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

[Luiz Fernando N. Capitulino]

Em Sat, 07 Jun 2008 14:47:04 -0700
Casey Schaufler <casey at schaufler-ca.com> escreveu:

| Luiz Fernando N. Capitulino wrote:
| > Em Thu, 05 Jun 2008 22:11:19 -0700
| > Casey Schaufler <casey at schaufler-ca.com> escreveu:
| >
| > | Casey Schaufler wrote:
| > | > 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.
| > | >>
| > | >>   
| > | >
| > | > I need a little education. unionfs has a lock on its superblock,
| > | > which appears to be where we're getting hung up. What condition
| > | > is this lock for? It would seem that a getxattr would be pretty
| > | > safe without having the superblock locked, but no one is going
| > | > to accuse me of being excessively skilled at locking issues.
| > | > I'm going to see what goes wrong without that lock, and if removing
| > | > it takes care of the problem. There may be more than one dragon
| > | > in these waters.
| > | >
| > | > Thank you.
| > | >
| > | OK. The sb associated with unionfs has a magic number of 0,
| > | which implies you haven't set it. Is this intentional, or
| > | do you just figure no one cares, or should care?
| > | 
| > | I can relieve the hang by having the Smack code treat
| > | unionfs (actually the "0" file system) as one of the
| > | special cases. The "real" file shows the correct smack
| > | value, the unionfs shows "*", and access is correctly
| > | controlled in either case. I'm still looking to see what
| > | to do better, and I'd still like to understand the locking
| > | strategy better.
| >
| >  Casey, I'm afraid that only Erez (unionfs maintainer)
| > can answer you here but it seems that he's away or
| > something.
| >
| >  His last message on unionfs ML dates about one month
| > back.
| >
| >  :(
| Ok. Here's a temporary patch that makes everything except looking at
| the Smack label work properly. I haven't signed it off because I
| don't think it's ready for prime-time, but if the problem is holding
| anyone up it will allow them to proceed.

 Passed basic tests.

 Does the problem with the Smack label only happen for unionfs
mounts?

 Thank you very much, Casey.

-- 
Luiz Fernando N. Capitulino