On Fri, Apr 07, 2017 at 06:34:28AM -0500, Goldwyn Rodrigues wrote:
>
>
> On 04/06/2017 05:54 PM, Darrick J. Wong wrote:
> > On Mon, Apr 03, 2017 at 11:52:11PM -0700, Christoph Hellwig wrote:
> >>> + if (unaligned_io) {
> >>> + /* If we are going to wait for other DIO to finish, bail */
> >>> + if ((iocb->ki_flags & IOCB_NOWAIT) &&
> >>> + atomic_read(&inode->i_dio_count))
> >>> + return -EAGAIN;
> >>> inode_dio_wait(inode);
> >>
> >> This checks i_dio_count twice in the nowait case, I think it should be:
> >>
> >> if (iocb->ki_flags & IOCB_NOWAIT) {
> >> if (atomic_read(&inode->i_dio_count))
> >> return -EAGAIN;
> >> } else {
> >> inode_dio_wait(inode);
> >> }
> >>
> >>> if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) {
> >>> if (flags & IOMAP_DIRECT) {
> >>> + /* A reflinked inode will result in CoW alloc */
> >>> + if (flags & IOMAP_NOWAIT) {
> >>> + error = -EAGAIN;
> >>> + goto out_unlock;
> >>> + }
> >>
> >> This is a bit pessimistic - just because the inode has any shared
> >> extents we could still write into unshared ones. For now I think this
> >> pessimistic check is fine, but the comment should be corrected.
> >
> > Consider what happens in both _reflink_{allocate,reserve}_cow. If there
> > is already an existing reservation in the CoW fork then we'll have to
> > CoW and therefore can't satisfy the NOWAIT flag. If there isn't already
> > anything in the CoW fork, then we have to see if there are shared blocks
> > by calling _reflink_trim_around_shared. That performs a refcountbt
> > lookup, which involves locking the AGF, so we also can't satisfy NOWAIT.
> >
> > IOWs, I think this hunk has to move outside the IOMAP_DIRECT check to
> > cover both write-to-reflinked-file cases.
> >
>
> IOMAP_NOWAIT is set only with IOMAP_DIRECT since the nowait feature is
> for direct-IO only. This is checked early on, when we are checking for
Ah, ok. Disregard what I said about moving it then.
--D
> user-passed flags, and if not, -EINVAL is returned.
>
>
> --
> Goldwyn
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