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Date:	Tue, 21 Oct 2008 00:48:16 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	"Dâniel Fraga" <fragabr@...il.com>
cc:	Thomas Gleixner <tglx@...utronix.de>,
	David Miller <davem@...emloft.net>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] tcp FRTO: in-order-only "TCP proxy" fragility workaround
 (fwd)

On Fri, 17 Oct 2008, Dâniel Fraga wrote:

> On Mon, 13 Oct 2008 16:35:08 +0300 (EEST)
> "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi> wrote:
> 
> 	Just reporting another stall event... Who knows it helps in some way...
> 
> > ...might turn out related. It has somewhat similar problem though 
> > different syscall. Not enough info on what kernel version etc. 
> > there though.
> 
> 	Well, I can be wrong, but I think those stalls are related to USB (or USB helped to 
> "solve" the stall temporarily)... I explain below (I have a monitor with usb hub connected):
> 
> Oct 17 19:35:55 tux sudo: pam_unix(sudo:session): session opened for user root by fraga(uid=0)
> Oct 17 19:35:55 tux sudo: pam_unix(sudo:session): session closed for user root
> 
> 	^---------- sudo opened the session at 19:35
> 
> Oct 17 19:38:16 tux sudo:    fraga : TTY=pts/2 ; PWD=/usr/local/lib ; USER=root ; COMMAND=/usr/local/bin/rm libdvdread.a libdvdread.la libdvdread.so libdvdread.so.3 libdvdread.so.3.2.1 libdvdread.so.4 libdvdread
> .so.4.1.2
> 
> 	^---------- I tried to run this command with sudo. And it stalled. Notice that it was logged only on 19:38.
> 
> Oct 17 19:38:16 tux sudo: pam_unix(sudo:session): session opened for user root by fraga(uid=0)
> Oct 17 19:38:16 tux sudo: pam_unix(sudo:session): session closed for user root
> Oct 17 19:40:20 tux vmunix: ci000/000:21ub/-/-./-../-..:./nu/nu7
> 
> 	^----------- Here is the stall. You can see that the log is corrupted, every other line.
> 
> Oct 17 19:40:20 tux vmunix: 6ipt S I 11 os Lgtc pia S os]o s-000:21112
> 
> 	^----------- Every other line. Here is when I turned off my monitor with USB... Unless it was an extreme coincidence, I'm sure this event
> of turning off and...

You probably meant every other character... :-) The same as with the 
netfilter logs... I've two open question related to it, where did the 
every other letter go...? and why not a larger block but only a single 
char is missing (at a time)? I've no idea about printk's internals, maybe 
I'll try to ping somebody tomorrow about it.

> Oct 17 19:40:25 tux vmunix: sd 9:0:0:0: [sdb] Attached SCSI removable disk
> Oct 17 19:40:25 tux scsi.agent[5498]: disk at /devices/pci0000:00/0000:00:02.1/usb2/2-1/2-1.1/2-1.1.1/2-1.1.1:1.0/host9/target9:0:0/9:0:0:0
> 
> 	^---------- ...turning on again, helped to "solve" the stall. The stall ended when I turned off the monitor.
> 
> Oct 17 19:40:28 tux sudo:    fraga : TTY=pts/2 ; PWD=/usr/local/lib ; USER=root ; COMMAND=/usr/local/bin/ls
> Oct 17 19:40:28 tux sudo: pam_unix(sudo:session): session opened for user root by fraga(uid=0)
> Oct 17 19:40:28 tux sudo: pam_unix(sudo:session): session closed for user root
> Oct 17 19:40:30 tux scsi.agent[5310]: Attribute /sys/devices/pci0000:00/0000:00:02.1/usb2/2-1/2-1.1/2-1.1.1/2-1.1.1:1.0/host9/type does not exist
> Oct 17 19:40:35 tux scsi.agent[5493]: Attribute /sys/devices/pci0000:00/0000:00:02.1/usb2/2-1/2-1.1/2-1.1.1/2-1.1.1:1.0/host9/target9:0:0/type does not exist
> Oct 17 20:12:37 tux vmunix: usb-storage: device found at 14
> Oct 17 20:12:37 tux vmunix: usb-storage: waiting for device to settle before scanning
> Oct 17 20:12:42 tux vmunix: scsi 10:0:0:0: Direct-Access     Generic  ls SC   53 Q  NI 
> Oct 17 20:12:42 tux vmunix: k
> Oct 17 20:12:42 tux scsi.agent[7439]: disk at /devices/pci0000:00/0000:00:02.1/usb2/2-1/2-1.1/2-1.1.1/2-1.1.1:1.0/host10/target10:0:0/10:0:0:0
> Oct 17 20:12:47 tux vmunix: DROP INPUT: IN=eth0 OUT= MAC=ff:ff:ff:ff:ff:ff:00:15:e9:e2:00:db:08:00 SRC=192.168.0.1 DST=255.255.255.255 LEN=334 TOS=0x00 PREC=0x00 TTL=64 ID=6668 PROTO=UDP SPT=67 DPT=68 LEN=314 
> Oct 17 20:12:47 tux scsi.agent[7252]: Attribute /sys/devices/pci0000:00/0000:00:02.1/usb2/2-1/2-1.1/2-1.1.1/2-1.1.1:1.0/host10/type does not exist
> Oct 17 20:12:53 tux scsi.agent[7435]: Attribute /sys/devices/pci0000:00/0000:00:02.1/usb2/2-1/2-1.1/2-1.1.1/2-1.1.1:1.0/host10/target10:0:0/type does not exist
> 
> 	***
> 	
> 	At the server I have an usb device connected too...
> 
> 	OR at eh end it's just a symptom of the problem... I don't
> know. The interesting thing is that as soon as I turned off the monitor 
> (at the exact moment), the speaker beeped, because I used TAB to auto
> complete my command, and I knew that sudo wasn't stalled
> anymore.
> 
> 	Maybe what the kernel does when we remove a usb hub could give us a hint about the stalling issue...

I doubt we'll find the cause from networking...

Trying something a bit more generic:

Try running vmstat 1 > somelog.file to see if there's something 
particularly interesting behavior during the stall.

-- 
 i.

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