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

On Mon, Jun 28, 2021 at 3:17 PM Trond Myklebust
[off-list ref] wrote:

quoted

On Mon, 2021-06-28 at 13:39 -0400, Dave Wysochanski wrote:

quoted

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 <redacted>
---
 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);