netdev - Re: Weird TCP hang when doing loopback NFS (wireshark traces attached)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHQdGtQcrF4fs0Tb3jTQ6iGXzOhhjRNAezrq_eOfzo_cFxh1Xw@mail.gmail.com>
Date:	Sun, 1 Mar 2015 20:20:42 -0500
From:	Trond Myklebust <trond.myklebust@...marydata.com>
To:	Bruce James Fields <bfields@...ldses.org>
Cc:	Linux Network Devel Mailing List <netdev@...r.kernel.org>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: Weird TCP hang when doing loopback NFS (wireshark traces attached)

On Sun, Mar 1, 2015 at 8:06 PM, Bruce James Fields <bfields@...ldses.org> wrote:
> On Sun, Mar 01, 2015 at 07:52:28PM -0500, Trond Myklebust wrote:
>> Hi Bruce,
>>
>> On Sun, Mar 1, 2015 at 2:14 PM, Trond Myklebust
>> <trond.myklebust@...marydata.com> wrote:
>> > Hi,
>> >
>> > When doing testing of NFSv3 loopback mounts (client and server are on
>> > the same IP address), I'm seeing a very reproducible hang in which the
>> > client stops receiving data from the server. The TCP connection is still
>> > marked as established, and the server appears to continue to receive and
>> > send data, however the client does not.
>> >
>> > So far, I've reproduced on both v4.0-rc1, and the Fedora v3.18.7 kernel.
>> >
>> > The reproducer is simply to loopback mount using NFSv3, and then run the
>> > 'fsx' filesystem exerciser. I'm usually able to trigger the hang with
>> > "fsx -N 100000 foobar".
>> >
>> > I've attached a couple of wireshark trace of a few frames just before
>> > and during the hang in case it jogs any memories.
>>
>> This bug appears to go away when I disable the splice()-based reads by
>> clearing the RQ_SPLICE_OK flag.
>>
>> I noticed that it always involved a combination of a READ and a
>> truncating SETATTR call. Are you sure that it is safe to share
>> pagecache pages directly with sendpage() in this way? As far as I can
>> tell, there is no locking to prevent them from being modified while in
>> the TCP send queue.
>
> This is the stable-pages problem that we've had forever, isn't it?  Or
> is this a different problem?

It is causing the TCP socket to hang, so it goes beyond the usual
stable pages issue.

-- 
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@...marydata.com
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html