On Wed, Nov 14, 2018 at 05:56:32PM +0100, Oleg Nesterov wrote: > Hi Roman, > > On 11/13, Roman Gushchin wrote: > > > > > > +#define TASK_FROZEN 0x1000 > > > > +#define TASK_STATE_MAX 0x2000 > > > > > > Just noticed the new task state... Why? Can't we avoid it? > > > > We can, but it's nice to show to userspace that tasks are frozen, > > rather than just stuck somewhere in the kernel... > > But then you need to change get_task_state() too. Which iiuc could > probably check ->frozen along with ->state. > > I do not think the new task state is a good idea, at least I would like > to ask you to make a separate patch which we can discuss separately. Yeah, I have separated it in v3. > > > > > > + set_current_state(TASK_WAKEKILL | TASK_INTERRUPTIBLE | TASK_FROZEN); > > > > > > Why not __set_current_state() ? > > > > Hm, it's not a hot path at all, so set_current_state() is good enough. > > Not a strong preference, of course. > > It is not about performance, to me set_current_state() looks as if we need > a memory barrier for some obscure/undocumented reason and this doesn't help > to understand the code. > > > > If ->state include TASK_INTERRUPTIBLE, why do we need TASK_WAKEKILL? > > > > > > And again, why TASK_FROZEN? > > > > So, should it be just TASK_INTERRUPTIBLE | TASK_FROZEN ? > > Again, TASK_FROZEN is pointless at least until you change fs/proc or until > you have wake_up_state(TASK_FROZEN). May be cgroup_do_freeze() and/or > ptrace_attach() could use it, but see above, I'd suggest to make another > patch. > > Looks like you need TASK_KILLABLE, see below. > > > > > + clear_thread_flag(TIF_SIGPENDING); > > > > + schedule(); > > > > + recalc_sigpending(); > > > > > > I simply can't understand these 3 lines above but I bet this is not correct ;) > > > > So, yeah, the problem is that if there is TIF_SIGPENDING bit set, schedule() > > will return immediately, so we're getting pretty much a busy loop here. > > I suspected this answer ;) > > > This is a nasty workaround. > > No, this is very wrong. Just suppose the caller is killed right before > clear_thread_flag(TIF_SIGPENDING). So, I had TASK_KILLABLE before, but had some issues with ptrace/gdb. I'll revisit this option. > > > I believe we can clear and not call recalc_sigpending() at all. Does this seem > > to be correct? > > I think you need to simply remove both clear_thread_flag() and recalc_sigpending(). > If schedule() is called in TASK_KILLABLE state it will return only if > fatal_signal_pending() is true, and this is what we want, right? > > OK, it seems you are going to make the new version anyway, so I can wait for it > and not read this series ;) Sure! I'm about to post it. Thanks!
