Hi,
On 09/06, Tejun Heo wrote:
>
> Hello,
>
> On Mon, Sep 05, 2011 at 06:20:12PM +0200, Oleg Nesterov wrote:
> > Perhaps it is correct... Just I do not understand what it should do.
> > I thought it is "wait_for_event && do_not_block_freezer". And at first
> > glance the code looks as if it tries to do this. Say, in the "likely"
> > case we restart wait_event_interruptible() after refrigerator().
> >
> > But this looks racy. Suppose that freezing() is already false when
> > try_to_freeze() or __refrigerator() is called. Say, cgroup_freezer does
> > freeze_task() + __thaw_task(). Why it returns -ERESTARTSYS in this case?
>
> It may return -ERESTARTSYS when not strictly necessary but given that
> it's supposed to trigger restart anyway I don't think it's actually
> broken (it doesn't break the contract of the wait).
OK, but still this doesn't look right.
> Another thing to
> note is that kthread freezing via cgroup is almost fundamentally
> broken.
OK, let it be freeze_processes()+thaw_tasks(). Of course this is mostly
theoretical.
> > And if it can be used by the userspace thread, then we should probably
> > do recalc_sigpending() somewhere, otherwise wait_event_freezable() will
> > always return -ERESTARTSYS after __refrigerator().
>
> Thankfully, currently, all the few users are kthreads. I don't think
> it makes sense for userland tasks at all.
Yes, agreed. In this case I think it should be
#define wait_event_freezable(wq, condition) \
({ \
int __retval; \
for (;;) { \
__retval = wait_event_interruptible(wq, \
(condition) || freezing(current)); \
if (__retval || (condition)) \
break; \
try_to_freeze(); \
} \
__retval; \
})
__retval/ERESTARTSYS is only needed for kthreads which play with allow_signal(),
probably nobody should do this.
Oleg.
_______________________________________________
linux-pm mailing list
linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linux-foundation.org/mailman/listinfo/linux-pm
