PATCH: freezer: add fake signal clearing back when thaw task

[Lianwei Wang]

 Hi Tejun Heo and all,

The commit of "34b087e freezer: kill unused
set_freezable_with_signal()" remove recalc_sigpending*() calls in
freezer, so the user tasks get TIF_SIGPENDING fake signal that is set
when freezing userspace process. It left the fake signal to userspcae
which cause the userspace task that wait_event_freezable and friends
return a wrong ERESTARTSYS. This is not good because it waste cpu time
to handle the fake signal.

Can we just call the recalc_sigpending to clear the fake signal for
userspace tasks? as below patch do: