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From: Mike Rapoport <rppt@linux.ibm.com>
To: john.hubbard@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, Al Viro <viro@zeniv.linux.org.uk>,
	Christian Benvenuti <benve@cisco.com>,
	Christoph Hellwig <hch@infradead.org>,
	Christopher Lameter <cl@linux.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Chinner <david@fromorbit.com>,
	Dennis Dalessandro <dennis.dalessandro@intel.com>,
	Doug Ledford <dledford@redhat.com>, Jan Kara <jack@suse.cz>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Jerome Glisse <jglisse@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@kernel.org>,
	Mike Marciniszyn <mike.marciniszyn@intel.com>,
	Ralph Campbell <rcampbell@nvidia.com>,
	Tom Talpey <tom@talpey.com>, LKML <linux-kernel@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org, John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions
Date: Fri, 8 Feb 2019 12:32:12 +0200
Message-ID: <20190208103211.GD11096@rapoport-lnx> (raw)
In-Reply-To: <20190208075649.3025-2-jhubbard@nvidia.com>

On Thu, Feb 07, 2019 at 11:56:48PM -0800, john.hubbard@gmail.com wrote:
> From: John Hubbard <jhubbard@nvidia.com>
> 
> Introduces put_user_page(), which simply calls put_page().
> This provides a way to update all get_user_pages*() callers,
> so that they call put_user_page(), instead of put_page().
> 
> Also introduces put_user_pages(), and a few dirty/locked variations,
> as a replacement for release_pages(), and also as a replacement
> for open-coded loops that release multiple pages.
> These may be used for subsequent performance improvements,
> via batching of pages to be released.
> 
> This is the first step of fixing a problem (also described in [1] and
> [2]) with interactions between get_user_pages ("gup") and filesystems.
> 
> Problem description: let's start with a bug report. Below, is what happens
> sometimes, under memory pressure, when a driver pins some pages via gup,
> and then marks those pages dirty, and releases them. Note that the gup
> documentation actually recommends that pattern. The problem is that the
> filesystem may do a writeback while the pages were gup-pinned, and then the
> filesystem believes that the pages are clean. So, when the driver later
> marks the pages as dirty, that conflicts with the filesystem's page
> tracking and results in a BUG(), like this one that I experienced:
> 
>     kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899!
>     backtrace:
>         ext4_writepage
>         __writepage
>         write_cache_pages
>         ext4_writepages
>         do_writepages
>         __writeback_single_inode
>         writeback_sb_inodes
>         __writeback_inodes_wb
>         wb_writeback
>         wb_workfn
>         process_one_work
>         worker_thread
>         kthread
>         ret_from_fork
> 
> ...which is due to the file system asserting that there are still buffer
> heads attached:
> 
>         ({                                                      \
>                 BUG_ON(!PagePrivate(page));                     \
>                 ((struct buffer_head *)page_private(page));     \
>         })
> 
> Dave Chinner's description of this is very clear:
> 
>     "The fundamental issue is that ->page_mkwrite must be called on every
>     write access to a clean file backed page, not just the first one.
>     How long the GUP reference lasts is irrelevant, if the page is clean
>     and you need to dirty it, you must call ->page_mkwrite before it is
>     marked writeable and dirtied. Every. Time."
> 
> This is just one symptom of the larger design problem: filesystems do not
> actually support get_user_pages() being called on their pages, and letting
> hardware write directly to those pages--even though that patter has been
> going on since about 2005 or so.
> 
> The steps are to fix it are:
> 
> 1) (This patch): provide put_user_page*() routines, intended to be used
>    for releasing pages that were pinned via get_user_pages*().
> 
> 2) Convert all of the call sites for get_user_pages*(), to
>    invoke put_user_page*(), instead of put_page(). This involves dozens of
>    call sites, and will take some time.
> 
> 3) After (2) is complete, use get_user_pages*() and put_user_page*() to
>    implement tracking of these pages. This tracking will be separate from
>    the existing struct page refcounting.
> 
> 4) Use the tracking and identification of these pages, to implement
>    special handling (especially in writeback paths) when the pages are
>    backed by a filesystem.
> 
> [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()"
> [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()"
> 
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Christopher Lameter <cl@linux.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Jerome Glisse <jglisse@redhat.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: Ralph Campbell <rcampbell@nvidia.com>
> 
> Reviewed-by: Jan Kara <jack@suse.cz>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  include/linux/mm.h | 24 ++++++++++++++
>  mm/swap.c          | 82 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 106 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 80bb6408fe73..809b7397d41e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -993,6 +993,30 @@ static inline void put_page(struct page *page)
>  		__put_page(page);
>  }
>  
> +/**
> + * put_user_page() - release a gup-pinned page
> + * @page:            pointer to page to be released
> + *
> + * Pages that were pinned via get_user_pages*() must be released via
> + * either put_user_page(), or one of the put_user_pages*() routines
> + * below. This is so that eventually, pages that are pinned via
> + * get_user_pages*() can be separately tracked and uniquely handled. In
> + * 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

