From: Ross Zwisler Subject: Re: [PATCH 13/18] dax: Make huge page handling depend of CONFIG_BROKEN Date: Fri, 29 Apr 2016 13:53:40 -0600 Message-ID: <20160429195340.GG5888@linux.intel.com> References: <1461015341-20153-1-git-send-email-jack@suse.cz> <1461015341-20153-14-git-send-email-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org, Ross Zwisler , Dan Williams , linux-nvdimm@lists.01.org, Matthew Wilcox To: Jan Kara Return-path: Content-Disposition: inline In-Reply-To: <1461015341-20153-14-git-send-email-jack@suse.cz> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On Mon, Apr 18, 2016 at 11:35:36PM +0200, Jan Kara wrote: > 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 Ah, sorry, I think by "make PMD depend on CONFIG_BROKEN" Dan & I meant this: diff --git a/fs/Kconfig b/fs/Kconfig index 6725f59..b8fcb41 100644 --- a/fs/Kconfig +++ b/fs/Kconfig @@ -52,6 +52,7 @@ config FS_DAX_PMD depends on FS_DAX depends on ZONE_DEVICE depends on TRANSPARENT_HUGEPAGE + depends on BROKEN endif # BLOCK This has the benefit that you have only one place to quickly reenable PMD code if/when we want to work on it. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org