On Sat, Feb 08, 2020 at 11:34:38AM -0800, ira.weiny@xxxxxxxxx wrote: > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > The IS_DAX() check in io_is_direct() causes a race between changing the > DAX state and creating the iocb flags. > > Remove the check because DAX now emulates the page cache API and > therefore it does not matter if the file state is DAX or not when the > iocb flags are created. This statement is ... weird. DAX doesn't "emulate" the page cache API at all - it has it's own read/write methods that filesystems call based on the iomap infrastructure (dax_iomap_rw()). i.e. there are 3 different IO paths through the filesystems: the DAX IO path, the direct IO path, and the buffered IO path. Indeed, it seems like this works a bit by luck: Ext4 and XFS always check IS_DAX(inode) in the read/write_iter methods before checking for IOCB_DIRECT, and hence the IOCB_DIRECT flag is ignored by the filesystems. i.e. when we got rid of the O_DIRECT paths from DAX, we forgot to clean up io_is_direct() and it's only due to the ordering of checks that we went down the DAX path correctly.... That said, the code change is good, but the commit message needs a rewrite. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
