[Devel] Re: bugs with ckpt-v15-dev

[Serge E. Hallyn]

Quoting Nathan Lynch (ntl at pobox.com):
> "Serge E. Hallyn" <serue at us.ibm.com> writes:
> 
> > Quoting Nathan Lynch (ntl at pobox.com):
> >> Last commit is ed3b275 "allow error string during checkpoint while
> >> holding a spinlock".
> >> 
> >> # bash -c 'exec <&- >&- 2>&- ; while : ; do : ; done' &
> >> [1] 2269
> >> # ckpt $! > /tmp/bash.ckpt
> >> 
> >> BUG: sleeping function called from invalid context at mm/slub.c:1595
> >
> > Yeah, not only does ckpt_write_err() get called under task_lock, but
> > the fn returns without ver doing put_task_struct.  (I'd generate and
> > send the quick trivial patch, but my git tree is in a bit of a debugme
> > state right now)
> 
> Would prefer to just rip that thing out, it's cost me more trouble then
> it's worth.

Which thing - CHECKPOINT_SUBTREE, freezer check, or ckpt_write_err?

> > Now mind you this shows that your ckpt program isn't sending
> > CHECKPOINT_SUBTREE with flags.
> 
> I don't follow.  There is "user error" here in that I'm not freezing the
> task before checkpointing[1], but my ckpt command is passing the subtree
> flag (0x4) afaict:
> 
> SYS_335(0x9ec, 0x1, 0x4, 0xbfdc6200, 0[2542:c/r:may_checkpoint_task] check 2540

Oh, it's the freezer test in may_checkpoint_task you're getting the
error on?  (in my git tree I'd commented that one out temporarily so I
just assumed it was the subtree check in get_container :)

> > This in turns means you are probably
> > not using the ckpt-v15-dev version of user-cr, and if that is
> > the case it makes your problems with gconf shared file mapping more
> > suspect ask well...?
> 
> After updating to the latest user-cr I get the same BUGs.
> 
> [1] Should CONFIG_CHECKPOINT depend on CONFIG_CGROUPS and/or
> CONFIG_CGROUPS_FREEZER?  We require tasks to be put in frozen state
> before checkpoint, is there any mechanism apart from
> cgroup/freezer.state to do this?

A task can self-checkpoint without the freezer though.

-serge
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