Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH -mm] swsusp: freeze user space processes first | Date | Sun, 5 Feb 2006 14:34:40 +0100 |
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On Sunday 05 February 2006 12:39, Rafael J. Wysocki wrote: > On Sunday 05 February 2006 12:18, Pavel Machek wrote: > > 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@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. > > > > Can you produce userland testcase? If we have uninterruptible process for > > days... that's a bug in kernel, suspend or not. > > Sure, no problem. [Pretty scary, no?]
Actually it's not that bad, because the parent will be killable when the child exit()s (or gets killed).
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