On Wed 14-11-18 19:18:42, Chanho Min wrote: > > > > It's been some time since I have looked into this code so bear with > me. > > > > One thing is not really clear to me. Why does it help to exclude this > > > > particular task from the freezer > > > > > > we don't exclude it, > > > > > > > when it is not sleeping in the freezer. > > > > > > Yes, it is not sleeping in __refrigerator(), but it does > > > > > > schedule(); > > > freezer_count(); > > > > > > so it will enter __refrigerator() right after wakeup. If it won't be > > woken > > > up we do not care, we can consider it "frozen". > > > > Right, but this is just silencing the freezing code to exclude this > > task, right? > > > > > > I can see how other threads need to be zapped and TASK_WAKEKILL > > doesn't > > > > do that but shouldn't we fix that instead? > > > > > > Not sure I understand, but unlikely we can (or want) to make > > __refrigerator() > > > killable. > > > > Why would that be a problem. If the kill is fatal then why to keep the > > killed task in the fridge? > > > > Is it different between 'the killed task is frozen' and '__refrigerator() > is killable'? > From a general '__refrigerator()' implementation point of view I know that > it should not be killable. Is that because there are many paths that do not terminate right after the task get out of the fridge? Like the signal path? > > > Otherwise, how can we fix that? > > > > We can mark all threads PF_NOFREEZE and wake them up. This would require > > some more changes of course but wouldn't that be a more appropriate > > solution? Do we want to block exec for ever just because some threads > > are in the fridge? > > > > IMHO, It seems to be difficult and buggy to control with PF_NOFREEZE. > Because, > The sub-thread can freeze and receive SIG_KILL before the marking of > PF_NOFREEZE > and it should be freezable in other cases. But we do control the ordering in this path no? > I don't understand why it isn't appropriate for exec to block. The > exec can freeze. When tasks are thawed, the killed sub-thread will die > and wake de_thread(). The exec will continue to work from resume. Because this is fragile. I haven't checked the full set of resources the task holds when in this path but I can imagine we can introduce lock dependency on freezing really easily. -- Michal Hocko SUSE Labs
