On Tue, Nov 24, 2020 at 10:40:25PM +0000, Kornievskaia, Olga wrote:
>
>
> On 11/24/20, 4:20 PM, "Frank van der Linden" <fllinden@xxxxxxxxxx> wrote:
>
> On Tue, Nov 24, 2020 at 08:50:36PM +0000, Kornievskaia, Olga wrote:
> >
> >
> > On 11/24/20, 3:06 PM, "Frank van der Linden" <fllinden@xxxxxxxxxx> wrote:
> >
> > On Tue, Nov 24, 2020 at 12:26:32PM -0500, Chuck Lever wrote:
> > >
> > >
> > >
> > > By switching to an XFS-backed export, I am able to reproduce the
> > > ibcomp worker crash on my client with xfstests generic/013.
> > >
> > > For the failing LISTXATTRS operation, xdr_inline_pages() is called
> > > with page_len=12 and buflen=128. Then:
> > >
> > > - Because buflen is small, rpcrdma_marshal_req will not set up a
> > > Reply chunk and the rpcrdma's XDRBUF_SPARSE_PAGES logic does not
> > > get invoked at all.
> > >
> > > - Because page_len is non-zero, rpcrdma_inline_fixup() tries to
> > > copy received data into rq_rcv_buf->pages, but they're missing.
> > >
> > > The result is that the ibcomp worker faults and dies. Sometimes that
> > > causes a visible crash, and sometimes it results in a transport
> > > hang without other symptoms.
> > >
> > > RPC/RDMA's XDRBUF_SPARSE_PAGES support is not entirely correct, and
> > > should eventually be fixed or replaced. However, my preference is
> > > that upper-layer operations should explicitly allocate their receive
> > > buffers (using GFP_KERNEL) when possible, rather than relying on
> > > XDRBUF_SPARSE_PAGES.
> > >
> > > Reported-by: Olga kornievskaia <kolga@xxxxxxxxxx>
> > > Suggested-by: Olga kornievskaia <kolga@xxxxxxxxxx>
> > > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> > > ---
> > > fs/nfs/nfs42proc.c | 17 ++++++++++-------
> > > fs/nfs/nfs42xdr.c | 1 -
> > > 2 files changed, 10 insertions(+), 8 deletions(-)
> > >
> > > Hi-
> > >
> > > I like Olga's proposed approach. What do you think of this patch?
> > >
> > >
> > > diff --git a/fs/nfs/nfs42proc.c b/fs/nfs/nfs42proc.c
> > > index 2b2211d1234e..24810305ec1c 100644
> > > --- a/fs/nfs/nfs42proc.c
> > > +++ b/fs/nfs/nfs42proc.c
> > > @@ -1241,7 +1241,7 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
> > > .rpc_resp = &res,
> > > };
> > > u32 xdrlen;
> > > - int ret, np;
> > > + int ret, np, i;
> > >
> > >
> > > res.scratch = alloc_page(GFP_KERNEL);
> > > @@ -1253,10 +1253,14 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
> > > xdrlen = server->lxasize;
> > > np = xdrlen / PAGE_SIZE + 1;
> > >
> > > + ret = -ENOMEM;
> > > pages = kcalloc(np, sizeof(struct page *), GFP_KERNEL);
> > > - if (pages == NULL) {
> > > - __free_page(res.scratch);
> > > - return -ENOMEM;
> > > + if (pages == NULL)
> > > + goto out_free;
> > > + for (i = 0; i < np; i++) {
> > > + pages[i] = alloc_page(GFP_KERNEL);
> > > + if (!pages[i])
> > > + goto out_free;
> > > }
> > >
> > > arg.xattr_pages = pages;
> > > @@ -1271,14 +1275,13 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
> > > *eofp = res.eof;
> > > }
> > >
> > > +out_free:
> > > while (--np >= 0) {
> > > if (pages[np])
> > > __free_page(pages[np]);
> > > }
> > > -
> > > - __free_page(res.scratch);
> > > kfree(pages);
> > > -
> > > + __free_page(res.scratch);
> > > return ret;
> > >
> > > }
> > > diff --git a/fs/nfs/nfs42xdr.c b/fs/nfs/nfs42xdr.c
> > > index 6e060a88f98c..8432bd6b95f0 100644
> > > --- a/fs/nfs/nfs42xdr.c
> > > +++ b/fs/nfs/nfs42xdr.c
> > > @@ -1528,7 +1528,6 @@ static void nfs4_xdr_enc_listxattrs(struct rpc_rqst *req,
> > >
> > > rpc_prepare_reply_pages(req, args->xattr_pages, 0, args->count,
> > > hdr.replen);
> > > - req->rq_rcv_buf.flags |= XDRBUF_SPARSE_PAGES;
> > >
> > > encode_nops(&hdr);
> > > }
> > >
> > >
> >
> > I can see why this is the simplest and most pragmatic solution, so it's
> > fine with me.
> >
> > Why doesn't this happen with getxattr? Do we need to convert that too?
> >
> > [olga] I don't know if GETXATTR/SETXATTR works. I'm not sure what tests exercise those operations. I just ran into the fact that generic/013 wasn't passing. And I don't see that it's an xattr specific tests. I'm not sure how it ends up triggering is usage of xattr.
>
> I'm attaching the test program I used, it should give things a better workout.
>
> [olga] I'm not sure if I'm doing something wrong but there are only 2 GETXATTR call on the network trace from running this application and both calls are returning an error (ERR_NOXATTR). Which btw might explain why no problems are seen since no decoding of data is happening. There are lots of SETXATTRs and REMOVEXATTR and there is a LISTXATTR (which btw network trace is marking as malformed so there might something bad there). Anyway...
>
> This is my initial report: no real exercise of the GETXATTR code as far as I can tell.
True, the test is heavier on the setxattr / listxattr side. And with caching,
you're not going to see a lot of GETXATTR calls. I used the same test program
with caching off, and it works fine, though.
In any case, after converting GETXATTR to pre-allocate pages, I noticed that,
when I disabled caching, I was getting EIO instead of ERANGE back from
calls that test the case of calling getxattr() with a buffer length that
is insufficient. The behavior is somewhat strange - if you, say, set an xattr
of length 59, then calls with lengths 56-59 get -ERANGE from decode_getxattr
(correct), but calls with lengths 53-55 get EIO (should be -ERANGE).
E.g. non-aligned values to rpc_prepare_reply_pages make the RPC call error
out early, even before it gets to decode_getxattr.
I noticed that all other code always seems to specify multiples of PAGE_SIZE
as the length to rpc_prepare_reply_pages. But the code itself suggests that
it certainly *intends* to be prepared to handle any length, aligned or not.
However, apparently, it at least doesn't deal with non-aligned lengths,
making things fail further along down the line.
I need to look at this a bit more.
- Frank
