From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga09.intel.com ([134.134.136.24]:18976 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754225AbeCUXGz (ORCPT ); Wed, 21 Mar 2018 19:06:55 -0400 Subject: [PATCH v7 07/14] fs, dax: use page->mapping to warn if truncate collides with a busy page From: Dan Williams To: linux-nvdimm@lists.01.org Cc: Jeff Moyer , Matthew Wilcox , Ross Zwisler , Jan Kara , Christoph Hellwig , david@fromorbit.com, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, jack@suse.cz Date: Wed, 21 Mar 2018 15:57:48 -0700 Message-ID: <152167306807.5268.8483232024444414342.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <152167302988.5268.4370226749268662682.stgit@dwillia2-desk3.amr.corp.intel.com> References: <152167302988.5268.4370226749268662682.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Catch cases where extent unmap operations encounter pages that are pinned / busy. Typically this is pinned pages that are under active dma. This warning is a canary for potential data corruption as truncated blocks could be allocated to a new file while the device is still performing i/o. Here is an example of a collision that this implementation catches: WARNING: CPU: 2 PID: 1286 at fs/dax.c:343 dax_disassociate_entry+0x55/0x80 [..] Call Trace: __dax_invalidate_mapping_entry+0x6c/0xf0 dax_delete_mapping_entry+0xf/0x20 truncate_exceptional_pvec_entries.part.12+0x1af/0x200 truncate_inode_pages_range+0x268/0x970 ? tlb_gather_mmu+0x10/0x20 ? up_write+0x1c/0x40 ? unmap_mapping_range+0x73/0x140 xfs_free_file_space+0x1b6/0x5b0 [xfs] ? xfs_file_fallocate+0x7f/0x320 [xfs] ? down_write_nested+0x40/0x70 ? xfs_ilock+0x21d/0x2f0 [xfs] xfs_file_fallocate+0x162/0x320 [xfs] ? rcu_read_lock_sched_held+0x3f/0x70 ? rcu_sync_lockdep_assert+0x2a/0x50 ? __sb_start_write+0xd0/0x1b0 ? vfs_fallocate+0x20c/0x270 vfs_fallocate+0x154/0x270 SyS_fallocate+0x43/0x80 entry_SYSCALL_64_fastpath+0x1f/0x96 Cc: Jeff Moyer Cc: Matthew Wilcox Cc: Ross Zwisler Reviewed-by: Jan Kara Reviewed-by: Christoph Hellwig Signed-off-by: Dan Williams --- fs/dax.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) diff --git a/fs/dax.c b/fs/dax.c index b646a46e4d12..f21a8e7e47f6 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -298,6 +298,56 @@ static void put_unlocked_mapping_entry(struct address_space *mapping, dax_wake_mapping_entry_waiter(mapping, index, entry, false); } +static unsigned long dax_entry_size(void *entry) +{ + if (dax_is_zero_entry(entry)) + return 0; + else if (dax_is_empty_entry(entry)) + return 0; + else if (dax_is_pmd_entry(entry)) + return PMD_SIZE; + else + return PAGE_SIZE; +} + +#define for_each_entry_pfn(entry, pfn, end_pfn) \ + for (pfn = dax_radix_pfn(entry), \ + end_pfn = pfn + dax_entry_size(entry) / PAGE_SIZE; \ + pfn < end_pfn; \ + pfn++) + +static void dax_associate_entry(void *entry, struct address_space *mapping) +{ + unsigned long pfn, end_pfn; + + if (IS_ENABLED(CONFIG_FS_DAX_LIMITED)) + return; + + for_each_entry_pfn(entry, pfn, end_pfn) { + struct page *page = pfn_to_page(pfn); + + WARN_ON_ONCE(page->mapping); + page->mapping = mapping; + } +} + +static void dax_disassociate_entry(void *entry, struct address_space *mapping, + bool trunc) +{ + unsigned long pfn, end_pfn; + + if (IS_ENABLED(CONFIG_FS_DAX_LIMITED)) + return; + + for_each_entry_pfn(entry, pfn, end_pfn) { + struct page *page = pfn_to_page(pfn); + + WARN_ON_ONCE(trunc && page_ref_count(page) > 1); + WARN_ON_ONCE(page->mapping && page->mapping != mapping); + page->mapping = 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 @@ -404,6 +454,7 @@ static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index, } if (pmd_downgrade) { + dax_disassociate_entry(entry, mapping, false); radix_tree_delete(&mapping->page_tree, index); mapping->nrexceptional--; dax_wake_mapping_entry_waiter(mapping, index, entry, @@ -453,6 +504,7 @@ static int __dax_invalidate_mapping_entry(struct address_space *mapping, (radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_DIRTY) || radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))) goto out; + dax_disassociate_entry(entry, mapping, trunc); radix_tree_delete(page_tree, index); mapping->nrexceptional--; ret = 1; @@ -547,6 +599,10 @@ static void *dax_insert_mapping_entry(struct address_space *mapping, spin_lock_irq(&mapping->tree_lock); new_entry = dax_radix_locked_entry(pfn, flags); + if (dax_entry_size(entry) != dax_entry_size(new_entry)) { + dax_disassociate_entry(entry, mapping, false); + dax_associate_entry(new_entry, mapping); + } if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) { /*