refs > 1) > + page_ref_sub(page, refs - 1); > + put_page(page); > +} > + > /** > * try_grab_page() - elevate a page's refcount by a flag-dependent amount > * > @@ -177,41 +199,6 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags) > return true; > } > > -#ifdef CONFIG_DEV_PAGEMAP_OPS > -static bool __unpin_devmap_managed_user_page(struct page *page) > -{ > - int count, refs = 1; > - > - if (!page_is_devmap_managed(page)) > - return false; > - > - if (hpage_pincount_available(page)) > - hpage_pincount_sub(page, 1); > - else > - refs = GUP_PIN_COUNTING_BIAS; > - > - count = page_ref_sub_return(page, refs); > - > - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1); > - /* > - * devmap page refcounts are 1-based, rather than 0-based: if > - * refcount is 1, then the page is free and the refcount is > - * stable because nobody holds a reference on the page. > - */ > - if (count == 1) > - free_devmap_managed_page(page); > - else if (!count) > - __put_page(page); > - > - return true; > -} > -#else > -static bool __unpin_devmap_managed_user_page(struct page *page) > -{ > - return false; > -} > -#endif /* CONFIG_DEV_PAGEMAP_OPS */ > - > /** > * unpin_user_page() - release a dma-pinned page > * @page: pointer to page to be released > @@ -223,28 +210,7 @@ static bool __unpin_devmap_managed_user_page(struct page *page) > */ > void unpin_user_page(struct page *page) > { > - int refs = 1; > - > - page = compound_head(page); > - > - /* > - * For devmap managed pages we need to catch refcount transition from > - * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the > - * page is free and we need to inform the device driver through > - * callback. See include/linux/memremap.h and HMM for details. > - */ > - if (__unpin_devmap_managed_user_page(page)) > - return; > - > - if (hpage_pincount_available(page)) > - hpage_pincount_sub(page, 1); > - else > - refs = GUP_PIN_COUNTING_BIAS; > - > - if (page_ref_sub_and_test(page, refs)) > - __put_page(page); > - > - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1); > + put_compound_head(compound_head(page), 1, FOLL_PIN); > } > EXPORT_SYMBOL(unpin_user_page); > > @@ -2062,29 +2028,6 @@ EXPORT_SYMBOL(get_user_pages_unlocked); > * This code is based heavily on the PowerPC implementation by Nick Piggin. > */ > #ifdef CONFIG_HAVE_FAST_GUP > - > -static void put_compound_head(struct page *page, int refs, unsigned int flags) > -{ > - if (flags & FOLL_PIN) { > - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, > - refs); > - > - if (hpage_pincount_available(page)) > - hpage_pincount_sub(page, refs); > - else > - refs *= GUP_PIN_COUNTING_BIAS; > - } > - > - VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); > - /* > - * Calling put_page() for each ref is unnecessarily slow. Only the last > - * ref needs a put_page(). > - */ > - if (refs > 1) > - page_ref_sub(page, refs - 1); > - put_page(page); > -} > - > #ifdef CONFIG_GUP_GET_PTE_LOW_HIGH > > /* > -- > 2.29.2 > -- Jan Kara SUSE Labs, CR