On 07/10, Eric W. Biederman wrote: > > > 2. To simplify, lets suppose we add the new PF_INFORK flag. Yes, this is > > bad, > > we can do better. I think we can simply add "struct hlist_head > > forking_threads" > > into signal_struct, so complete_signal() can just do > > hlist_for_each_entry() > > rather than for_each_thread() + PF_INFORK check. We don't even need a new > > member in task_struct. > > We still need the distinction between multi-process signals and single > process signals (which is the hard part). For good performance of > signal delivery to multi-threaded tasks we still need a new member in > signal_struct. Plus it is a bit more work to update the list or even > walk the list than a sequence counter. > > So I think adding a sequence counter to let us know about multiprocess > signals is the local optimum.
But we can not rely on on a sequence counter, there are other reasons why fork() should fail even if fatal_signal_pending() == F and the counter was not changed (no multi-process signals). > > 3. copy_process() can simply block/unblock all signals (except KILL/STOP), > > see > > the "patch" below. > > All signals are effectively blocked for the duration of the fork for the > calling task. Where we get into trouble and where we need a fix for > correctness is that another thread can dequeue the signal. Blocking > signals of the forking task does not change that. See my reply to Linus. Please look at the change in complete_signal(). > I think that reveals another bug in our current logic. For blocked > multi-process signals we don't ensure they get delivered to both the > parent and the child if the signal logically comes in after the fork. I thougth thought this too. I simply do not know if this is right or not. For now I assume that this is correct and by design, iow if fork() is called with (say) SIGTERM blocked, then we do not care if kill_pgrp(SIGTERM) misses the new child. If we want to change this, I think this needs another discussion. Oleg.
