From: Jan Kara Subject: [PATCH 13/18] dax: Make huge page handling depend of CONFIG_BROKEN Date: Mon, 18 Apr 2016 23:35:36 +0200 Message-ID: <1461015341-20153-14-git-send-email-jack@suse.cz> References: <1461015341-20153-1-git-send-email-jack@suse.cz> Cc: linux-ext4@vger.kernel.org, linux-mm@kvack.org, Ross Zwisler , Dan Williams , linux-nvdimm@lists.01.org, Matthew Wilcox , Jan Kara To: linux-fsdevel@vger.kernel.org Return-path: Received: from mx2.suse.de ([195.135.220.15]:33776 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751430AbcDRVfz (ORCPT ); Mon, 18 Apr 2016 17:35:55 -0400 In-Reply-To: <1461015341-20153-1-git-send-email-jack@suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: Currently the handling of huge pages for DAX is racy. For example the following can happen: CPU0 (THP write fault) CPU1 (normal read fault) __dax_pmd_fault() __dax_fault() get_block(inode, block, &bh, 0) -> not mapped get_block(inode, block, &bh, 0) -> not mapped if (!buffer_mapped(&bh) && write) get_block(inode, block, &bh, 1) -> allocates blocks truncate_pagecache_range(inode, lstart, lend); dax_load_hole(); This results in data corruption since process on CPU1 won't see changes into the file done by CPU0. The race can happen even if two normal faults race however with THP the situation is even worse because the two faults don't operate on the same entries in the radix tree and we want to use these entries for serialization. So make THP support in DAX code depend on CONFIG_BROKEN for now. Signed-off-by: Jan Kara --- fs/dax.c | 2 +- include/linux/dax.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index d7addfab2094..388327f56fa8 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -707,7 +707,7 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf, } EXPORT_SYMBOL_GPL(dax_fault); -#ifdef CONFIG_TRANSPARENT_HUGEPAGE +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_BROKEN) /* * The 'colour' (ie low bits) within a PMD of a page offset. This comes up * more often than one might expect in the below function. diff --git a/include/linux/dax.h b/include/linux/dax.h index 7c45ac7ea1d1..0591f4853228 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -23,7 +23,7 @@ static inline struct page *read_dax_sector(struct block_device *bdev, } #endif -#ifdef CONFIG_TRANSPARENT_HUGEPAGE +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_BROKEN) int dax_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *, unsigned int flags, get_block_t); int __dax_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *, -- 2.6.6