Crash when sending a lot of messages through a unix socket

Wed May 2 16:31:51 EDT 2012

You mentioned your code is atomic. Are you certain that you can do a sock_sendmsg from a non process context? I believe you can't do that from a non process context cuz sock_sendmsg-->udp_sendmsg for DGRAM and i think that assumes you are in process context.

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From: kernelnewbies-bounces at kernelnewbies.org [kernelnewbies-bounces at kernelnewbies.org] On Behalf Of kernelnewbies-request at kernelnewbies.org [kernelnewbies-request at kernelnewbies.org]
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Today's Topics:

   1. please report distros with CONFIG_DYNAMIC_DEBUG, using
      ddebug_query=     boot param (Jim Cromie)
   2. Re: immutable wiki? (michi1 at michaelblizek.twilightparadox.com)
   3. Re: immutable wiki? (Bill Traynor)
   4. Crash when sending a lot of messages through a unix socket
      (Panagiotis Sakkos)

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Message: 1
Date: Tue, 1 May 2012 12:36:04 -0600
From: Jim Cromie <jim.cromie at gmail.com>
Subject: please report distros with CONFIG_DYNAMIC_DEBUG, using
        ddebug_query=   boot param
To: kernelnewbies <kernelnewbies at kernelnewbies.org>
Message-ID:
        <CAJfuBxw8aYimAU7kO42vh_e-zZBNSkw9Hd8Dx2tFCOWL4ueVgQ at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

hi all,

Ive been asked whether ddebug_query= boot param is used in any distros,
I think the question seeks to determine a good deprecation schedule for it
(its been obsoleted by dyndbg= in driver-core-next)

Would you all be so kind as to check your favorite distros, and report
the ones that
have one or both ?

Ubuntu 12.04 LTS lacks it:

jimc at chumly:~/projects/lx/linux-2.6$ grep DYNAMIC_DEBUG /boot/config*
/boot/config-3.0.0-17-generic:# CONFIG_DYNAMIC_DEBUG is not set
/boot/config-3.2.0-24-generic:# CONFIG_DYNAMIC_DEBUG is not set

Voyage linux also lacks it, (also debian based)

Fedora-16 has config option:

$ uname -a
Linux groucho.jimc.earth 3.3.2-6.fc16.x86_64 #1 SMP Sat Apr 21
12:43:20 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
$ grep DYNAMIC_DEBUG /boot/config-3.3.*
/boot/config-3.3.1-5.fc16.x86_64:CONFIG_DYNAMIC_DEBUG=y
/boot/config-3.3.2-1.fc16.x86_64:CONFIG_DYNAMIC_DEBUG=y
/boot/config-3.3.2-6.fc16.x86_64:CONFIG_DYNAMIC_DEBUG=y

but its not used by default. I have modified my grub defaults:

$ grep ddebug_query /etc/default/grub
GRUB_CMDLINE_LINUX='quiet rhgb loglevel=8 ddebug_query="module params
+p" dynamic_debug.verbose=1 nouveau.dyndbg nouveau.force_post=1
it87.dyndbg=+p nouveau.perflvl_wr=7777'

FYI, the above usage will eventually be unsupported,
it can be replaced in driver-core-next by either of:

  dyndbg="module params +p"
  params.dyndbg=+p
  params.dyndbg          # defaults to +p

the 2nd, 3rd forms also work for loadable modules (though params isnt
one of them)

thanks in advance
Jim

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Message: 2
Date: Wed, 2 May 2012 12:52:38 +0200
From: michi1 at michaelblizek.twilightparadox.com
Subject: Re: immutable wiki?
To: Bill Traynor <wmat at alphatroop.com>
Cc: kernelnewbies at kernelnewbies.org
Message-ID: <20120502105237.GA2229 at grml>
Content-Type: text/plain; charset=us-ascii

Hi!

On 09:29 Tue 01 May     , Bill Traynor wrote:
> I have an Editor account for the kernelnewbies.org wiki, but all pages
> are currently immutable.  Was the wiki made read-only at some point?

You must be on http://kernelnewbies.org/EditorsGroup to make changes. This
was made for spam procection. Everybody who is on the list can add you. What
is your username in the wiki?

        -Michi
--
programing a layer 3+4 network protocol for mesh networks
see http://michaelblizek.twilightparadox.com

------------------------------

Message: 3
Date: Wed, 2 May 2012 08:06:36 -0400
From: Bill Traynor <wmat at alphatroop.com>
Subject: Re: immutable wiki?
To: michi1 at michaelblizek.twilightparadox.com
Cc: kernelnewbies at kernelnewbies.org
Message-ID:
        <CAGfZjq69kO91rbiG8R5jTUmRDq3ZJRjp_oTLqS8wji1M=1NJ-Q at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

On Wed, May 2, 2012 at 6:52 AM,
<michi1 at michaelblizek.twilightparadox.com> wrote:
> Hi!
>
> On 09:29 Tue 01 May ? ? , Bill Traynor wrote:
>> I have an Editor account for the kernelnewbies.org wiki, but all pages
>> are currently immutable. ?Was the wiki made read-only at some point?
>
> You must be on http://kernelnewbies.org/EditorsGroup to make changes. This
> was made for spam procection. Everybody who is on the list can add you. What
> is your username in the wiki?

Thanks Michael, Rik already fixed it for me.

>
> ? ? ? ?-Michi
> --
> programing a layer 3+4 network protocol for mesh networks
> see http://michaelblizek.twilightparadox.com

------------------------------

Message: 4
Date: Wed, 2 May 2012 13:43:41 +0000
From: Panagiotis Sakkos <panos.sakkos at cern.ch>
Subject: Crash when sending a lot of messages through a unix socket
To: "kernelnewbies at kernelnewbies.org"
        <kernelnewbies at kernelnewbies.org>
Message-ID:
        <A1F86B12A2E22C4CB3164ECFFD1C54DB08EC9407 at PLOXCHG03.cern.ch>
Keywords: CERN SpamKiller Note: -50
Content-Type: text/plain; charset="iso-8859-1"

Hi,

I am trying to log information from within the kernel with the use of a unix socket (/dev/log).
My code is a kprobe handler, so while executing I am atomic and uninterrupted.
The crashes begin when I do stress tests against my module, so i.e. more than 50 logs per second.
The crash messages I get every time are different (from NULL reference, unable to handle page request etc), so I suppose that something is overwritten and this leads to the crash.

I don't want to post the code here because it ~100 LOC but these are my steps:

Initialization:
       call sock_create_kern, with PF_UNIX, SOCK_DGRAM, 0 and the address of my socket,
       then I memset to 0 my sockaddr_un variable and then I set its sun_family to PF_UNIX and copy the "/dev/log" string to sun_path

Logging:
    I have the message that I want to log in variable called buffer and its length in variable called message_length,
    I set the msg_name of the msghdr to the address of my sockaddr_un variable, than the msn_namelen to sizeof(sockadrr_un), the msg_iov to an iovec variable which contains the buffer and the message_length values, msg_iovlen to 1 and msg_control, msg_controllen to 0.
    Then I set the fs to KERNEL_DS, call sock_sendmsg with parameters my socket, the address of my msghdr and the message_length and then I restore the fs that there was before setting it to KERNEL_DS.

Please note that my socket, sockadd_un and my buffer are static variables. Also I always use the socket which is initialized once in the Initialization state (function).

Do you see any "bad practice" or something that could lead to crashes when stressing with a lot of messages the socket?

Thank you in advance!
Panos
--
http://www.cern.ch/psakkos
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