From: Trond Myklebust <trondmy@hammerspace.com>
To: "bcodding@redhat.com" <bcodding@redhat.com>,
"chuck.lever@oracle.com" <chuck.lever@oracle.com>
Cc: "tibbs@math.uh.edu" <tibbs@math.uh.edu>,
"bfields@fieldses.org" <bfields@fieldses.org>,
"linux@stwm.de" <linux@stwm.de>,
"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"km@cm4all.com" <km@cm4all.com>
Subject: Re: Regression in 5.1.20: Reading long directory fails
Date: Thu, 12 Sep 2019 12:53:16 +0000 [thread overview]
Message-ID: <c8bc4f95e7a097b01e5fff9ce5324e32ee9d8821.camel@hammerspace.com> (raw)
In-Reply-To: <EC2B51FB-8C22-4513-B59F-0F0741F694EB@redhat.com>
On Thu, 2019-09-12 at 08:29 -0400, Benjamin Coddington wrote:
> On 11 Sep 2019, at 13:54, Chuck Lever wrote:
>
> > > On Sep 11, 2019, at 1:50 PM, Benjamin Coddington
> > > <bcodding@redhat.com> wrote:
> > >
> > > On 11 Sep 2019, at 13:40, Benjamin Coddington wrote:
> > >
> > > > On 11 Sep 2019, at 13:29, Chuck Lever wrote:
> > > >
> > > > > > On Sep 11, 2019, at 1:26 PM, Benjamin Coddington
> > > > > > <bcodding@redhat.com> wrote:
> > > > > >
> > > > > >
> > > > > > On 11 Sep 2019, at 12:39, Chuck Lever wrote:
> > > > > >
> > > > > > > > On Sep 11, 2019, at 12:25 PM, Benjamin Coddington
> > > > > > > > <bcodding@redhat.com> wrote:
> > > > > > > >
> > > > > > > > Instead, I think we want to make sure the mic falls
> > > > > > > > squarely
> > > > > > > > into the tail
> > > > > > > > every time.
> > > > > > >
> > > > > > > I'm not clear how you could do that. The length of the
> > > > > > > page data
> > > > > > > is not
> > > > > > > known to the client before it parses the reply. Are you
> > > > > > > suggesting that
> > > > > > > gss_unwrap should do it somehow?
> > > > > >
> > > > > > Is it too niave to always put the mic at the end of the
> > > > > > tail?
> > > > >
> > > > > The size of the page content is variable.
> > > > >
> > > > > The only way the MIC will fall into the tail is if the page
> > > > > content
> > > > > is
> > > > > exactly the largest expected size. When the page content is
> > > > > smaller
> > > > > than
> > > > > that, the receive logic will place part or all of the MIC in
> > > > > ->pages.
> > > >
> > > > Ok, right. But what I meant is that xdr_buf_read_netobj()
> > > > should be
> > > > renamed
> > > > and repurposed to be "move the mic from wherever it is to the
> > > > end of
> > > > xdr_buf's tail".
> > > >
> > > > But now I see what you mean, and I also see that it is already
> > > > trying to do
> > > > that.. and we don't want to overlap the copy..
> > > >
> > > > So, really, we need the tail to be larger than twice the mic..
> > > > less
> > > > 1. That
> > > > means the fix is probably just increasing rslack for krb5i.
> > >
> > > .. or we can keep the tighter tail space, and if we detect the
> > > mic
> > > straddles
> > > the page and tail, we can move the mic into the tail with 2
> > > copies,
> > > first
> > > move the bit in the tail back, then move the bit in the pages.
> > >
> > > Which is preferred, less allocation, or in the rare case this
> > > occurs,
> > > doing
> > > copy twice?
> >
> > It sounds like the bug is that the current code does not deal
> > correctly
> > when the MIC crosses the boundary between ->pages and ->tail? I'd
> > like
> > to see that addressed rather than changing rslack.
