exit: exit_notify() can trust signal->notify_count < 0
authorOleg Nesterov <oleg@redhat.com>
Wed, 26 May 2010 21:43:10 +0000 (14:43 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 27 May 2010 16:12:45 +0000 (09:12 -0700)
commit9c3391684415c9dca239130d9e433a60a4edf04b
treea8019b964c625cfeeda0e9d85bafa48991546212
parent269b005a28e124a341df4adef2c3661cf7371fcc
exit: exit_notify() can trust signal->notify_count < 0

signal_struct->count in its current form must die.

- it has no reasons to be atomic_t

- it looks like a reference counter, but it is not

- otoh, we really need to make task->signal refcountable, just look at
  the extremely ugly task_rq_unlock_wait() called from __exit_signals().

- we should change the lifetime rules for task->signal, it should be
  pinned to task_struct.  We have a lot of code which can be simplified
  after that.

- it is not needed!  while the code is correct, any usage of this
  counter is artificial, except fs/proc uses it correctly to show the
  number of threads.

This series removes the usage of sig->count from exit pathes.

This patch:

Now that Veaceslav changed copy_signal() to use zalloc(), exit_notify()
can just check notify_count < 0 to ensure the execing sub-threads needs
the notification from us.  No need to do other checks, notify_count != 0
must always mean ->group_exit_task != NULL is waiting for us.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/exit.c