I just hope we'll remember to update when the real implementation will be
merged ;-)

Other than that, feel free to add

Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>	# docs 

> + * be perfectly matched up with get_user_page() calls.
> + */
> +static inline void put_user_page(struct page *page)
> +{
> +	put_page(page);
> +}
> +
> +void put_user_pages_dirty(struct page **pages, unsigned long npages);
> +void put_user_pages_dirty_lock(struct page **pages, unsigned long npages);
> +void put_user_pages(struct page **pages, unsigned long npages);
> +
>  #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
>  #define SECTION_IN_PAGE_FLAGS
>  #endif
> diff --git a/mm/swap.c b/mm/swap.c
> index 4929bc1be60e..7c42ca45bb89 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -133,6 +133,88 @@ void put_pages_list(struct list_head *pages)
>  }
>  EXPORT_SYMBOL(put_pages_list);
>  
> +typedef int (*set_dirty_func)(struct page *page);
> +
> +static void __put_user_pages_dirty(struct page **pages,
> +				   unsigned long npages,
> +				   set_dirty_func sdf)
> +{
> +	unsigned long index;
> +
> +	for (index = 0; index < npages; index++) {
> +		struct page *page = compound_head(pages[index]);
> +
> +		if (!PageDirty(page))
> +			sdf(page);
> +
> +		put_user_page(page);
> +	}
> +}
> +
> +/**
> + * put_user_pages_dirty() - release and dirty an array of gup-pinned pages
> + * @pages:  array of pages to be marked dirty and released.
> + * @npages: number of pages in the @pages array.
> + *
> + * "gup-pinned page" refers to a page that has had one of the get_user_pages()
> + * variants called on that page.
> + *
> + * For each page in the @pages array, make that page (or its head page, if a
> + * compound page) dirty, if it was previously listed as clean. Then, release
> + * the page using put_user_page().
> + *
> + * Please see the put_user_page() documentation for details.
> + *
> + * set_page_dirty(), which does not lock the page, is used here.
> + * Therefore, it is the caller's responsibility to ensure that this is
> + * safe. If not, then put_user_pages_dirty_lock() should be called instead.
> + *
> + */
> +void put_user_pages_dirty(struct page **pages, unsigned long npages)
> +{
> +	__put_user_pages_dirty(pages, npages, set_page_dirty);
> +}
> +EXPORT_SYMBOL(put_user_pages_dirty);
> +
> +/**
> + * put_user_pages_dirty_lock() - release and dirty an array of gup-pinned pages
> + * @pages:  array of pages to be marked dirty and released.
> + * @npages: number of pages in the @pages array.
> + *
> + * For each page in the @pages array, make that page (or its head page, if a
> + * compound page) dirty, if it was previously listed as clean. Then, release
> + * the page using put_user_page().
> + *
> + * Please see the put_user_page() documentation for details.
> + *
> + * This is just like put_user_pages_dirty(), except that it invokes
> + * set_page_dirty_lock(), instead of set_page_dirty().
> + *
> + */
> +void put_user_pages_dirty_lock(struct page **pages, unsigned long npages)
> +{
> +	__put_user_pages_dirty(pages, npages, set_page_dirty_lock);
> +}
> +EXPORT_SYMBOL(put_user_pages_dirty_lock);
> +
> +/**
> + * put_user_pages() - release an array of gup-pinned pages.
> + * @pages:  array of pages to be marked dirty and released.
> + * @npages: number of pages in the @pages array.
> + *
> + * For each page in the @pages array, release the page using put_user_page().
> + *
> + * Please see the put_user_page() documentation for details.
> + */
> +void put_user_pages(struct page **pages, unsigned long npages)
> +{
> +	unsigned long index;
> +
> +	for (index = 0; index < npages; index++)
> +		put_user_page(pages[index]);
> +}
> +EXPORT_SYMBOL(put_user_pages);
> +
>  /*
>   * get_kernel_pages() - pin kernel pages in memory
>   * @kiov:	An array of struct kvec structures
> -- 
> 2.20.1
> 

-- 
Sincerely yours,
Mike.


  reply index

Thread overview: 177+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-08  7:56 [PATCH 0/2] mm: put_user_page() call site conversion first john.hubbard
2019-02-08  7:56 ` [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions john.hubbard
2019-02-08 10:32   ` Mike Rapoport [this message]
2019-02-08 20:44     ` John Hubbard
2019-02-08  7:56 ` [PATCH 2/2] infiniband/mm: convert put_page() to put_user_page*() john.hubbard
2019-02-15  0:23 ` [PATCH 0/2] mm: put_user_page() call site conversion first Ira Weiny
2019-02-15  0:54   ` John Hubbard
  -- strict thread matches above, loose matches on Subject: below --
2018-12-04  0:17 [PATCH 0/2] put_user_page*(): start converting the call sites john.hubbard
2018-12-04  0:17 ` [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions john.hubbard
2018-12-04  7:53   ` Mike Rapoport
2018-12-05  1:40     ` John Hubbard
2018-12-04 20:28   ` Dan Williams
2018-12-04 21:56     ` John Hubbard
2018-12-04 23:03       ` Dan Williams
2018-12-05  0:36         ` Jerome Glisse
2018-12-05  0:40           ` Dan Williams
2018-12-05  0:59             ` John Hubbard
2018-12-05  0:58         ` John Hubbard
2018-12-05  1:00           ` Dan Williams
2018-12-05  1:15           ` Matthew Wilcox
2018-12-05  1:44             ` Jerome Glisse
2018-12-05  1:57               ` John Hubbard
2018-12-07  2:45                 ` John Hubbard
2018-12-07 19:16                   ` Jerome Glisse
2018-12-07 19:26                     ` Dan Williams
2018-12-07 19:40                       ` Jerome Glisse
2018-12-08  0:52                     ` John Hubbard
2018-12-08  2:24                       ` Jerome Glisse
2018-12-10 10:28                         ` Jan Kara
2018-12-12 15:03                           ` Jerome Glisse
2018-12-12 16:27                             ` Dan Williams
2018-12-12 17:02                               ` Jerome Glisse
2018-12-12 17:49                                 ` Dan Williams
2018-12-12 19:07                                   ` John Hubbard
2018-12-12 21:30                               ` Jerome Glisse
2018-12-12 21:40                                 ` Dan Williams
2018-12-12 21:53                                   ` Jerome Glisse
2018-12-12 22:11                                     ` Matthew Wilcox
2018-12-12 22:16                                       ` Jerome Glisse
2018-12-12 23:37                                     ` Jason Gunthorpe
2018-12-12 23:46                                       ` John Hubbard
2018-12-12 23:54                                       ` Dan Williams
2018-12-13  0:01                                       ` Jerome Glisse
2018-12-13  0:18                                         ` Dan Williams
2018-12-13  0:44                                           ` Jerome Glisse
2018-12-13  3:26                                             ` Jason Gunthorpe
2018-12-13  3:20                                         ` Jason Gunthorpe
2018-12-13 12:43                                           ` Jerome Glisse
2018-12-13 13:40                                             ` Tom Talpey
2018-12-13 14:18                                               ` Jerome Glisse
2018-12-13 14:51                                                 ` Tom Talpey
2018-12-13 15:18                                                   ` Jerome Glisse
2018-12-13 18:12                                                     ` Tom Talpey
2018-12-13 19:18                                                       ` Jerome Glisse
2018-12-14 10:41                                             ` Jan Kara
2018-12-14 15:25                                               ` Jerome Glisse
2018-12-12 21:56                                 ` John Hubbard
2018-12-12 22:04                                   ` Jerome Glisse
2018-12-12 22:11                                     ` John Hubbard
2018-12-12 22:14                                       ` Jerome Glisse
2018-12-12 22:17                                         ` John Hubbard
2018-12-12 21:46                             ` Dave Chinner
2018-12-12 21:59                               ` Jerome Glisse
2018-12-13  0:51                                 ` Dave Chinner
2018-12-13  2:02                                   ` Jerome Glisse
2018-12-13 15:56                                     ` Christopher Lameter
2018-12-13 16:02                                       ` Jerome Glisse
2018-12-14  6:00                                     ` Dave Chinner
2018-12-14 15:13                                       ` Jerome Glisse
2018-12-14  3:52                                   ` John Hubbard
