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 3B795C433F5 for ; Thu, 12 May 2022 20:54:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1358447AbiELUy6 (ORCPT ); Thu, 12 May 2022 16:54:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52412 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241316AbiELUyz (ORCPT ); Thu, 12 May 2022 16:54:55 -0400 Received: from mail-pg1-x535.google.com (mail-pg1-x535.google.com [IPv6:2607:f8b0:4864:20::535]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63580644C4 for ; Thu, 12 May 2022 13:54:53 -0700 (PDT) Received: by mail-pg1-x535.google.com with SMTP id g184so5660017pgc.1 for ; Thu, 12 May 2022 13:54:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=fgMpaknKQTL/YDwGcAjGRJjLANeCgoFIWM8w8VosUm8=; b=bKpsa0uSMKH9cKFZPdYlk+UrZykGpIXypdbdvD7uVyvrmdFEb72DetHIPcQi+/L5oX wQCKZN98KPUd63WexE4AKzrGaRNITCd9Y/2qX1q88NaLqU4R8op4R0Wf2K2c7FGe1UNV si9xLT0A+ICf9lYktfIbEXK5udUsakhMlHhTRq+9xcR1Pshcz1xMZpA1lAgvzk8xwOKq f51cZqZe5ZHQVplSZhDau3+KYMbk7sH686yCo7xRTbPo/eLe2NPUWDdMEP4Rapgo1Nzn NcDRjDhDqxSbduWcfrwRHR3RPpbLW4tA+hbnvgGbLhH9xiS7FPkFq/oZ8ZGA1640GO6h G0+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=fgMpaknKQTL/YDwGcAjGRJjLANeCgoFIWM8w8VosUm8=; b=hQX5/uRgq4Zzmu4aSMOAZ5E64ACpuUC5YkPDKdVUuDVdGAjOeLAzZoLRgWTs/yXWkt +w7RkPd1+wApfz9xLTAHoA+5ZF/wR1oi6oJ/AJRG4xKX3QH9MRSv/Q+xdZwkIk/vse8d d7XZ2IIfKlfH7XNFN98d0eiXRLDLQ3YWhSrfRuHSp7aSheG156inEDMZDCdo0s+YjKcq 2A+V54KA1Fx+92a0HHKQf+H0NCcgL9NwLfDLZ9WO7g3ZoB12QAtvjD4HRBSmEUPNumGi q5RKflN5Ys8yr9wO4ouU/BoU/NWORfF4VkPVy0BaIa3xESYF/pauSnjxL9Cey4JHTevn vO7Q== X-Gm-Message-State: AOAM532hVofyDhZv8DqrabjP9pMJqO4RHFDUpi2qTK/+z0HwtC7U+c78 AX9Y6oY6M5iwIny5Nhkj78s= X-Google-Smtp-Source: ABdhPJzHg0YPs9U5kJNFjbNV59KxzItUAZ+++S4QsjDlng5KSrRKNRdq1GjRM/ghF5ZDyJBptSdj3g== X-Received: by 2002:a05:6a00:b85:b0:510:4275:2c71 with SMTP id g5-20020a056a000b8500b0051042752c71mr1483312pfj.31.1652388892837; Thu, 12 May 2022 13:54:52 -0700 (PDT) Received: from google.com ([2620:15c:211:201:872f:bbca:8e23:fae5]) by smtp.gmail.com with ESMTPSA id n10-20020a62970a000000b0050dc762817asm248839pfe.84.2022.05.12.13.54.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 May 2022 13:54:52 -0700 (PDT) Sender: Minchan Kim Date: Thu, 12 May 2022 13:54:50 -0700 From: Minchan Kim To: John Hubbard Cc: Andrew Morton , linux-mm , LKML , "Paul E . McKenney" , John Dias , David Hildenbrand Subject: Re: [PATCH v5] mm: fix is_pinnable_page against on cma page Message-ID: References: <20220512204143.3961150-1-minchan@kernel.org> <5d9eb30e-6e0e-81a3-2b2c-47adc4e85470@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5d9eb30e-6e0e-81a3-2b2c-47adc4e85470@nvidia.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 12, 2022 at 01:51:47PM -0700, John Hubbard wrote: > On 5/12/22 13:41, Minchan Kim wrote: > > Pages on CMA area could have MIGRATE_ISOLATE as well as MIGRATE_CMA > > so current is_pinnable_page could miss CMA pages which has MIGRATE_ > > ISOLATE. It ends up pinning CMA pages as longterm at pin_user_pages > > APIs so CMA allocation keep failed until the pin is released. > > > > CPU 0 CPU 1 - Task B > > > > cma_alloc > > alloc_contig_range > > pin_user_pages_fast(FOLL_LONGTERM) > > change pageblock as MIGRATE_ISOLATE > > internal_get_user_pages_fast > > lockless_pages_from_mm > > gup_pte_range > > try_grab_folio > > is_pinnable_page > > return true; > > So, pinned the page successfully. > > page migration failure with pinned page > > .. > > .. After 30 sec > > unpin_user_page(page) > > > > CMA allocation succeeded after 30 sec. > > > > The CMA allocation path protects the migration type change race > > using zone->lock but what GUP path need to know is just whether the > > page is on CMA area or not rather than exact migration type. > > Thus, we don't need zone->lock but just checks migration type in > > either of (MIGRATE_ISOLATE and MIGRATE_CMA). > > > > Adding the MIGRATE_ISOLATE check in is_pinnable_page could cause > > rejecting of pinning pages on MIGRATE_ISOLATE pageblocks even > > though it's neither CMA nor movable zone if the page is temporarily > > unmovable. However, such a migration failure by unexpected temporal > > refcount holding is general issue, not only come from MIGRATE_ISOLATE > > and the MIGRATE_ISOLATE is also transient state like other temporal > > elevated refcount problem. > > > > Cc: "Paul E . McKenney" > > Cc: John Hubbard > > Cc: David Hildenbrand > > Signed-off-by: Minchan Kim > > --- > > * from v4 - https://lore.kernel.org/all/20220510211743.95831-1-minchan@kernel.org/ > > * clarification why we need READ_ONCE - Paul > > * Adding a comment about READ_ONCE - John > > > > * from v3 - https://lore.kernel.org/all/20220509153430.4125710-1-minchan@kernel.org/ > > * Fix typo and adding more description - akpm > > > > * from v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@kernel.org/ > > * Use __READ_ONCE instead of volatile - akpm > > > > * from v1 - https://lore.kernel.org/all/20220502173558.2510641-1-minchan@kernel.org/ > > * fix build warning - lkp > > * fix refetching issue of migration type > > * add side effect on !ZONE_MOVABLE and !MIGRATE_CMA in description - david > > > > include/linux/mm.h | 16 ++++++++++++++-- > > 1 file changed, 14 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 6acca5cecbc5..2d7a5d87decd 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -1625,8 +1625,20 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma, > > #ifdef CONFIG_MIGRATION > > static inline bool is_pinnable_page(struct page *page) > > { > > - return !