From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Hubbard Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions Date: Mon, 14 Jan 2019 11:09:20 -0800 Message-ID: References: <20190103092654.GA31370@quack2.suse.cz> <20190103144405.GC3395@redhat.com> <20190111165141.GB3190@redhat.com> <1b37061c-5598-1b02-2983-80003f1c71f2@nvidia.com> <20190112020228.GA5059@redhat.com> <294bdcfa-5bf9-9c09-9d43-875e8375e264@nvidia.com> <20190112024625.GB5059@redhat.com> <20190114145447.GJ13316@quack2.suse.cz> <20190114172124.GA3702@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: Matthew Wilcox , Dave Chinner , Dan Williams , John Hubbard , Andrew Morton , Linux MM , , Al Viro , , Christoph Hellwig , Christopher Lameter , "Dalessandro, Dennis" , Doug Ledford , Jason Gunthorpe , Michal Hocko , , , Linux Kernel Mailing List , linux-fsdevel To: Jerome Glisse , Jan Kara Return-path: In-Reply-To: <20190114172124.GA3702@redhat.com> Content-Language: en-US-large Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On 1/14/19 9:21 AM, Jerome Glisse wrote: > On Mon, Jan 14, 2019 at 03:54:47PM +0100, Jan Kara wrote: >> On Fri 11-01-19 19:06:08, John Hubbard wrote: >>> On 1/11/19 6:46 PM, Jerome Glisse wrote: >>>> On Fri, Jan 11, 2019 at 06:38:44PM -0800, John Hubbard wrote: >>>> [...] >>>> >>>>>>> The other idea that you and Dan (and maybe others) pointed out was a debug >>>>>>> option, which we'll certainly need in order to safely convert all the call >>>>>>> sites. (Mirror the mappings at a different kernel offset, so that put_page() >>>>>>> and put_user_page() can verify that the right call was made.) That will be >>>>>>> a separate patchset, as you recommended. >>>>>>> >>>>>>> I'll even go as far as recommending the page lock itself. I realize that this >>>>>>> adds overhead to gup(), but we *must* hold off page_mkclean(), and I believe >>>>>>> that this (below) has similar overhead to the notes above--but is *much* easier >>>>>>> to verify correct. (If the page lock is unacceptable due to being so widely used, >>>>>>> then I'd recommend using another page bit to do the same thing.) >>>>>> >>>>>> Please page lock is pointless and it will not work for GUP fast. The above >>>>>> scheme do work and is fine. I spend the day again thinking about all memory >>>>>> ordering and i do not see any issues. >>>>>> >>>>> >>>>> Why is it that page lock cannot be used for gup fast, btw? >>>> >>>> Well it can not happen within the preempt disable section. But after >>>> as a post pass before GUP_fast return and after reenabling preempt then >>>> it is fine like it would be for regular GUP. But locking page for GUP >>>> is also likely to slow down some workload (with direct-IO). >>>> >>> >>> Right, and so to crux of the matter: taking an uncontended page lock >>> involves pretty much the same set of operations that your approach does. >>> (If gup ends up contended with the page lock for other reasons than these >>> paths, that seems surprising.) I'd expect very similar performance. >>> >>> But the page lock approach leads to really dramatically simpler code (and >>> code reviews, let's not forget). Any objection to my going that >>> direction, and keeping this idea as a Plan B? I think the next step will >>> be, once again, to gather some performance metrics, so maybe that will >>> help us decide. >> >> FWIW I agree that using page lock for protecting page pinning (and thus >> avoid races with page_mkclean()) looks simpler to me as well and I'm not >> convinced there will be measurable difference to the more complex scheme >> with barriers Jerome suggests unless that page lock contended. Jerome is >> right that you cannot just do lock_page() in gup_fast() path. There you >> have to do trylock_page() and if that fails just bail out to the slow gup >> path. >> Yes, understood about gup fast. >> Regarding places other than page_mkclean() that need to check pinned state: >> Definitely page migration will want to check whether the page is pinned or >> not so that it can deal differently with short-term page references vs >> longer-term pins. OK. >> >> Also there is one more idea I had how to record number of pins in the page: >> >> #define PAGE_PIN_BIAS 1024 >> >> get_page_pin() >> atomic_add(&page->_refcount, PAGE_PIN_BIAS); >> >> put_page_pin(); >> atomic_add(&page->_refcount, -PAGE_PIN_BIAS); >> >> page_pinned(page) >> (atomic_read(&page->_refcount) - page_mapcount(page)) > PAGE_PIN_BIAS >> >> This is pretty trivial scheme. It still gives us 22-bits for page pins >> which should be plenty (but we should check for that and bail with error if >> it would overflow). Also there will be no false negatives and false >> positives only if there are more than 1024 non-page-table references to the >> page which I expect to be rare (we might want to also subtract >> hpage_nr_pages() for radix tree references to avoid excessive false >> positives for huge pages although at this point I don't think they would >> matter). Thoughts? > > Racing PUP are as likely to cause issues: > > CPU0 | CPU1 | CPU2 > | | > | PUP() | > page_pinned(page) | | > (page_count(page) - | | > page_mapcount(page)) | | > | | GUP() > > So here the refcount snap-shot does not include the second GUP and > we can have a false negative ie the page_pinned() will return false > because of the PUP happening just before on CPU1 despite the racing > GUP on CPU2 just after. > > I believe only either lock or memory ordering with barrier can > guarantee that we do not miss GUP ie no false negative. Still the > bias idea might be usefull as with it we should not need a flag. > > So to make the above safe it would still need the page write back > double check that i described so that GUP back-off if it raced with > page_mkclean,clear_page_dirty_for_io and the fs write page call back > which call test_set_page_writeback() (yes it is very unlikely but > might still happen). > > > I still need to ponder some more on all the races. > Tentatively, so far I prefer the _mapcount scheme, because it seems more accurate to add mapcounts than to overload the _refcount field. And the implementation is going to be cleaner. And we've already figured out the races. For example, the following already survives a basic boot to graphics mode. It requires a bunch of callsite conversions, and a page flag (neither of which is shown here), and may also have "a few" gross conceptual errors, but take a peek: >>From 1b6e611238a45badda7e63d3ffc089cefb621cb2 Mon Sep 17 00:00:00 2001 From: John Hubbard Date: Sun, 13 Jan 2019 15:10:31 -0800 Subject: [PATCH 2/2] mm: track gup-pinned pages X-NVConfidentiality: public Cc: John Hubbard Track GUP-pinned pages. Signed-off-by: John Hubbard --- include/linux/mm.h | 8 ++++--- mm/gup.c | 59 +++++++++++++++++++++++++++++++++++++++++++--- mm/rmap.c | 23 ++++++++++++++---- 3 files changed, 79 insertions(+), 11 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 809b7397d41e..3221a13b4891 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1004,12 +1004,14 @@ static inline void put_page(struct page *page) * particular, interactions with RDMA and filesystems need special * handling. * - * put_user_page() and put_page() are not interchangeable, despite this early - * implementation that makes them look the same. put_user_page() calls must - * be perfectly matched up with get_user_page() calls. + * put_user_page() and put_page() are not interchangeable. put_user_page() + * calls must be perfectly matched up with get_user_page() calls. */ static inline void put_user_page(struct page *page) { + page = compound_head(page); + + atomic_dec(&page->_mapcount); put_page(page); } diff --git a/mm/gup.c b/mm/gup.c index 05acd7e2eb22..af3909814be7 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -615,6 +615,48 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) return 0; } +/* + * Manages the PG_gup_pinned flag. + * + * Note that page->_mapcount counting part of managing that flag, because the + * _mapcount is used to determine if PG_gup_pinned can be cleared, in + * page_mkclean(). + */ +static void track_gup_page(struct page *page) +{ + page = compound_head(page); + + lock_page(page); + + wait_on_page_writeback(page); + + atomic_inc(&page->_mapcount); + SetPageGupPinned(page); + + unlock_page(page); +} + +/* + * A variant of track_gup_page() that returns -EBUSY, instead of waiting. + */ +static int track_gup_page_atomic(struct page *page) +{ + page = compound_head(page); + + if (PageWriteback(page) || !trylock_page(page)) + return -EBUSY; + + if (PageWriteback(page)) { + unlock_page(page); + return -EBUSY; + } + atomic_inc(&page->_mapcount); + SetPageGupPinned(page); + + unlock_page(page); + return 0; +} + /** * __get_user_pages() - pin user pages in memory * @tsk: task_struct of target task @@ -761,6 +803,9 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, ret = PTR_ERR(page); goto out; } + + track_gup_page(page); + if (pages) { pages[i] = page; flush_anon_page(vma, page, start); @@ -1439,6 +1484,11 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, VM_BUG_ON_PAGE(compound_head(page) != head, page); + if (track_gup_page_atomic(page)) { + put_page(head); + goto pte_unmap; + } + SetPageReferenced(page); pages[*nr] = page; (*nr)++; @@ -1574,7 +1624,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, return 0; } - if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { + if (unlikely(pmd_val(orig) != pmd_val(*pmdp)) || + track_gup_page_atomic(head)) { *nr -= refs; while (refs--) put_page(head); @@ -1612,7 +1663,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, return 0; } - if (unlikely(pud_val(orig) != pud_val(*pudp))) { + if (unlikely(pud_val(orig) != pud_val(*pudp)) || + track_gup_page_atomic(head)) { *nr -= refs; while (refs--) put_page(head); @@ -1649,7 +1701,8 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, return 0; } - if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) { + if (unlikely(pgd_val(orig) != pgd_val(*pgdp)) || + track_gup_page_atomic(head)) { *nr -= refs; while (refs--) put_page(head); diff --git a/mm/rmap.c b/mm/rmap.c index 0454ecc29537..434283898bb0 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -880,6 +880,11 @@ int page_referenced(struct page *page, return pra.referenced; } +struct page_mkclean_args { + int cleaned; + int mapcount; +}; + static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, unsigned long address, void *arg) { @@ -890,7 +895,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, .flags = PVMW_SYNC, }; struct mmu_notifier_range range; - int *cleaned = arg; + struct page_mkclean_args *pma = arg; /* * We have to assume the worse case ie pmd for invalidation. Note that @@ -940,6 +945,8 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, #endif } + pma->mapcount++; + /* * No need to call mmu_notifier_invalidate_range() as we are * downgrading page table protection not changing it to point @@ -948,7 +955,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, * See Documentation/vm/mmu_notifier.rst */ if (ret) - (*cleaned)++; + pma->cleaned++; } mmu_notifier_invalidate_range_end(&range); @@ -966,10 +973,13 @@ static bool invalid_mkclean_vma(struct vm_area_struct *vma, void *arg) int page_mkclean(struct page *page) { - int cleaned = 0; + struct page_mkclean_args pma = { + .cleaned = 0, + .mapcount = 0 + }; struct address_space *mapping; struct rmap_walk_control rwc = { - .arg = (void *)&cleaned, + .arg = (void *)&pma, .rmap_one = page_mkclean_one, .invalid_vma = invalid_mkclean_vma, }; @@ -985,7 +995,10 @@ int page_mkclean(struct page *page) rmap_walk(page, &rwc); - return cleaned; + if (pma.mapcount == page_mapcount(page)) + ClearPageGupPinned(page); + + return pma.cleaned; } EXPORT_SYMBOL_GPL(page_mkclean); -- 2.20.1 thanks, -- John Hubbard NVIDIA 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=-7.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 25893C43444 for ; Mon, 14 Jan 2019 19:09:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D5B5220659 for ; Mon, 14 Jan 2019 19:09:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="m2uNk6dL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726758AbfANTJ0 (ORCPT ); Mon, 14 Jan 2019 14:09:26 -0500 Received: from hqemgate14.nvidia.com ([216.228.121.143]:17804 "EHLO hqemgate14.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726643AbfANTJZ (ORCPT ); Mon, 14 Jan 2019 14:09:25 -0500 Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqemgate14.