linux-kernel - [PATCH] NFS: Fix O_DIRECT read problem when another write is going on

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Date:   Mon, 30 Sep 2019 17:11:18 +0800
From:   Su Yanjun <suyj.fnst@...fujitsu.com>
To:     <trond.myklebust@...merspace.com>
CC:     <linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <suyj.fnst@...fujitsu.com>
Subject: [PATCH] NFS: Fix O_DIRECT read problem when another write is going on

In xfstests generic/465 tests failed. Because O_DIRECT r/w use
async rpc calls, when r/w rpc calls are running concurrently we
may read partial data which is wrong.

For example as follows.
 user buffer
/--------\
|    |XXXX|
 rpc0 rpc1

When rpc0 runs it encounters eof so return 0, then another writes
something. When rpc1 runs it returns some data. The total data
buffer contains wrong data.

In this patch we check eof mark for each direct request. If encounters
eof then set eof mark in the request, when we meet it again report
-EAGAIN error. In nfs_direct_complete we convert -EAGAIN as if read
nothing. When the reader issue another read it will read ok.

Signed-off-by: Su Yanjun <suyj.fnst@...fujitsu.com>
---
 fs/nfs/direct.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 222d711..7f737a3 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -93,6 +93,7 @@ struct nfs_direct_req {
 				bytes_left,	/* bytes left to be sent */
 				error;		/* any reported error */
 	struct completion	completion;	/* wait for i/o completion */
+	int			eof;		/* eof mark in the req */
 
 	/* commit state */
 	struct nfs_mds_commit_info mds_cinfo;	/* Storage for cinfo */
@@ -380,6 +381,12 @@ static void nfs_direct_complete(struct nfs_direct_req *dreq)
 {
 	struct inode *inode = dreq->inode;
 
+	/* read partial data just as read nothing */
+	if (dreq->error == -EAGAIN) {
+		dreq->count = 0;
+		dreq->error = 0;
+	}
+
 	inode_dio_end(inode);
 
 	if (dreq->iocb) {
@@ -413,8 +420,13 @@ static void nfs_direct_read_completion(struct nfs_pgio_header *hdr)
 	if (hdr->good_bytes != 0)
 		nfs_direct_good_bytes(dreq, hdr);
 
-	if (test_bit(NFS_IOHDR_EOF, &hdr->flags))
+	if (dreq->eof)
+		dreq->error = -EAGAIN;
+
+	if (test_bit(NFS_IOHDR_EOF, &hdr->flags)) {
 		dreq->error = 0;
+		dreq->eof = 1;
+	}
 
 	spin_unlock(&dreq->lock);
 
-- 
2.7.4