Re: [PATCH] NFSv4.2: improve page handling for GETXATTR

From: Frank van der Linden <fllinden@amazon.com>
To: Olga Kornievskaia <aglo@umich.edu>
Cc: linux-nfs <linux-nfs@vger.kernel.org>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	Chuck Lever <chuck.lever@oracle.com>
Subject: Re: [PATCH] NFSv4.2: improve page handling for GETXATTR
Date: Tue, 1 Dec 2020 22:24:11 +0000	[thread overview]
Message-ID: <20201201222411.GA16772@dev-dsk-fllinden-2c-c1893d73.us-west-2.amazon.com> (raw)
In-Reply-To: <CAN-5tyF8P9J8DhHZhFyEq97BpjAe9bFg786QH6eF_1r0jPi-Fg@mail.gmail.com>

On Tue, Dec 01, 2020 at 05:03:46PM -0500, Olga Kornievskaia wrote:
> 
> On Tue, Dec 1, 2020 at 4:44 PM Frank van der Linden <fllinden@amazon.com> wrote:
> >
> > XDRBUF_SPARSE_PAGES can cause problems for the RDMA transport,
> > and it's easy enough to allocate enough pages for the request
> > up front, so do that.
> >
> > Also, since we've allocated the pages anyway, use the full
> > page aligned length for the receive buffer. This will allow
> > caching of valid replies that are too large for the caller,
> > but that still fit in the allocated pages.
> >
> > Signed-off-by: Frank van der Linden <fllinden@amazon.com>
> > ---
> >  fs/nfs/nfs42proc.c | 39 ++++++++++++++++++++++++++++++---------
> >  fs/nfs/nfs42xdr.c  | 22 +++++++++++++++++-----
> >  2 files changed, 47 insertions(+), 14 deletions(-)
> >
> > diff --git a/fs/nfs/nfs42proc.c b/fs/nfs/nfs42proc.c
> > index 2b2211d1234e..bfe15ac77bd9 100644
> > --- a/fs/nfs/nfs42proc.c
> > +++ b/fs/nfs/nfs42proc.c
> > @@ -1176,11 +1176,9 @@ static ssize_t _nfs42_proc_getxattr(struct inode *inode, const char *name,
> >                                 void *buf, size_t buflen)
> >  {
> >         struct nfs_server *server = NFS_SERVER(inode);
> > -       struct page *pages[NFS4XATTR_MAXPAGES] = {};
> > +       struct page **pages;
> >         struct nfs42_getxattrargs arg = {
> >                 .fh             = NFS_FH(inode),
> > -               .xattr_pages    = pages,
> > -               .xattr_len      = buflen,
> >                 .xattr_name     = name,
> >         };
> >         struct nfs42_getxattrres res;
> > @@ -1189,12 +1187,31 @@ static ssize_t _nfs42_proc_getxattr(struct inode *inode, const char *name,
> >                 .rpc_argp       = &arg,
> >                 .rpc_resp       = &res,
> >         };
> > -       int ret, np;
> > +       ssize_t ret, np, i;
> > +
> > +       arg.xattr_len = buflen ?: XATTR_SIZE_MAX;
> > +
> > +       ret = -ENOMEM;
> > +       np = DIV_ROUND_UP(arg.xattr_len, PAGE_SIZE);
> > +
> > +       pages = kcalloc(np, sizeof(struct page *), GFP_KERNEL);
> > +       if (pages == NULL)
> > +               return ret;
> > +
> > +       for (i = 0; i < np; i++) {
> > +               pages[i] = alloc_page(GFP_KERNEL);
> > +               if (!pages[i])
> > +                       goto out_free;
> > +       }
> > +
> > +       arg.xattr_pages = pages;
> >
> >         ret = nfs4_call_sync(server->client, server, &msg, &arg.seq_args,
> >             &res.seq_res, 0);
> >         if (ret < 0)
> > -               return ret;
> > +               goto out_free;
> > +
> > +       ret = res.xattr_len;
> >
> >         /*
> >          * Normally, the caching is done one layer up, but for successful
> > @@ -1209,16 +1226,20 @@ static ssize_t _nfs42_proc_getxattr(struct inode *inode, const char *name,
> >         nfs4_xattr_cache_add(inode, name, NULL, pages, res.xattr_len);
> >
> >         if (buflen) {
> > -               if (res.xattr_len > buflen)
> > -                       return -ERANGE;
> > +               if (res.xattr_len > buflen) {
> > +                       ret = -ERANGE;
> > +                       goto out_free;
> > +               }
> >                 _copy_from_pages(buf, pages, 0, res.xattr_len);
> >         }
> >
> > -       np = DIV_ROUND_UP(res.xattr_len, PAGE_SIZE);
> > +out_free:
> >         while (--np >= 0)
> >                 __free_page(pages[np]);
> 
> Looking at Chuck's page for listxattr, I think we need to check if
> (pages[np) before freeing?
> 
> Otherwise, looks fine to me. Reviewed-by.

Hm, originally, yes, because of SPARSE_PAGES use. So that was actually
a bug in the original code, which is now fixed. In other words, we
need a Cc: -stable here (which I assume we want anyway, since this
fixes RDMA).

It's not needed anymore, and it's not needed for listxattr anymore either,
although there the code was originally correct.

- Frank