The ext4 DIO code releases the mutex for overwrite before the actual write I/O. This doesn't work well for DAX as the filemap_write_and_wait_range() function can't prevent the overwrites from stepping on each other. This is due to the fact that DAX I/Os are synchronous and no filemap information on which I/O operations are pending is stored. This patch prevents the ext4 DIO code from releasing the i_mutex when in DAX mode. It also disable updating the i_dio_count as the i_mutex will be hold for the entire duration of the write. Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx> --- fs/ext4/inode.c | 27 ++++++++++++++++++--------- 1 files changed, 18 insertions(+), 9 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index dab84a2..252731e 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -3347,6 +3347,7 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter, get_block_t *get_block_func = NULL; int dio_flags = 0; loff_t final_size = offset + count; + bool update_dio_count, is_dax = IS_DAX(inode); /* Use the old path for reads and writes beyond i_size. */ if (iov_iter_rw(iter) != WRITE || final_size > inode->i_size) @@ -3355,17 +3356,25 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter, BUG_ON(iocb->private == NULL); /* + * If we do a overwrite dio, i_mutex locking can be released. + * For DAX, however, we shouldn't release the lock as the + * filemap_write_and_wait_range() function can't protect the + * overwrite from stepping on each other. + */ + overwrite = *((int *)iocb->private); + + /* * Make all waiters for direct IO properly wait also for extent * conversion. This also disallows race between truncate() and * overwrite DIO as i_dio_count needs to be incremented under i_mutex. + * For DAX, we don't need to update the i_dio_count as we will keep + * the i_mutex for the duration of the I/O operation. */ - if (iov_iter_rw(iter) == WRITE) + update_dio_count = (iov_iter_rw(iter) == WRITE) && !is_dax; + if (update_dio_count) inode_dio_begin(inode); - /* If we do a overwrite dio, i_mutex locking can be released */ - overwrite = *((int *)iocb->private); - - if (overwrite) + if (overwrite && !is_dax) inode_unlock(inode); /* @@ -3401,7 +3410,7 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter, #ifdef CONFIG_EXT4_FS_ENCRYPTION BUG_ON(ext4_encrypted_inode(inode) && S_ISREG(inode->i_mode)); #endif - if (IS_DAX(inode)) + if (is_dax) ret = dax_do_io(iocb, inode, iter, offset, get_block_func, ext4_end_io_dio, dio_flags); else @@ -3424,10 +3433,10 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter, ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN); } - if (iov_iter_rw(iter) == WRITE) + if (update_dio_count) inode_dio_end(inode); - /* take i_mutex locking again if we do a ovewrite dio */ - if (overwrite) + /* take i_mutex locking again if we do a non-DAX ovewrite dio */ + if (overwrite && !is_dax) inode_lock(inode); return ret; -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
