Re: [PATCH 1/3] direct-io: always call ->end_io if non-NULL

Darrick J. Wong
2016-02-03T19:55:44Z

On Wed, Feb 03, 2016 at 07:40:14PM +0100, Christoph Hellwig wrote:
> This way we can pass back errors to the file system, and allow for
> cleanup required for all direct I/O invocations.
>
> Also allow the ->end_io handlers to return errors on their own, so that
> I/O completion errors can be passed on to the callers.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/dax.c | 9 +++++++--
> fs/direct-io.c | 9 +++++++--
> fs/ext4/inode.c | 9 +++++++--
> fs/ocfs2/aops.c | 7 ++++++-
> fs/xfs/xfs_aops.c | 13 +++++++------
> include/linux/fs.h | 2 +-
> 6 files changed, 35 insertions(+), 14 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 4fd6b0c..e38b2c5 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -267,8 +267,13 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
> if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
> inode_unlock(inode);
>
> - if ((retval > 0) && end_io)
> - end_io(iocb, pos, retval, bh.b_private);
> + if (end_io) {
> + int err;
> +
> + err = end_io(iocb, pos, retval, bh.b_private);
> + if (err)
> + retval = err;

This will have the effect of a later error superseding an earlier error. I'm
under the impression that code should generally preserve the first error, since
some side effect of that probably caused the rest of the errors.

That said, my guess is that 95% of the time err is set, retval and err will
both be -EIO anyway. I'm not particularly passionate about whether or not we
preserve the first error code.

> + }
>
> if (!(flags & DIO_SKIP_DIO_COUNT))
> inode_dio_end(inode);
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 1b2f7ff..9c6f885 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -253,8 +253,13 @@ static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret,
> if (ret == 0)
> ret = transferred;
>
> - if (dio->end_io && dio->result)
> - dio->end_io(dio->iocb, offset, transferred, dio->private);
> + if (dio->end_io) {
> + int err;
> +
> + err = dio->end_io(dio->iocb, offset, ret, dio->private);
> + if (err)
> + ret = err;

Same comment here. Other than that, everything vfs looks ok to me.

> + }
>
> if (!(dio->flags & DIO_SKIP_DIO_COUNT))
> inode_dio_end(dio->inode);
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 83bc8bf..9db04dd 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3161,14 +3161,17 @@ out:
> }
> #endif
>
> -static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
> +static int ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
> ssize_t size, void *private)
> {
> ext4_io_end_t *io_end = iocb->private;
>
> + if (size <= 0)
> + return 0;

This leaks the ext4_io_end_t, if there was one. Granted, that only happens
during an AIO DIO to an unwritten extent, but in any case I suggest removing
this hunk and...

> +
> /* if not async direct IO just return */
> if (!io_end)
> - return;
> + return 0;
>
> ext_debug("ext4_end_io_dio(): io_end 0x%p "
> "for inode %lu, iocb 0x%p, offset %llu, size %zd\n",
> @@ -3179,6 +3182,8 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
> io_end->offset = offset;
> io_end->size = size;

...if size < 0, then call ext4_clear_io_unwritten_flag to neutralize the ioend:

if (size < 0)
ext4_clear_io_unwritten_flag(io_end);
else
io_end->size = size;
ext4_put_io_end(io_end);
return 0;

You'll probably have to stuff ext4_clear_io_unwritten_flag into a header file;
it's currently a static function somewhere.

> ext4_put_io_end(io_end);
> +
> + return 0;
> }
>
> /*
> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
> index 794fd15..5dcc5f5 100644
> --- a/fs/ocfs2/aops.c
> +++ b/fs/ocfs2/aops.c
> @@ -620,7 +620,7 @@ bail:
> * particularly interested in the aio/dio case. We use the rw_lock DLM lock
> * to protect io on one node from truncation on another.
> */
> -static void ocfs2_dio_end_io(struct kiocb *iocb,
> +static int ocfs2_dio_end_io(struct kiocb *iocb,
> loff_t offset,
> ssize_t bytes,
> void *private)
> @@ -628,6 +628,9 @@ static void ocfs2_dio_end_io(struct kiocb *iocb,
> struct inode *inode = file_inode(iocb->ki_filp);
> int level;
>
> + if (bytes <= 0)
> + return 0;
> +

I suspect we still need to unlock the mutexes later on in this function.

> /* this io's submitter should not have unlocked this before we could */
> BUG_ON(!ocfs2_iocb_is_rw_locked(iocb));
>
> @@ -644,6 +647,8 @@ static void ocfs2_dio_end_io(struct kiocb *iocb,
> level = ocfs2_iocb_rw_locked_level(iocb);
> ocfs2_rw_unlock(inode, level);
> }

Do we need to still have an accurate value for bytes the conditional above
even if the IO errored out?

> +
> + return 0;
> }
>
> static int ocfs2_releasepage(struct page *page, gfp_t wait)
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 379c089..295aaff 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1645,7 +1645,7 @@ out_end_io:
> * case the completion can be called in interrupt context, whereas if we have an
> * ioend we will always be called in task context (i.e. from a workqueue).
> */
> -STATIC void
> +STATIC int
> xfs_end_io_direct_write(
> struct kiocb *iocb,
> loff_t offset,
> @@ -1655,15 +1655,19 @@ xfs_end_io_direct_write(
> struct inode *inode = file_inode(iocb->ki_filp);
> struct xfs_ioend *ioend = private;
>
> + if (size <= 0)
> + return 0;

Same thing here, I think we can end up leaking the ioend.

--D

> +
> trace_xfs_gbmap_direct_endio(XFS_I(inode), offset, size,
> ioend ? ioend->io_type : 0, NULL);
>
> if (!ioend) {
> ASSERT(offset + size <= i_size_read(inode));
> - return;
> + return 0;
> }
>
> __xfs_end_io_direct_write(inode, ioend, offset, size);
> + return 0;
> }
>
> static inline ssize_t
> @@ -1672,10 +1676,7 @@ xfs_vm_do_dio(
> struct kiocb *iocb,
> struct iov_iter *iter,
> loff_t offset,
> - void (*endio)(struct kiocb *iocb,
> - loff_t offset,
> - ssize_t size,
> - void *private),
> + dio_iodone_t endio,
> int flags)
> {
> struct block_device *bdev;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 1a20462..d7f37bf 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -70,7 +70,7 @@ extern int sysctl_protected_hardlinks;
> struct buffer_head;
> typedef int (get_block_t)(struct inode *inode, sector_t iblock,
> struct buffer_head *bh_result, int create);
> -typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
> +typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
> ssize_t bytes, void *private);
> typedef void (dax_iodone_t)(struct buffer_head *bh_map, int uptodate);
>
> --
> 2.1.4
>
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