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Re: Broken readdir() since 3.5 for ext3 on mips-n32

To: linux-mips@linux-mips.org
Subject: Re: Broken readdir() since 3.5 for ext3 on mips-n32
From: Lluís Batlle i Rossell <viric@viric.name>
Date: Mon, 5 Nov 2012 22:20:19 +0100
In-reply-to: <20121105073221.GG2052@vicerveza.homeunix.net>
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Hello,

with the help of Lars on irc, we've tracked down the issue to a broken readdir()
in ext3 in n32, introduced in the kernel 3.5 by this commit:
d7dab39b6e16d5eea78ed3c705d2a2d0772b4f06

That renders ext3 quite useless in mips n32.

In a kernel after that commit, the example program in the 'getdents' man page
returns this:
[root@fu2:~/readdir]# ./getdents 
--------------- nread=116 ---------------
i-node#  file type  d_reclen  d_off   d_name
    3694  regular      20 1780583312  prova.c
 1037850  regular      24 -985956880  getdents.c
 1037848  directory    16 -1999547753  .
 1037849  regular      20  222381689  getdents
  778241  directory    16 -1849228342  ..
    3647  regular      20         -1  prova


I took Lars suggestion of applying the patch I attach (forcing ext3 to think it
is a 32-bit system), and then all works. init (upstart) doesn't deadlock 
anymore, readdir() works fine, and the getdents info looks right:
[root@fu2:~/readdir]# ./getdents 
--------------- nread=116 ---------------
i-node#  file type  d_reclen  d_off   d_name
    3694  regular      20  334739480  prova.c
 1037850  regular      24  473707228  getdents.c
 1037848  directory    16  824759881  .
 1037849  regular      20  875064456  getdents
  778241  directory    16 1524836457  ..
    3647  regular      20 2147483647  prova

How to solve this, I don't know. But it seems that ext3 thinks that mips-n32
programs can eat some 64-bit words in d_off.

Regards,
Lluís.

On Mon, Nov 05, 2012 at 08:32:21AM +0100, Lluís Batlle i Rossell wrote:
> This same issue below happens to me in 3.5.7 too. So, the change is somewhere
> between 3.4 and 3.5.
> 
> Regards,
> Lluís.
> 
> On Mon, Nov 05, 2012 at 12:21:19AM +0100, Lluís Batlle i Rossell wrote:
> > I've investigated better the issue.
> > 
> > I found that, in 3.4 vs 3.6.4, the behaviour that changed is that of 
> > readdir().
> > 
> > Using the same userland binaries, I've run a little program in both kernels:
> > -------- prova.c
> > #include <sys/types.h>
> > #include <dirent.h>
> > 
> > int main() {
> >         DIR *d = opendir("/etc/init");
> > 
> >         if (d == NULL) {
> >                 fprintf(stderr, "d NULL\n");
> >                 return -1;
> >         }
> > 
> >         struct dirent *ent;
> >         ent = readdir(d);
> > 
> >         if (ent == NULL) {
> >                 fprintf(stderr, "ent NULL\n");
> >                 return -1;
> >         }
> > }
> > -----------
> > 
> > 
> > This program does not print anything on 3.4, but on 3.6, it prints "ent 
> > NULL".
> > 
> > In both cases, /etc/init is full of symlinks, like this (from a script 
> > session
> > in 3.6.4):
> > -------
> > S'ha iniciat l'execució de script a dl 05 nov 2012 00:16:53 CET
> > sh-4.2# ./prova
> > ent NULL
> > sh-4.2# ls -ld /etc/init
> > drwxr-xr-x 2 root root 4096  5 nov 00:12 /etc/init
> > sh-4.2# ls -l /etc/init
> > total 0
> > lrwxrwxrwx 1 root root 25  5 nov 00:12 atd.conf -> /etc/static/init/atd.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 boot.conf -> 
> > /etc/static/init/boot.conf
> > lrwxrwxrwx 1 root root 40  5 nov 00:12 control-alt-delete.conf -> 
> > /etc/static/init/control-alt-delete.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 cron.conf -> 
> > /etc/static/init/cron.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 dbus.conf -> 
> > /etc/static/init/dbus.conf
> > lrwxrwxrwx 1 root root 28  5 nov 00:12 dhcpcd.conf -> 
> > /etc/static/init/dhcpcd.conf
> > lrwxrwxrwx 1 root root 37  5 nov 00:12 emergency-shell.conf -> 
> > /etc/static/init/emergency-shell.conf
> > lrwxrwxrwx 1 root root 37  5 nov 00:12 invalidate-nscd.conf -> 
> > /etc/static/init/invalidate-nscd.conf
> > lrwxrwxrwx 1 root root 25  5 nov 00:12 kbd.conf -> /etc/static/init/kbd.conf
> > lrwxrwxrwx 1 root root 27  5 nov 00:12 klogd.conf -> 
> > /etc/static/init/klogd.conf
> > lrwxrwxrwx 1 root root 25  5 nov 00:12 lvm.conf -> /etc/static/init/lvm.conf
> > lrwxrwxrwx 1 root root 30  5 nov 00:12 mountall.conf -> 
> > /etc/static/init/mountall.conf
> > lrwxrwxrwx 1 root root 36  5 nov 00:12 mountall-ip-up.conf -> 
> > /etc/static/init/mountall-ip-up.conf
> > lrwxrwxrwx 1 root root 34  5 nov 00:12 mount-failed.conf -> 
> > /etc/static/init/mount-failed.conf
> > lrwxrwxrwx 1 root root 32  5 nov 00:12 networking.conf -> 
> > /etc/static/init/networking.conf
> > lrwxrwxrwx 1 root root 40  5 nov 00:12 network-interfaces.conf -> 
> > /etc/static/init/network-interfaces.conf
> > lrwxrwxrwx 1 root root 32  5 nov 00:12 nix-daemon.conf -> 
> > /etc/static/init/nix-daemon.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 nscd.conf -> 
> > /etc/static/init/nscd.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 ntpd.conf -> 
> > /etc/static/init/ntpd.conf
> > lrwxrwxrwx 1 root root 30  5 nov 00:12 runlevel.conf -> 
> > /etc/static/init/runlevel.conf
> > lrwxrwxrwx 1 root root 30  5 nov 00:12 shutdown.conf -> 
> > /etc/static/init/shutdown.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 sshd.conf -> 
> > /etc/static/init/sshd.conf
> > lrwxrwxrwx 1 root root 29  5 nov 00:12 syslogd.conf -> 
> > /etc/static/init/syslogd.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 tty1.conf -> 
> > /etc/static/init/tty1.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 tty2.conf -> 
> > /etc/static/init/tty2.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 tty3.conf -> 
> > /etc/static/init/tty3.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 tty4.conf -> 
> > /etc/static/init/tty4.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 tty5.conf -> 
> > /etc/static/init/tty5.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 tty6.conf -> 
> > /etc/static/init/tty6.conf
> > lrwxrwxrwx 1 root root 26  5 nov 00:12 udev.conf -> 
> > /etc/static/init/udev.conf
> > lrwxrwxrwx 1 root root 33  5 nov 00:12 udevtrigger.conf -> 
> > /etc/static/init/udevtrigger.conf
> > sh-4.2# exit
> > 
> > S'ha finalitzat l'execució de script a dl 05 nov 2012 00:17:22 CET
> > --------
> > 
> > 
> > 
> > 
> > On Fri, Nov 02, 2012 at 07:38:28PM +0100, Lluís Batlle i Rossell wrote:
> > > Hello,
> > > 
> > > updating my kernel from 3.4.2 to 3.6.4, I've noticed that upstart 
> > > deadlocks at
> > > the very start. Stracing, I think it has to do with INOTIFY, because it
> > > deadlocks very early and little more has been done then.
> > > 
> > > Going 'back' to 3.4.16, makes upstart work fine. I've not tested middle 
> > > kernels.
> > > 
> > > I've seen this only on the fuloong minipc (mips n64), but I've done 
> > > similar
> > > steps with the same distributions on armv5tel, i686 and x86_64, and there 
> > > all
> > > works fine.
> > > 
> > > Does anybody know of anything broken around inotify, between 3.4 and 3.6 
> > > linux
> > > mips?
> > > 
> > > Any suggestion on what kernel change could have related to this, and so, 
> > > get a
> > > clue about what middle version to test?
> > > 
> > > Regards,
> > > Lluís.

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