kthread() sleeps in TASK_INTERRUPTIBLE state waiting for the first wakeup.  In
theory, this wakeup may come from freeze_process()->signal_wake_up(), so the
task can disappear even before kthread_create() sets its ->comm.

Change kthread() to use TASK_UNINTERRUPTIBLE.

[akpm@linux-foundation.org: s/BUG_ON/WARN_ON+recover]
Signed-off-by: NOleg Nesterov <oleg@tv-sign.ru>
Acked-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>