Messages in this thread | | | Date | Tue, 2 Dec 2008 12:51:30 -0800 | From | Sukadev Bhattiprolu <> | Subject | Re: [RFC][PATCH 4/5] Protect cinit from fatal signals |
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First of, thanks for taking the time to review/comment.
Bastian Blank [bastian@waldi.eu.org] wrote: | On Mon, Dec 01, 2008 at 12:21:12PM -0800, Sukadev Bhattiprolu wrote: | > Container-inits are special in some ways and this change requires SIGKILL | > to terminate them. | | No. They have are not special from the outside namespace.
I agree that they should not be. But they are special today in at least one respect - terminating a container-init will terminate all processes in the container even those that are in unrelated process groups.
Secondly, a poorly written container-inits can take the entire container down, So we expect that container-inits to handle/ignore all signals rather than SIG_DFL them. Current global inits do that today and container-inits should too. It does not look like an unreasonable requirement.
If container-inits do not properly handle signals, it is appearing that we need to make a trade-off in terms of semantics/complexity. See following URL for the history.
https://lists.linux-foundation.org/pipermail/containers/2008-November/013991.html
So the basic requirements are:
- container-init receives/processes all signals from ancestor namespace. - container-init ignores fatal signals from own namespace.
We are simplifying the first to say that:
- parent-ns must have a way to terminate container-init - cinit will ignore SIG_DFL signals that may terminate cinit even if they come from parent ns
| | Also it was discussed to use pid namespaces to preserve the local pid of | a process during snapshot/restore. This means that every process may get | the state of a container-init. And then it is not longer a wise idea to | make them behave different from the outside.
The one change in the state of the process I see is if someone relies on following fields from /proc/<pid>/status
SigPnd: 0000000000000000 ShdPnd: 0000000000000000 SigBlk: 0000000000000000 SigIgn: 0000000000000000 SigCgt: 0000000000000000
to decide if they can send, say SIGUSR1, to terminate the process. If they do, they maybe in for a surprise. But if the container-init properly handles/ignores signals, this info will be consistent.
Yes its not ideal and yes, the semantic change described above is a trade-off. We are trying to find out if this change is unreasonable or will break something really bad way.
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