Re: [PATCH 2/4] NFS: Ensure nfs_readpage returns promptly when internal error occurs

David Wysochanski
2021-06-28T20:01:35Z

On Mon, Jun 28, 2021 at 3:17 PM Trond Myklebust <trondmy@hammerspace.com> wrote:
>
> On Mon, 2021-06-28 at 13:39 -0400, Dave Wysochanski wrote:
> > A previous refactoring of nfs_readpage() might end up calling
> > wait_on_page_locked_killable() even if readpage_async_filler() failed
> > with an internal error and pg_error was non-zero (for example, if
> > nfs_create_request() failed). In the case of an internal error,
> > skip over wait_on_page_locked_killable() as this is only needed
> > when the read is sent and an error occurs during completion handling.
> >
> > Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
> > ---
> > fs/nfs/read.c | 21 ++++++++++++---------
> > 1 file changed, 12 insertions(+), 9 deletions(-)
> >
> > diff --git a/fs/nfs/read.c b/fs/nfs/read.c
> > index 684a730f6670..b0680351df23 100644
> > --- a/fs/nfs/read.c
> > +++ b/fs/nfs/read.c
> > @@ -74,7 +74,7 @@ void nfs_pageio_init_read(struct
> > nfs_pageio_descriptor *pgio,
> > }
> > EXPORT_SYMBOL_GPL(nfs_pageio_init_read);
> >
> > -static void nfs_pageio_complete_read(struct nfs_pageio_descriptor
> > *pgio)
> > +static int nfs_pageio_complete_read(struct nfs_pageio_descriptor
> > *pgio)
> > {
> > struct nfs_pgio_mirror *pgm;
> > unsigned long npages;
> > @@ -88,6 +88,8 @@ static void nfs_pageio_complete_read(struct
> > nfs_pageio_descriptor *pgio)
> > NFS_I(pgio->pg_inode)->read_io += pgm->pg_bytes_written;
> > npages = (pgm->pg_bytes_written + PAGE_SIZE - 1) >>
> > PAGE_SHIFT;
> > nfs_add_stats(pgio->pg_inode, NFSIOS_READPAGES, npages);
> > +
> > + return pgio->pg_error < 0 ? pgio->pg_error : 0;
> > }
> >
> >
> > @@ -373,16 +375,17 @@ int nfs_readpage(struct file *file, struct page
> > *page)
> > &nfs_async_read_completion_ops);
> >
> > ret = readpage_async_filler(&desc, page);
> > + if (ret)
> > + goto out;
> >
> > - if (!ret)
>
> Can't this patch basically be reduced to the above 2 changes? The rest
> appears just to be shifting code around. I'm seeing nothing in the
> remaining patches that actually depends on nfs_pageio_complete_read()
> returning a value.
>

Originally I was thinking there was a benefit to having
nfs_pageio_complete_read return a success/failure
similar to readpage_async_filler() which is why I moved
it.

You mean just this right? If so, yes I agree this would be a minimal patch.
Want this as a v2?

diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index 684a730f6670..eb390eb618b3 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -373,10 +373,10 @@ int nfs_readpage(struct file *file, struct page *page)
&nfs_async_read_completion_ops);

ret = readpage_async_filler(&desc, page);
+ if (ret)
+ goto out;

- if (!ret)
- nfs_pageio_complete_read(&desc.pgio);
-
+ nfs_pageio_complete_read(&desc.pgio);
ret = desc.pgio.pg_error < 0 ? desc.pgio.pg_error : 0;
if (!ret) {
ret = wait_on_page_locked_killable(page);