From patchwork Sat Mar 10 06:55:37 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dan Williams X-Patchwork-Id: 10273239 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 5F073605D2 for ; Sat, 10 Mar 2018 07:04:57 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4EC6828909 for ; Sat, 10 Mar 2018 07:04:57 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 41FB029F19; Sat, 10 Mar 2018 07:04:57 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.9 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_NONE autolearn=unavailable version=3.3.1 Received: from ml01.01.org (ml01.01.org [198.145.21.10]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 4D2DA28909 for ; Sat, 10 Mar 2018 07:04:44 +0000 (UTC) Received: from [127.0.0.1] (localhost [IPv6:::1]) by ml01.01.org (Postfix) with ESMTP id DF962220C2A5E; Fri, 9 Mar 2018 22:58:25 -0800 (PST) X-Original-To: linux-nvdimm@lists.01.org Delivered-To: linux-nvdimm@lists.01.org Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=134.134.136.65; helo=mga03.intel.com; envelope-from=dan.j.williams@intel.com; receiver=linux-nvdimm@lists.01.org Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id A90CF220C2A58 for ; Fri, 9 Mar 2018 22:58:24 -0800 (PST) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 09 Mar 2018 23:04:42 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.47,449,1515484800"; d="scan'208";a="33872581" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.16]) by orsmga003.jf.intel.com with ESMTP; 09 Mar 2018 23:04:42 -0800 Subject: [PATCH v5 09/11] mm, fs, dax: handle layout changes to pinned dax mappings From: Dan Williams To: linux-nvdimm@lists.01.org Date: Fri, 09 Mar 2018 22:55:37 -0800 Message-ID: <152066493762.40260.14701327157254972582.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <152066488891.40260.14605734226832760468.stgit@dwillia2-desk3.amr.corp.intel.com> References: <152066488891.40260.14605734226832760468.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.18-2-gc94f MIME-Version: 1.0 X-BeenThere: linux-nvdimm@lists.01.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "Linux-nvdimm developer list." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dave Hansen , jack@suse.cz, "Darrick J. Wong" , Matthew Wilcox , Dave Chinner , linux-kernel@vger.kernel.org, hch@lst.de, linux-xfs@vger.kernel.org, Alexander Viro , linux-fsdevel@vger.kernel.org, Andrew Morton Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" X-Virus-Scanned: ClamAV using ClamSMTP Background: get_user_pages() in the filesystem pins file backed memory pages for access by devices performing dma. However, it only pins the memory pages not the page-to-file offset association. If a file is truncated the pages are mapped out of the file and dma may continue indefinitely into a page that is owned by a device driver. This breaks coherency of the file vs dma, but the assumption is that if userspace wants the file-space truncated it does not matter what data is inbound from the device, it is not relevant anymore. The only expectation is that dma can safely continue while the filesystem reallocates the block(s). Problem: This expectation that dma can safely continue while the filesystem changes the block map is broken by dax. With dax the target dma page *is* the filesystem block. The model of leaving the page pinned for dma, but truncating the file block out of the file, means that the filesytem is free to reallocate a block under active dma to another file and now the expected data-incoherency situation has turned into active data-corruption. Solution: Defer all filesystem operations (fallocate(), truncate()) on a dax mode file while any page/block in the file is under active dma. This solution assumes that dma is transient. Cases where dma operations are known to not be transient, like RDMA, have been explicitly disabled via commits like 5f1d43de5416 "IB/core: disable memory registration of filesystem-dax vmas". The dax_layout_busy_page() routine is called by filesystems with a lock held against mm faults (i_mmap_lock) to find pinned / busy dax pages. The process of looking up a busy page invalidates all mappings to trigger any subsequent get_user_pages() to block on i_mmap_lock. The filesystem continues to call dax_layout_busy_page() until it finally returns no more active pages. This approach assumes that the page pinning is transient, if that assumption is violated the system would have likely hung from the uncompleted I/O. Cc: Jan Kara Cc: Jeff Moyer Cc: Dave Chinner Cc: Matthew Wilcox Cc: Alexander Viro Cc: "Darrick J. Wong" Cc: Ross Zwisler Cc: Dave Hansen Cc: Andrew Morton Reported-by: Christoph Hellwig Signed-off-by: Dan Williams --- fs/dax.c | 93 +++++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/dax.h | 30 ++++++++++++++++ mm/gup.c | 5 +++ 3 files changed, 128 insertions(+) diff --git a/fs/dax.c b/fs/dax.c index fecf463a1468..cfaaf31fae85 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -375,6 +375,19 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping, } } +static struct page *dax_busy_page(void *entry) +{ + unsigned long pfn, end_pfn; + + for_each_entry_pfn(entry, pfn, end_pfn) { + struct page *page = pfn_to_page(pfn); + + if (page_ref_count(page) > 1) + return page; + } + return NULL; +} + /* * Find radix tree entry at given index. If it points to an exceptional entry, * return it with the radix tree entry locked. If the radix tree doesn't @@ -516,6 +529,85 @@ static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index, return entry; } +/** + * dax_layout_busy_page - find first pinned page in @mapping + * @mapping: address space to scan for a page with ref count > 1 + * + * DAX requires ZONE_DEVICE mapped pages. These pages are never + * 'onlined' to the page allocator so they are considered idle when + * page->count == 1. A filesystem uses this interface to determine if + * any page in the mapping is busy, i.e. for DMA, or other + * get_user_pages() usages. + * + * It is expected that the filesystem is holding locks to block the + * establishment of new mappings in this address_space. I.e. it expects + * to be able to run unmap_mapping_range() and subsequently not race + * mapping_mapped() becoming true. It expects that get_user_pages() pte + * walks are performed under rcu_read_lock(). + */ +struct page *dax_layout_busy_page(struct address_space *mapping) +{ + pgoff_t indices[PAGEVEC_SIZE]; + struct page *page = NULL; + struct pagevec pvec; + pgoff_t index, end; + unsigned i; + + /* + * In the 'limited' case get_user_pages() for dax is disabled. + */ + if (IS_ENABLED(CONFIG_FS_DAX_LIMITED)) + return NULL; + + if (!dax_mapping(mapping) || !mapping_mapped(mapping)) + return NULL; + + pagevec_init(&pvec); + index = 0; + end = -1; + /* + * Flush dax_layout_lock() sections to ensure all possible page + * references have been taken, or otherwise arrange for faults + * to block on the filesystem lock that is taken for + * establishing new mappings. + */ + unmap_mapping_range(mapping, 0, 0, 1); + synchronize_rcu(); + + while (index < end && pagevec_lookup_entries(&pvec, mapping, index, + min(end - index, (pgoff_t)PAGEVEC_SIZE), + indices)) { + for (i = 0; i < pagevec_count(&pvec); i++) { + struct page *pvec_ent = pvec.pages[i]; + void *entry; + + index = indices[i]; + if (index >= end) + break; + + if (!radix_tree_exceptional_entry(pvec_ent)) + continue; + + spin_lock_irq(&mapping->tree_lock); + entry = get_unlocked_mapping_entry(mapping, index, NULL); + if (entry) + page = dax_busy_page(entry); + put_unlocked_mapping_entry(mapping, index, entry); + spin_unlock_irq(&mapping->tree_lock); + if (page) + break; + } + pagevec_remove_exceptionals(&pvec); + pagevec_release(&pvec); + index++; + + if (page) + break; + } + return page; +} +EXPORT_SYMBOL_GPL(dax_layout_busy_page); + static int __dax_invalidate_mapping_entry(struct address_space *mapping, pgoff_t index, bool trunc) { @@ -540,6 +632,7 @@ static int __dax_invalidate_mapping_entry(struct address_space *mapping, spin_unlock_irq(&mapping->tree_lock); return ret; } + /* * Delete exceptional DAX entry at @index from @mapping. Wait for radix tree * entry to get unlocked before deleting it. diff --git a/include/linux/dax.h b/include/linux/dax.h index 9b4259aee016..62671a636512 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -56,6 +56,18 @@ void fs_dax_release(struct dax_device *dax_dev, void *owner); int dax_set_page_dirty(struct page *page); void dax_invalidatepage(struct page *page, unsigned int offset, unsigned int length); + +static inline void dax_layout_lock(void) +{ + rcu_read_lock(); +} + +static inline void dax_layout_unlock(void) +{ + rcu_read_unlock(); +} + +struct page *dax_layout_busy_page(struct address_space *mapping); #else static inline int bdev_dax_supported(struct super_block *sb, int blocksize) { @@ -79,6 +91,19 @@ static inline void fs_dax_release(struct dax_device *dax_dev, void *owner) #define dax_set_page_dirty NULL #define dax_invalidatepage NULL + +static inline void dax_layout_lock(void) +{ +} + +static inline void dax_layout_unlock(void) +{ +} + +static inline struct page *dax_layout_busy_page(struct address_space *mapping) +{ + return NULL; +} #endif int dax_read_lock(void); @@ -108,6 +133,11 @@ int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index); int dax_invalidate_mapping_entry_sync(struct address_space *mapping, pgoff_t index); +static inline struct page *refcount_to_page(atomic_t *c) +{ + return container_of(c, struct page, _refcount); +} + #ifdef CONFIG_FS_DAX int __dax_zero_page_range(struct block_device *bdev, struct dax_device *dax_dev, sector_t sector, diff --git a/mm/gup.c b/mm/gup.c index 1b46e6e74881..a81efac6983a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -13,6 +13,7 @@ #include #include #include +#include #include #include @@ -693,7 +694,9 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, if (unlikely(fatal_signal_pending(current))) return i ? i : -ERESTARTSYS; cond_resched(); + dax_layout_lock(); page = follow_page_mask(vma, start, foll_flags, &page_mask); + dax_layout_unlock(); if (!page) { int ret; ret = faultin_page(tsk, vma, start, &foll_flags, @@ -1809,7 +1812,9 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, if (gup_fast_permitted(start, nr_pages, write)) { local_irq_disable(); + dax_layout_lock(); gup_pgd_range(addr, end, write, pages, &nr); + dax_layout_unlock(); local_irq_enable(); ret = nr; }