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

[Pavel Machek]

On Ne 05-02-06 12:11:06, Rafael J. Wysocki wrote:
> On Sunday 05 February 2006 11:50, Ingo Molnar wrote:
> > 
> > * Rafael J. Wysocki <rjw@xxxxxxx> 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.

Can you produce userland testcase? If we have uninterruptible process for
days... that's a bug in kernel, suspend or not.
								Pavel
-- 
Thanks, Sharp!
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