[Devel] Re: c/r of pdeath

[Serge E. Hallyn]

Quoting Oren Laadan (orenl at cs.columbia.edu):
> 
> 
> Serge E. Hallyn wrote:
> > Hi Oren,
> > 
> > commit 9a45e26c0aabda6a94e2ac620befd8ee12a7363d adds
> > reset of pdeath_signal.  It does so unconditionally.  I
> > don't think that's safe.  Perhaps if pdeath_signal is
> > anything other than 0, it should only be restored if
> > the task is capable(CAP_KILL)?
> 
> Hmmm... maybe I'm missing something here, but --

Nope, you're not.  I was thinking wrong.

> pdeath_signal indicates that the process wishes to receive
> a signal, not to send one. It may change through prctl()
> without requiring any capabilities from the caller. Finally
> it is reset at fork/clone.
> 
> So at worse it will kill the specific task that holds it ?
> 
> --
> 
> As a side note - for a brief moment I worried that it may
> break restart with zombies, if the to-be-zombie process has
> a child that already restarted (including pdeath_signal) and
> then exits, then the child will receive a signal unwillingly.
> 
> I then realized that it's safe as long as we restore parents
> before their children. In turn this depends on the checkpoint
> order, which indeed operates this way.
> 
> Otherwise we would have needed set this to all processes
> after all zombies indeed have terminated - which means another
> sync point at restart, or a sweep by coordinator on all tasks.
> 
> Oren.
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