Re: [PATCH] NFS: Fix O_DIRECT read problem when another write is going on

[Su Yanjun]

å 2019/10/1 2:06, Trond Myklebust åé:
> 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.

The patchset you sent works for generic/465.

Thanks a lot