On Wed 11-05-16 21:23:12, Eryu Guan wrote:
> On Tue, May 10, 2016 at 01:38:05PM -0400, Jeff Moyer wrote:
> > Look, I think this is all you need for the full fix:
> >
> > diff --git a/fs/direct-io.c b/fs/direct-io.c
> > index 4720377..f66754e 100644
> > --- a/fs/direct-io.c
> > +++ b/fs/direct-io.c
> > @@ -639,8 +639,7 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
> > */
> > create = dio->rw & WRITE;
> > if (dio->flags & DIO_SKIP_HOLES) {
> > - if (sdio->block_in_file < (i_size_read(dio->inode) >>
> > - sdio->blkbits))
> > + if (fs_startblk < fs_count)
fs_count is number of blocks in the request so that is not correct...
> > create = 0;
> > }
> >
> >
> > Can you just test that?
>
> I tested it and it did fix both of the issues for me. But it seems that
> it's a bit overkilled, in certain case block allocation should be
> allowed, but it still sets 'create' to 0.
>
> For example, append writing 8k to a 4k sparse file (so offset is also
> 4k), on a 4k block size filesystem, fs_startblk(1) is smaller than
> fs_count(2), so it still sets 'create' to 0. But block allocation should
> be allowed in this case, and both the original code and my patch do so.
>
> So I simplified my real fix to this (updates for comments not included):
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 4720377..0cace3e 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -639,8 +639,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
> */
> create = dio->rw & WRITE;
> if (dio->flags & DIO_SKIP_HOLES) {
> - if (sdio->block_in_file < (i_size_read(dio->inode) >>
> - sdio->blkbits))
> + if (fs_startblk <= ((i_size_read(dio->inode) - 1) >>
> + i_blkbits))
> create = 0;
Yes, this is correct as far as I can tell.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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