[Unionfs] Re: 2.6.26-rc4: smack and unionfs deadlock

[Casey Schaufler]

Luiz Fernando N. Capitulino wrote:
>  Hi Casey,
>
>  I've got another deadlock which only happens when CONFIG_SMACK is
> enabled, but this time it happens with unionfs and I don't know
> which of the two is causing the problem.
>
>  If you mount a unionfs stack and try a ls on it, ls will hang
> and you'll get a deadlock.
>
>  For example:
>
> """
> # mount -t unionfs -odirs=x=rw:drakx=ro unionfs Pictures
> # ls -la Pictures/
> """
>
>  The directories names don't matter, but for what is worth,
> x and drakx have some files and Picture is empty.
>
>  To duplicate this problem you will need:
>
> 1. kernel version 2.6.26-rc4
>
> 2. Unionfs latest patch:
>
> http://download.filesystems.org/unionfs/unionfs-2.x/unionfs-2.3.3_for_2.6.25.diff.gz
>
> 3. fs-unionfs-use-new-umount_begin-prototype.patch (attached)
>
> 4. Casey's fix for mount hang, otherwise you will get the mount
> deadlock bug with unionfs (smack-fuse-mount-hang-fix.patch, attached)
>
>  Then try to mount a unionfs stack, I'm pretty sure any populated
> stack will cause the problem.
>
>  By the way, I've also attached the lockdep warning for this
> and the sysrq+w output.
>
>  Please, let me know if you need any other information.
>
>  Best regards.
>
>   

GGSC. Ok, I'm looking into it. I'll let you know what I find.
Thank you.

-- 

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

Casey Schaufler
casey at schaufler-ca.com
650.906.1780