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

[Dave Wysochanski <dwysocha@redhat.com>]

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)
-		nfs_pageio_complete_read(&desc.pgio);
+	ret = nfs_pageio_complete_read(&desc.pgio);
+	if (ret)
+		goto out;
+
+	ret = wait_on_page_locked_killable(page);
+	if (!PageUptodate(page) && !ret)
+		ret = xchg(&desc.ctx->error, 0);
 
-	ret = desc.pgio.pg_error < 0 ? desc.pgio.pg_error : 0;
-	if (!ret) {
-		ret = wait_on_page_locked_killable(page);
-		if (!PageUptodate(page) && !ret)
-			ret = xchg(&desc.ctx->error, 0);
-	}
 out:
 	put_nfs_open_context(desc.ctx);
 	return ret;
-- 
1.8.3.1