Re: [PATCH -mm] swsusp: freeze user space processes first

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Sunday 05 February 2006 11:50, Ingo Molnar wrote:
> 
> * Rafael J. Wysocki <rjw@sisk.pl> wrote:
> 
> > > The logic in that loop makes my brain burst.
> > > 
> > > What happens if a process does vfork();sleep(100000000)?
> > 
> > The freezing of processes will fail due to the timeout.
> > 
> > Without the if (!p->vfork_done) it would fail too, because the child 
> > would be frozen and the parent would wait for the vfork completion in 
> > the TASK_UNINTERRUPTIBLE state (ie. unfreezeable).  But in that case 
> > we have a race between the "freezer" and the child process (ie. if the 
> > child gets frozen before it completes the vfork completion, the paret 
> > will be unfreezeable) which sometimes leads to a failure when it 
> > should not.  [We have a test case showing this.]
> 
> then i'd suggest to change the vfork implementation to make this code 
> freezable.

I think you are right, but I don't know how to do this.

> Nothing that userspace does should cause freezing to fail.   If it does,
> we've designed things incorrectly on the kernel side. 

I tend to agree.

Generally, the problem is due to the use of completions where userland
processes are waited for.  The two places I know of are the vfork
implementation and the usermode helper code.

Greetings,
Rafael
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