On Tue, Feb 11, 2020 at 04:34:01PM +1100, Dave Chinner wrote: > 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 ah... yea emulate is a bad word here. > - 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. How about? <commit msg> fs: Remove unneeded IS_DAX() check 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 has it's own read/write methods and file systems which support DAX check IS_DAX() prior to IOCB_DIRECT. Therefore, it does not matter if the file state is DAX when the iocb flags are created, and we can avoid the race. Reviewed-by: Jan Kara <jack@xxxxxxx> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx> </commit msg> Ira > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx
