Re: 2.6.33-rc8 breaks UML with Restrict initial stack space expansion to rlimit

[KOSAKI Motohiro]

> 
> 
> In message <20100214164023.GA2726@xxxxxxxxx> you wrote:
> > It looks like the commit 803bf5ec259941936262d10ecc84511b76a20921
> > (fs/exec.c: restrict initial stack space expansion to rlimit) broke my
> > user mode Linux setup by somehow preventing system setup from running
> > properly (or killing some processes that try to mount things, etc.).
> > This commit turned up as the reason based on git bisect and reverting it
> > fixes my UML test setup (Ubuntu 9.10 on both host and in UML and AMD64
> > arch for both). I have no idea what exactly would be the main cause for
> > this issue, but this looks like a somewhat unfortunately timed
> > regression in 2.6.33-rc8.
> > 
> > The failed run shows like this (with current linux-2.6.git):
> > 
> > ...
> > EXT3-fs (ubda): mounted filesystem with writeback data mode
> > VFS: Mounted root (ext3 filesystem) readonly on device 98:0.
> > IRQ 3/console-write: IRQF_DISABLED is not guaranteed on shared IRQs
> > IRQ 2/console: IRQF_DISABLED is not guaranteed on shared IRQs
> > IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs
> > IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs
> > mountall: mount /sys/kernel/debug [218] killed by KILL signal
> > mountall: Filesystem could not be mounted: /sys/kernel/debug
> > mountall: mount /dev [219] killed by KILL signal
> > mountall: Filesystem could not be mounted: /dev
> > mountall: mount /tmp [220] killed by KILL signal
> > mountall: Filesystem could not be mounted: /tmp
> > mountall: mount /var/lock [222] killed by KILL signal
> > mountall: Filesystem could not be mounted: /var/lock
> > ...

Wow. It seems very strange. Usually stack overflow makes SIGSEGV, not SIGKILL.
plus, In my environment (x86_64 non-uml), mount command doesn't use
the stack so much.


% /usr/bin/time --format="mem %M" ls
/usr/bin/time --format="mem %M" ls
GPATH      INSTALL  README       configure    fdisk          lib      misc-utils   schedutils
mem 3232

% sudo /usr/bin/time --format="mem %M"  mount -a
sudo /usr/bin/time --format="mem %M"  mount -a
mem 2992


Hmmm...
I have no idea.



> > 
> > 
> > With 803bf5ec reverted, UML comes up and the output looks like this:
> > 
> > ...
> > EXT3-fs (ubda): mounted filesystem with writeback data mode
> > VFS: Mounted root (ext3 filesystem) readonly on device 98:0.
> > IRQ 3/console-write: IRQF_DISABLED is not guaranteed on shared IRQs
> > IRQ 2/console: IRQF_DISABLED is not guaranteed on shared IRQs
> > IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs
> > IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs
> > init: procps main process (226) terminated with status 255
> > fsck from util-linux-ng 2.16
> > ...
> 
> Crud, the "killed" is definitely something this patch could cause.
> 
> I'm not familiar with UML.  Is this the guest and the host booting rc8,
> or just the host?  Does UML use stack protection at all?
> 
> Can you try booting the guest to init=/bin/sh and try running some tests
> to see what you can set 'ulimit -s' to and still be able to run a simple
> command like '/bin/ls'?
> 
> Mikey
> 
> > 
> > -- 
> > Jouni Malinen                                            PGP id EFC895FA
> > 
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