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Mon, 14 Jan 2019 11:09:07 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Mon, 14 Jan 2019 11:09:21 -0800 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Mon, 14 Jan 2019 11:09:21 -0800 Received: from [10.110.48.28] (10.124.1.5) by HQMAIL101.nvidia.com (172.20.187.10) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Mon, 14 Jan 2019 19:09:21 +0000 Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions To: Jerome Glisse , Jan Kara CC: Matthew Wilcox , Dave Chinner , Dan Williams , John Hubbard , Andrew Morton , Linux MM , , Al Viro , , Christoph Hellwig , Christopher Lameter , "Dalessandro, Dennis" , Doug Ledford , Jason Gunthorpe , Michal Hocko , , , Linux Kernel Mailing List , linux-fsdevel References: <20190103092654.GA31370@quack2.suse.cz> <20190103144405.GC3395@redhat.com> <20190111165141.GB3190@redhat.com> <1b37061c-5598-1b02-2983-80003f1c71f2@nvidia.com> <20190112020228.GA5059@redhat.com> <294bdcfa-5bf9-9c09-9d43-875e8375e264@nvidia.com> <20190112024625.GB5059@redhat.com> <20190114145447.GJ13316@quack2.suse.cz> <20190114172124.GA3702@redhat.com> X-Nvconfidentiality: public From: John Hubbard Message-ID: Date: Mon, 14 Jan 2019 11:09:20 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190114172124.GA3702@redhat.com> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL101.nvidia.com (172.20.187.10) Content-Type: text/plain; charset="utf-8" Content-Language: en-US-large Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1547492947; bh=rZtJhh0vCOrPh5Z9XADf58DeD2/uNzjSHU5sr1L08tQ=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=m2uNk6dLaQLzyP25r7JJSiIqXJP52IFuJhjJqASwCwpiSf2XDxHZOfoVZDTchczWu gdCKYHmyGjo3+Xc1nEEkOmYhIT0untw6vzTZ/9iRVZtP3Xb2yrsjrssRRz56Op3FjP Egt+xLR4Ck/HaJ0NXpBwzplBtF3/2odLbRsV/cYZAkR5eJVG9uMMCYyRTdNik4V+MJ c54WAeow4jr1xzCSTrYay9SYoP86VG/ft3KHPT+Dnr1T124t346rWJSnSZKmLqPOD3 ZzLi7r9ifT92XuAZdUErIpkp/pFrbPWD9BbhKKX8s9EZMFWhKv35Tz0r08IGhs5n4H HBe6uQ0/6KKUg== Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Message-ID: <20190114190920.JznZCMPFbvxD98eaxGYEqZyfmKWeOQfpgfb1k5ygkFA@z> On 1/14/19 9:21 AM, Jerome Glisse wrote: > On Mon, Jan 14, 2019 at 03:54:47PM +0100, Jan Kara wrote: >> On Fri 11-01-19 19:06:08, John Hubbard wrote: >>> On 1/11/19 6:46 PM, Jerome Glisse wrote: >>>> On Fri, Jan 11, 2019 at 06:38:44PM -0800, John Hubbard wrote: >>>> [...] >>>> >>>>>>> The other idea that you and Dan (and maybe others) pointed out was a debug >>>>>>> option, which we'll certainly need in order to safely convert all the call >>>>>>> sites. (Mirror the mappings at a different kernel offset, so that put_page() >>>>>>> and put_user_page() can verify that the right call was made.) That will be >>>>>>> a separate patchset, as you recommended. >>>>>>> >>>>>>> I'll even go as far as recommending the page lock itself. I realize that this >>>>>>> adds overhead to gup(), but we *must* hold off page_mkclean(), and I believe >>>>>>> that this (below) has similar overhead to the notes above--but is *much* easier >>>>>>> to verify correct. (If the page lock is unacceptable due to being so widely used, >>>>>>> then I'd recommend using another page bit to do the same thing.) >>>>>> >>>>>> Please page lock is pointless and it will not work for GUP fast. The above >>>>>> scheme do work and is fine. I spend the day again thinking about all memory >>>>>> ordering and i do not see any issues. >>>>>> >>>>> >>>>> Why is it that page lock cannot be used for gup fast, btw? >>>> >>>> Well it can not happen within the preempt disable section. But after >>>> as a post pass before GUP_fast return and after reenabling preempt then >>>> it is fine like it would be for regular GUP. But locking page for GUP >>>> is also likely to slow down some workload (with direct-IO). >>>> >>> >>> Right, and so to crux of the matter: taking an uncontended page lock >>> involves pretty much the same set of operations that your approach does. >>> (If gup ends up contended with the page lock for other reasons than these >>> paths, that seems surprising.) I'd expect very similar performance. >>> >>> But the page lock approach leads to really dramatically simpler code (and >>> code reviews, let's not forget). Any objection to my going that >>> direction, and keeping this idea as a Plan B? I think the next step will >>> be, once again, to gather some performance metrics, so maybe that will >>> help us decide. >> >> FWIW