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 <[email protected]> > --- > 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 [email protected]
