Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH -mm] swsusp: freeze user space processes first | Date | Sun, 5 Feb 2006 12:11:06 +0100 |
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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.
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