From 12735f881952c32b31bc4e433768f18489f79ec9 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Fri, 13 May 2016 00:51:15 -0400 Subject: ext4: pre-zero allocated blocks for DAX IO Currently ext4 treats DAX IO the same way as direct IO. I.e., it allocates unwritten extents before IO is done and converts unwritten extents afterwards. However this way DAX IO can race with page fault to the same area: ext4_ext_direct_IO() dax_fault() dax_io() get_block() - allocates unwritten extent copy_from_iter_pmem() get_block() - converts unwritten block to written and zeroes it out ext4_convert_unwritten_extents() So data written with DAX IO gets lost. Similarly dax_new_buf() called from dax_io() can overwrite data that has been already written to the block via mmap. Fix the problem by using pre-zeroed blocks for DAX IO the same way as we use them for DAX mmap. The downside of this solution is that every allocating write writes each block twice (once zeros, once data). Fixing the race with locking is possible as well however we would need to lock-out faults for the whole range written to by DAX IO. And that is not easy to do without locking-out faults for the whole file which seems too aggressive. Signed-off-by: Jan Kara Signed-off-by: Theodore Ts'o --- fs/ext4/ext4.h | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'fs/ext4/ext4.h') diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 89e1bcb21341..b84aa1ca480a 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -2527,8 +2527,8 @@ struct buffer_head *ext4_getblk(handle_t *, struct inode *, ext4_lblk_t, int); struct buffer_head *ext4_bread(handle_t *, struct inode *, ext4_lblk_t, int); int ext4_get_block_unwritten(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create); -int ext4_dax_mmap_get_block(struct inode *inode, sector_t iblock, - struct buffer_head *bh_result, int create); +int ext4_dax_get_block(struct inode *inode, sector_t iblock, + struct buffer_head *bh_result, int create); int ext4_get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create); int ext4_dio_get_block(struct inode *inode, sector_t iblock, @@ -3334,6 +3334,13 @@ static inline void ext4_clear_io_unwritten_flag(ext4_io_end_t *io_end) } } +static inline bool ext4_aligned_io(struct inode *inode, loff_t off, loff_t len) +{ + int blksize = 1 << inode->i_blkbits; + + return IS_ALIGNED(off, blksize) && IS_ALIGNED(len, blksize); +} + #endif /* __KERNEL__ */ #define EFSBADCRC EBADMSG /* Bad CRC detected */ -- cgit v1.2.3