From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sc8-sf-mx2-b.sourceforge.net ([10.3.1.12] helo=sc8-sf-mx2.sourceforge.net) by sc8-sf-list1.sourceforge.net with esmtp (Cipher TLSv1:DES-CBC3-SHA:168) (Exim 3.31-VA-mm2 #1 (Debian)) id 1APXDZ-0006ft-00 for ; Thu, 27 Nov 2003 17:14:45 -0800 Received: from pop.gmx.net ([213.165.64.20] helo=mail.gmx.net) by sc8-sf-mx2.sourceforge.net with smtp (Exim 4.24) id 1APXDY-0002gK-GI for user-mode-linux-devel@lists.sourceforge.net; Thu, 27 Nov 2003 17:14:44 -0800 Message-ID: <010c01c3b54d$99552830$2000000a@schlepptopp> From: "roland" References: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Subject: [uml-devel] bug in COW? - Re: [uml-user] uml 2.6.0-test9 crash Sender: user-mode-linux-devel-admin@lists.sourceforge.net Errors-To: user-mode-linux-devel-admin@lists.sourceforge.net List-Help: List-Post: List-Subscribe: , List-Id: The user-mode Linux development list List-Unsubscribe: , List-Archive: Date: Fri, 28 Nov 2003 02:18:57 +0100 Content-Transfer-Encoding: quoted-printable To: Henrik Nordstrom , Sven 'Darkman' Michels Cc: user-mode-linux-devel@lists.sourceforge.net, uml-user Hi! I made some further investigation. i forgot to mention, that i`m using reiserfs and also use the copy-on-write= (cow) feature, uml has. the system-freeze i experience seems to have to do with c= opy-on-write. as a test, i made a copy of my rootfs, made it available under /dev/ubd/2 i= nside the uml and mounted that under /mnt. i did an extra fsck before - no inconsiste= ncy was reported. then i did some stresstests again - worked fine! after making the rootfs-clone a cow-filesystem (by adding ubd2=3Drootfsclon= e.cow,rootfsclone.img), the freeze happened again when doing some heavy writing. so - am i allowed = to assume, that there is a bug in the copy-on-write code? btw: could anybody recommend a general filesystem stresstest-tool which doe= s the worst to filesytems, you can do (besides formatting or overwriting)? :D it seems, that this bug happens under certain circumstances only. if i "dd= " to an empty filesystem, it doesn`t seem to freeze the uml at once. but it happend again after a whi= le, when i did some additionial copying of directory-trees while dd`=ECng to disk in the backgr= ound. regards roland ps: accidentally, i opened a cow-file with vi - and i saw that the path to the = original readonly filesystem image seems to be stored with full path information. would that = mean: if i want to relocate the fs-image with it`s accociated cow-file, i`m out of luck? is th= ere any reason why there are absolute, not relative paths inside? pps: > > The UML did the frist two dd's without problems, then it started to > > hang.. i checked outside and saw the process switching states from > > R to D and then back to R... so after a few secs the dd's did all > > succeed and the uml is still running. So it didn't crash or so > > but it also didn't play very well with that. > > Sounds as if it started to get blocked by disk I/O on the host.. ubd > device I/O is a latency killer for UML as a blocking disk I/O operation > will block the whole UML kernel until the host finishes. yes - i think what hendrik says is right! this is just normal behaviour. th= e first 2 dd`s ran without "problems" because the host just cached that i/o`s. then it beg= an writing to disk and this may have caused some delay you recognized as a "hang". in general = - i/o scheduling of 2.4.x kernels is not the very best. 2.6 kernel series has new i/o schedulers whic= h are improved a LOT! ----- Original Message -----=20 From: "Henrik Nordstrom" To: "Sven 'Darkman' Michels" Cc: Sent: Friday, November 28, 2003 12:50 AM Subject: Re: [uml-devel] Re: [uml-user] uml 2.6.0-test9 crash > On Thu, 27 Nov 2003, Sven 'Darkman' Michels wrote: > > > The UML did the frist two dd's without problems, then it started to > > hang.. i checked outside and saw the process switching states from > > R to D and then back to R... so after a few secs the dd's did all > > succeed and the uml is still running. So it didn't crash or so > > but it also didn't play very well with that. > > Sounds as if it started to get blocked by disk I/O on the host.. ubd > device I/O is a latency killer for UML as a blocking disk I/O operation > will block the whole UML kernel until the host finishes. > > > BTW: did you had any problems with building an uml kernel on 9.0? > > I have no problem with building UML on RH9, but I have a memory of some > singnal trick which was needed at some point.. Make sure the UML is up to > date. > > Regards > Henrik > hi !=B4 i think , i`m able to crash my uml. :( i did some stress-testing with my uml-2.6.0-test9 on 2.6.0-test9-skas host = and i unfortunately seem able to crash it very easily. this was the way i recognized it: first i executed while true;do find /;done >/dev/zero & several times and all worked well. watched that with "top" inside the uml and found dozens of "finds" sharing = the cpu as expected(spending most of their time on system calls indeed). on host, cpu usage of uml went to ~99% - all fine so far. then i thought: mhhhh - ok - eat THIS: while true;do dd if=3D/dev/zero of=3Dtest.dat bs=3D1k count=3D10000;done & after executing this, my uml got stuck. no output, no response to input - e= ven a ping to the uml didn`t=B4give back a sign of life. the uml didn`t crash or = panic - it just gets stuck and unresponsive - uml process remains at 99% on the host. at a second, third, fourth try, i isolated the problem a little bit: one or two non looped "dd if=3D/dev/zero of=3Dtest.dat bs=3D1k count=3D1000= 0" just are enough to produce the same result.(under 2.6.0test9-skas-host and ALSO under 2.4.2= 2-99-default suse9 host, rootfs inside uml is suse9) is anybody able to reproduce this? if so - what do do further for analyzing? i could make the uml downloadable and could send some output from strace (i= f i attach strace to the remaining "99% cpu hog", it exits very quickly with a SIGALARM) maybe an uml bug or even an issue for lkml? regards roland ------------------------------------------------------- This SF.net email is sponsored by: SF.net Giveback Program. 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