2018-12-14  5:21                                     ` Dan Williams
2018-12-14  6:11                                       ` John Hubbard
2018-12-14 15:20                                         ` Jerome Glisse
2018-12-14 19:38                                         ` Dan Williams
2018-12-14 19:48                                           ` Matthew Wilcox
2018-12-14 19:53                                             ` Dave Hansen
2018-12-14 20:03                                               ` Matthew Wilcox
2018-12-14 20:17                                                 ` Dan Williams
2018-12-14 20:29                                                   ` Matthew Wilcox
2018-12-15  0:41                                                 ` John Hubbard
2018-12-17  8:56                                           ` Jan Kara
2018-12-17 18:28                                             ` Dan Williams
2018-12-14 15:43                               ` Jan Kara
2018-12-16 21:58                                 ` Dave Chinner
2018-12-17 18:11                                   ` Jerome Glisse
2018-12-17 18:34                                     ` Matthew Wilcox
2018-12-17 19:48                                       ` Jerome Glisse
2018-12-17 19:51                                         ` Matthew Wilcox
2018-12-17 19:54                                           ` Jerome Glisse
2018-12-17 19:59                                             ` Matthew Wilcox
2018-12-17 20:55                                               ` Jerome Glisse
2018-12-17 21:03                                                 ` Matthew Wilcox
2018-12-17 21:15                                                   ` Jerome Glisse
2018-12-18  1:09                                       ` Dave Chinner
2018-12-18  6:12                                       ` Darrick J. Wong
2018-12-18  9:30                                       ` Jan Kara
2018-12-18 23:29                                         ` John Hubbard
2018-12-19  2:07                                           ` Jerome Glisse
2018-12-19 11:08                                             ` Jan Kara
2018-12-20 10:54                                               ` John Hubbard
2018-12-20 16:50                                                 ` Jerome Glisse
2018-12-20 16:57                                                   ` Dan Williams
2018-12-20 16:49                                               ` Jerome Glisse
2019-01-03  1:55                                               ` Jerome Glisse
2019-01-03  3:27                                                 ` John Hubbard
2019-01-03 14:57                                                   ` Jerome Glisse
2019-01-03  9:26                                                 ` Jan Kara
2019-01-03 14:44                                                   ` Jerome Glisse
2019-01-11  2:59                                                     ` John Hubbard
2019-01-11 16:51                                                       ` Jerome Glisse
2019-01-12  1:04                                                         ` John Hubbard
2019-01-12  2:02                                                           ` Jerome Glisse
2019-01-12  2:38                                                             ` John Hubbard
2019-01-12  2:46                                                               ` Jerome Glisse
2019-01-12  3:06                                                                 ` John Hubbard
2019-01-12  3:25                                                                   ` Jerome Glisse
2019-01-12 20:46                                                                     ` John Hubbard
2019-01-14 14:54                                                                   ` Jan Kara
2019-01-14 17:21                                                                     ` Jerome Glisse
2019-01-14 19:09                                                                       ` John Hubbard
2019-01-15  8:34                                                                         ` Jan Kara
2019-01-15 21:39                                                                           ` John Hubbard
2019-01-15  8:07                                                                       ` Jan Kara
2019-01-15 17:15                                                                         ` Jerome Glisse
2019-01-15 21:56                                                                           ` John Hubbard
2019-01-15 22:12                                                                             ` Jerome Glisse
2019-01-16  0:44                                                                               ` John Hubbard