(is_zone_movable_page(page) || is_migrate_cma_page(page)) || > > - is_zero_pfn(page_to_pfn(page)); > > +#ifdef CONFIG_CMA > > + /* > > + * Defend against future compiler LTO features, or code refactoring > > + * that inlines the above function, by forcing a single read. Because, > > + * this routine races with set_pageblock_migratetype(), and we want to > > + * avoid reading zero, when actually one or the other flags was set. > > + */ > > The most interesting line got dropped in this version. :) > > This is missing: > > int __mt = get_pageblock_migratetype(page); > > Assuming that that is restored, please feel free to add: > > Reviewed-by: John Hubbard Just caught after clicked the button with my fat finger :( Thanks, John! Andrew, Could you pick this up? >From 90ad049d48f5c36075f17ac996dfe3c33127aeb6 Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Mon, 2 May 2022 10:03:48 -0700 Subject: [PATCH v5] mm: fix is_pinnable_page against on cma page Pages on CMA area could have MIGRATE_ISOLATE as well as MIGRATE_CMA so current is_pinnable_page could miss CMA pages which has MIGRATE_ ISOLATE. It ends up pinning CMA pages as longterm at pin_user_pages APIs so CMA allocation keep failed until the pin is released. CPU 0 CPU 1 - Task B cma_alloc alloc_contig_range pin_user_pages_fast(FOLL_LONGTERM) change pageblock as MIGRATE_ISOLATE internal_get_user_pages_fast lockless_pages_from_mm gup_pte_range try_grab_folio is_pinnable_page return true; So, pinned the page successfully. page migration failure with pinned page .. .. After 30 sec unpin_user_page(page) CMA allocation succeeded after 30 sec. The CMA allocation path protects the migration type change race using zone->lock but what GUP path need to know is just whether the page is on CMA area or not rather than exact migration type. Thus, we don't need zone->lock but just checks migration type in either of (MIGRATE_ISOLATE and MIGRATE_CMA). Adding the MIGRATE_ISOLATE check in is_pinnable_page could cause rejecting of pinning pages on MIGRATE_ISOLATE pageblocks even though it's neither CMA nor movable zone if the page is temporarily unmovable. However, such a migration failure by unexpected temporal refcount holding is general issue, not only come from MIGRATE_ISOLATE and the MIGRATE_ISOLATE is also transient state like other temporal elevated refcount problem. Cc: "Paul E . McKenney" Cc: David Hildenbrand Reviewed-by: John Hubbard Signed-off-by: Minchan Kim --- * from v4 - https://lore.kernel.org/all/20220510211743.95831-1-minchan@kernel.org/ * clarification why we need READ_ONCE - Paul * Adding a comment about READ_ONCE - John * from v3 - https://lore.kernel.org/all/20220509153430.4125710-1-minchan@kernel.org/ * Fix typo and adding more description - akpm * from v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@kernel.org/ * Use __READ_ONCE instead of volatile - akpm * from v1 - https://lore.kernel.org/all/20220502173558.2510641-1-minchan@kernel.org/ * fix build warning - lkp * fix refetching issue of migration type * add side effect on !ZONE_MOVABLE and !MIGRATE_CMA in description - david include/linux/mm.h | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 6acca5cecbc5..b23c6f1b90b5 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1625,8 +1625,21 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma, #ifdef CONFIG_MIGRATION static inline bool is_pinnable_page(struct page *page) { - return !(is_zone_movable_page(page) || is_migrate_cma_page(page)) || - is_zero_pfn(page_to_pfn(page)); +#ifdef CONFIG_CMA + /* + * Defend against future compiler LTO features, or code refactoring + * that inlines the above function, by forcing a single read. Because, + * this routine races with set_pageblock_migratetype(), and we want to + * avoid reading zero, when actually one or the other flags was set. + */ + int __mt = get_pageblock_migratetype(page); + int mt = __READ_ONCE(__mt); + + if (mt & (MIGRATE_CMA | MIGRATE_ISOLATE)) + return false; +#endif + + return !(is_zone_movable_page(page) || is_zero_pfn(page_to_pfn(page))); } #else static inline bool is_pinnable_page(struct page *page) -- 2.36.0.550.gb090851708-goog