I agree that using page lock for protecting page pinning (and thus >> avoid races with page_mkclean()) looks simpler to me as well and I'm not >> convinced there will be measurable difference to the more complex scheme >> with barriers Jerome suggests unless that page lock contended. Jerome is >> right that you cannot just do lock_page() in gup_fast() path. There you >> have to do trylock_page() and if that fails just bail out to the slow gup >> path. >> Yes, understood about gup fast. >> Regarding places other than page_mkclean() that need to check pinned state: >> Definitely page migration will want to check whether the page is pinned or >> not so that it can deal differently with short-term page references vs >> longer-term pins. OK. >> >> Also there is one more idea I had how to record number of pins in the page: >> >> #define PAGE_PIN_BIAS 1024 >> >> get_page_pin() >> atomic_add(&page->_refcount, PAGE_PIN_BIAS); >> >> put_page_pin(); >> atomic_add(&page->_refcount, -PAGE_PIN_BIAS); >> >> page_pinned(page) >> (atomic_read(&page->_refcount) - page_mapcount(page)) > PAGE_PIN_BIAS >> >> This is pretty trivial scheme. It still gives us 22-bits for page pins >> which should be plenty (but we should check for that and bail with error if >> it would overflow). Also there will be no false negatives and false >> positives only if there are more than 1024 non-page-table references to the >> page which I expect to be rare (we might want to also subtract >> hpage_nr_pages() for radix tree references to avoid excessive false >> positives for huge pages although at this point I don't think they would >> matter). Thoughts? > > Racing PUP are as likely to cause issues: > > CPU0 | CPU1 | CPU2 > | | > | PUP() | > page_pinned(page) | | > (page_count(page) - | | > page_mapcount(page)) | | > | | GUP() > > So here the refcount snap-shot does not include the second GUP and > we can have a false negative ie the page_pinned() will return false > because of the PUP happening just before on CPU1 despite the racing > GUP on CPU2 just after. > > I believe only either lock or memory ordering with barrier can > guarantee that we do not miss GUP ie no false negative. Still the > bias idea might be usefull as with it we should not need a flag. > > So to make the above safe it would still need the page write back > double check that i described so that GUP back-off if it raced with > page_mkclean,clear_page_dirty_for_io and the fs write page call back > which call test_set_page_writeback() (yes it is very unlikely but > might still happen). > > > I still need to ponder some more on all the races. > Tentatively, so far I prefer the _mapcount scheme, because it seems more accurate to add mapcounts than to overload the _refcount field. And the implementation is going to be cleaner. And we've already figured out the races. For example, the following already survives a basic boot to graphics mode. It requires a bunch of callsite conversions, and a page flag (neither of which is shown here), and may also have "a few" gross conceptual errors, but take a peek: >From 1b6e611238a45badda7e63d3ffc089cefb621cb2 Mon Sep 17 00:00:00 2001 From: John Hubbard Date: Sun, 13 Jan 2019 15:10:31 -0800 Subject: [PATCH 2/2] mm: track gup-pinned pages X-NVConfidentiality: public Cc: John Hubbard Track GUP-pinned pages. Signed-off-by: John Hubbard --- include/linux/mm.h | 8 ++++--- mm/gup.c | 59 +++++++++++++++++++++++++++++++++++++++++++--- mm/rmap.c | 23 ++++++++++++++---- 3 files changed, 79 insertions(+), 11 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 809b7397d41e..3221a13b4891 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1004,12 +1004,14 @@ static inline void put_page(struct page *page) * particular, interactions with RDMA and filesystems need special * handling. * - * put_user_page() and put_page() are not interchangeable, despite this early - * implementation that makes them look the same. put_user_page() calls must - * be perfectly matched up with get_user_page() calls. + * put_user_page() and put_page() are not interchangeable. put_user_page() + * calls must be perfectly matched up with get_user_page() calls. */ static inline void put_user_page(struct page *page) { + page = compound_head(page); + + atomic_dec(&page->_mapcount); put_page(page); } diff --git a/mm/gup.c b/mm/gup.c index 05acd7e2eb22..af3909814be7 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -615,6 +615,48 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) return 0; } +/* + * Manages the PG_gup_pinned flag. + * + * Note that page->_mapcount counting part of managing that flag, because the + * _mapcount is used to determine if PG_gup_pinned can be cleared, in + * page_mkclean(). + */ +static void track_gup_page(struct page *page) +{ + page = compound_head(page); + + lock_page(page); + + wait_on_page_writeback(page); + + atomic_inc(&page->_mapcount); + SetPageGupPinned(page); + + unlock_page(page); +} + +/* + * A variant of track_gup_page() that returns -EBUSY, instead of waiting. + */ +static int track_gup_page_atomic(struct page *page) +{ + page = compound_head(page); + + if (PageWriteback(page) || !trylock_page(page)) + return -EBUSY; + + if (PageWriteback(page)) { + unlock_page(page); + return -EBUSY; + } + atomic_inc(&page->_mapcount); + SetPageGupPinned(page); + + unlock_page(page); + return 0; +} + /** * __get_user_pages() - pin user pages in memory * @tsk: task_struct of target task @@ -761,6 +803,9 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, ret = PTR_ERR(page); goto out; } + + track_gup_page(page); + if (pages) { pages[i] = page; flush_anon_page(vma, page, start); @@ -1439,6 +1484,11 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, VM_BUG_ON_PAGE(compound_head(page) != head, page); + if (track_gup_page_atomic(page)) { + put_page(head); + goto pte_unmap; + } + SetPageReferenced(page); pages[*nr] = page; (*nr)++; @@ -1574,7 +1624,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, return 0; } - if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { + if (unlikely(pmd_val(orig) != pmd_val(*pmdp)) || + track_gup_page_atomic(head)) { *nr -= refs; while (refs--) put_page(head); @@ -1612,7 +1663,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, return 0; } - if (unlikely(pud_val(orig) != pud_val(*pudp))) { + if (unlikely(pud_val(orig) != pud_val(*pudp)) || + track_gup_page_atomic(head)) { *nr -= refs; while (refs--) put_page(head); @@ -1649,7 +1701,8 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, return 0; } - if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) { + if (unlikely(pgd_val(orig) != pgd_val(*pgdp)) || + track_gup_page_atomic(head)) { *nr -= refs; while (refs--) put_page(head); diff --git a/mm/rmap.c b/mm/rmap.c index 0454ecc29537..434283898bb0 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -880,6 +880,11 @@ int page_referenced(struct page *page, return pra.referenced; } +struct page_mkclean_args { + int cleaned; + int mapcount; +}; + static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, unsigned long address, void *arg) { @@ -890,7 +895,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, .flags = PVMW_SYNC, }; struct mmu_notifier_range range; - int *cleaned = arg; + struct page_mkclean_args *pma = arg; /* * We have to assume the worse case ie pmd for invalidation. Note that @@ -940,6 +945,8 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, #endif } + pma->mapcount++; + /* * No need to call mmu_notifier_invalidate_range() as we are * downgrading page table protection not changing it to point @@ -948,7 +955,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, * See Documentation/vm/mmu_notifier.rst */ if (ret) - (*cleaned)++; + pma->cleaned++; } mmu_notifier_invalidate_range_end(&range); @@ -966,10 +973,13 @@ static bool invalid_mkclean_vma(struct vm_area_struct *vma, void *arg) int page_mkclean(struct page *page) { - int cleaned = 0; + struct page_mkclean_args pma = { + .cleaned = 0, + .mapcount = 0 + }; struct address_space *mapping; struct rmap_walk_control rwc = { - .arg = (void *)&cleaned, + .arg = (void *)&pma, .rmap_one = page_mkclean_one, .invalid_vma = invalid_mkclean_vma, }; @@ -985,7 +995,10 @@ int page_mkclean(struct page *page) rmap_walk(page, &rwc); - return cleaned; + if (pma.mapcount == page_mapcount(page)) + ClearPageGupPinned(page); + + return pma.cleaned; } EXPORT_SYMBOL_GPL(page_mkclean); -- 2.20.1 thanks, -- John Hubbard NVIDIA