Re: [PATCH 0/10 v13] merge request: No wait AIO

[Christoph Hellwig <hch@lst.de>]

On Tue, Jun 20, 2017 at 01:24:28AM +0100, Al Viro wrote:
> On Mon, Jun 19, 2017 at 05:36:05PM -0600, Jens Axboe wrote:
> > On 06/19/2017 05:34 PM, Al Viro wrote:
> > > On Mon, Jun 19, 2017 at 05:15:16PM -0600, Jens Axboe wrote:
> > >> On 06/19/2017 10:33 AM, Goldwyn Rodrigues wrote:
> > >>> Jens,
> > >>>
> > >>> As Christoph suggested, I am sending the patches against the block
> > >>> tree for merge since the block layer changes had the most conflicts.
> > >>> My tree is at https://github.com/goldwynr/linux/tree/nowait-block
> > >>
> > >> I can merge it for 4.13, but I need Al to be happy with it first.
> > > 
> > > FWIW, it's really a matter of who gets more conflicts - I'm OK with the
> > > general shape of that code and it could go through either tree (or both,
> > > for that matter, if an immutable branch is promised).
> > 
> > I'm still hopeful that the write hint patchset will make it as well,
> > which will definitely conflict with this. So if you don't mind, I'd
> > like to queue it through the block tree. The block for-4.x/ branches
> > are not rebased.
> 
> Fine by me; the only problem I see there at the moment is with ext4 and
> xfs ->read_iter() not buggering off on nowait (xfs one has
>         xfs_ilock(ip, XFS_IOLOCK_SHARED);
> done before it gets to generic_file_read_iter()).

Something like the patch below should take care of the XFS, free feel
to fold.


diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index e159eb381d9f..c74847f71b3d 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -216,7 +216,11 @@ xfs_file_dio_aio_read(
 
 	file_accessed(iocb->ki_filp);
 
-	xfs_ilock(ip, XFS_IOLOCK_SHARED);
+	if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED)) {
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			return -EAGAIN;
+		xfs_ilock(ip, XFS_IOLOCK_SHARED);
+	}
 	ret = iomap_dio_rw(iocb, to, &xfs_iomap_ops, NULL);
 	xfs_iunlock(ip, XFS_IOLOCK_SHARED);
 
@@ -237,7 +241,11 @@ xfs_file_dax_read(
 	if (!count)
 		return 0; /* skip atime */
 
-	xfs_ilock(ip, XFS_IOLOCK_SHARED);
+	if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED)) {
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			return -EAGAIN;
+		xfs_ilock(ip, XFS_IOLOCK_SHARED);
+	}
 	ret = dax_iomap_rw(iocb, to, &xfs_iomap_ops);
 	xfs_iunlock(ip, XFS_IOLOCK_SHARED);