Hi Su,
On Mon, 2019-09-30 at 17:11 +0800, Su Yanjun wrote:
> 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@xxxxxxxxxxxxxx>
> ---
> 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);
>
Thanks for looking into this issue. I agree with your analysis of what
is going wrong in generic/465.
However, I think the problem is greater than just EOF. I think we also
need to look at the generic error handling, and ensure that it handles
a truncated RPC call in the middle of a series of calls correctly.
Please see the two patches I sent you just now and check if they fix
the problem for you.
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