>
> Here's what I'm about to run through my testing:
>
> diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> index 48c93b9e525e..d6ffc9011269 100644
> --- a/net/sunrpc/xdr.c
> +++ b/net/sunrpc/xdr.c
> @@ -1238,14 +1238,21 @@ EXPORT_SYMBOL_GPL(xdr_encode_word);
>
> /* If the netobj starting offset bytes from the start of xdr_buf
> is
> contained
> * entirely in the head or the tail, set object to point to it;
> otherwise
> - * try to find space for it at the end of the tail, copy it there,
> and
> - * set obj to point to it. */
> + * try to find space for it at the end of the tail, and copy it
> there.
> If
> + * the netobj is partly within the page data and tail, shrink the
> pages
> to
> + * move the object into the tail */
> int xdr_buf_read_netobj(struct xdr_buf *buf, struct xdr_netobj
> *obj,
> unsigned int offset)
> {
> struct xdr_buf subbuf;
> + unsigned int page_range;
>
> if (xdr_decode_word(buf, offset, &obj->len))
> return -EFAULT;
> +
> + page_range = buf->head->iov_len + buf->page_len - offset + 4;
> + if (page_range > 0 && page_range < obj->len)
> + xdr_shrink_pagelen(buf, page_range);
> +
> if (xdr_buf_subsegment(buf, &subbuf, offset + 4, obj->len))
> return -EFAULT;
>
>
Let's please just scrap this function and rewrite it as a generic
function for reading the MIC. It clearly is not a generic function for
reading arbitrary netobjs, and modifications like the above just make
the misnomer painfully obvious.
Let's rewrite it as xdr_buf_read_mic() so that we can simplify it where
possible.
Thanks
Trond
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com
next prev parent reply other threads:[~2019-09-12 12:53 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-13 15:08 Regression in 5.1.20: Reading long directory fails Jason L Tibbitts III
2019-08-13 17:00 ` Jason L Tibbitts III
2019-08-22 19:39 ` Jason L Tibbitts III
2019-08-28 17:46 ` J. Bruce Fields
2019-08-28 18:29 ` Jason L Tibbitts III
2019-08-28 18:33 ` J. Bruce Fields
2019-09-03 15:49 ` Jason L Tibbitts III
2019-09-03 18:02 ` Wolfgang Walter
2019-09-03 19:06 ` Jason L Tibbitts III
2019-09-03 19:08 ` Chuck Lever
2019-09-03 21:37 ` Wolfgang Walter
2019-09-04 1:50 ` Jason L Tibbitts III
2019-09-06 14:48 ` J. Bruce Fields
2019-09-06 20:47 ` Jason L Tibbitts III
2019-09-06 20:50 ` Chuck Lever
2019-09-08 11:39 ` Benjamin Coddington
2019-09-08 15:19 ` Trond Myklebust
2019-09-08 15:48 ` Chuck Lever
2019-09-08 16:47 ` Trond Myklebust
2019-09-08 16:51 ` Chuck Lever
2019-09-11 16:25 ` Benjamin Coddington
2019-09-11 16:39 ` Chuck Lever
2019-09-11 17:26 ` Benjamin Coddington
2019-09-11 17:27 ` Benjamin Coddington
2019-09-11 17:29 ` Chuck Lever
2019-09-11 17:40 ` Benjamin Coddington
2019-09-11 17:43 ` Chuck Lever
2019-09-11 17:59 ` Benjamin Coddington
2019-09-11 17:50 ` Benjamin Coddington
2019-09-11 17:54 ` Chuck Lever
2019-09-12 12:29 ` Benjamin Coddington
2019-09-12 12:53 ` Trond Myklebust [this message]
2019-09-12 13:08 ` Benjamin Coddington
2019-09-12 13:13 ` J. Bruce Fields
2019-09-12 13:25 ` Trond Myklebust
2019-09-12 13:35 ` Benjamin Coddington
2019-09-12 13:14 ` Trond Myklebust
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=c8bc4f95e7a097b01e5fff9ce5324e32ee9d8821.camel@hammerspace.com \
--to=trondmy@hammerspace.com \
--cc=bcodding@redhat.com \
--cc=bfields@fieldses.org \
--cc=chuck.lever@oracle.com \
--cc=km@cm4all.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-nfs@vger.kernel.org \
--cc=linux@stwm.de \
--cc=tibbs@math.uh.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).