[Devel] Re: [PATCH 1/3] Signal semantics for /sbin/init

[sukadev at us.ibm.com]

| > | > One solution I was thinking of was to possibly queue pending blocked
| > | > signals to a container init seperately and then requeue them on the
| > | > normal queue when signals are unblocked. Its definitely not an easier
| > | > solution, but might be less intrusive than the "signal from parent ns
| > | > flag" solution.

Hmm.  Stumbled upon an issue while coding this up.

For real time signals, is the order in which signals are delivered
important ? If so, the above solution won't work, because when requeing
signals from pid namespace to the task, we may lose the order of signals.

i.e:
	- signal sig1 is blocked.

	- sig1 is posted and queued on the ns->cinit_blocked_pending queue

	- just as we enter sigprocmask() to unblock sig1, if sig2 is
	  posted, we queue sig2 on task->pending queue since sig2 is not
	  blocked.

	- when we actually unblock sig1, if we requeue ns->cinit_blocked_pending
	  signals (i.e sig1) after sig2 we end up reversing the order of the
	  signals sig1 and sig2.

	  if we requeue the ns-> signals before sig2 and another sig1
	  was received after the sig2 and just before the unblock, we
	  again lose the order.

The order of signals is not important to legacy signals (< SIGRTMIN) but is 
probably an issue for signals SIGRTMIN..SIGRTMAX.
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