| Message ID | 1463070560-1979-3-git-send-email-jack@suse.cz (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 348e967ab07c |
| Headers | show |
On Thu, May 12, 2016 at 06:29:15PM +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 <jack@suse.cz> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
diff --git a/fs/Kconfig b/fs/Kconfig index 6725f59c18e6..b8fcb416be72 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 diff --git a/fs/dax.c b/fs/dax.c index d7addfab2094..ef44ee2af7af 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) /* * 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..3be567e3ae9c 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) 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 *,
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 <jack@suse.cz> --- fs/Kconfig | 1 + fs/dax.c | 2 +- include/linux/dax.h | 2 +- 3 files changed, 3 insertions(+), 2 deletions(-)