2019-01-16  1:56                                                                                 ` Jerome Glisse
2019-01-16  2:01                                                                                   ` Dan Williams
2019-01-16  2:23                                                                                     ` Jerome Glisse
2019-01-16  4:34                                                                                       ` Dave Chinner
2019-01-16 14:50                                                                                         ` Jerome Glisse
2019-01-16 22:51                                                                                           ` Dave Chinner
2019-01-16 11:38                                                                         ` Jan Kara
2019-01-16 13:08                                                                           ` Jerome Glisse
2019-01-17  5:42                                                                             ` John Hubbard
2019-01-17 15:21                                                                               ` Jerome Glisse
2019-01-18  0:16                                                                                 ` Dave Chinner
2019-01-18  1:59                                                                                   ` Jerome Glisse
2019-01-17  9:30                                                                             ` Jan Kara
2019-01-17 15:17                                                                               ` Jerome Glisse
2019-01-22 15:24                                                                                 ` Jan Kara
2019-01-22 16:46                                                                                   ` Jerome Glisse
2019-01-23 18:02                                                                                     ` Jan Kara
2019-01-23 19:04                                                                                       ` Jerome Glisse
2019-01-29  0:22                                                                                         ` John Hubbard
2019-01-29  1:23                                                                                           ` Jerome Glisse
2019-01-29  6:41                                                                                             ` John Hubbard
2019-01-29 10:12                                                                                               ` Jan Kara
2019-01-30  2:21                                                                                                 ` John Hubbard
2019-01-17  5:25                                                                         ` John Hubbard
2019-01-17  9:04                                                                           ` Jan Kara
2019-01-12  3:14                                                               ` Jerome Glisse
2018-12-18 10:33                                   ` Jan Kara
2018-12-18 23:42                                     ` Dave Chinner
2018-12-19  3:03                                       ` Jason Gunthorpe
2018-12-19  5:26                                         ` Dan Williams
2018-12-19 11:19                                           ` Jan Kara
2018-12-19 10:28                                         ` Dave Chinner
2018-12-19 11:35                                           ` Jan Kara
2018-12-19 16:56                                             ` Jason Gunthorpe
2018-12-19 22:33                                             ` Dave Chinner
2018-12-20  9:07                                               ` Jan Kara
2018-12-20 16:54                                               ` Jerome Glisse
2018-12-19 13:24                                       ` Jan Kara
2018-12-08  5:18                       ` Matthew Wilcox
2018-12-12 19:13                         ` John Hubbard
2018-12-08  7:16                       ` Dan Williams
2018-12-08 16:33                         ` Jerome Glisse
2018-12-08 16:48                           ` Christoph Hellwig
2018-12-08 17:47                             ` Jerome Glisse
2018-12-08 18:26                               ` Christoph Hellwig
2018-12-08 18:45                                 ` Jerome Glisse
2018-12-08 18:09                             ` Dan Williams
2018-12-08 18:12                               ` Christoph Hellwig
2018-12-11  6:18                               ` Dave Chinner
2018-12-05  5:52             ` Dan Williams
2018-12-05 11:16       ` Jan Kara

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