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Commit 25f407f0 authored by Roland McGrath's avatar Roland McGrath Committed by Linus Torvalds
Browse files

[PATCH] Call exit_itimers from do_exit, not __exit_signal 



When I originally moved exit_itimers into __exit_signal, that was the only
place where we could reliably know it was the last thread in the group
dying, without races.  Since then we've gotten the signal_struct.live
counter, and do_exit can reliably do group-wide cleanup work.

This patch moves the call to do_exit, where it's made without locks.  This
avoids the deadlock issues that the old __exit_signal code's comment talks
about, and the one that Oleg found recently with process CPU timers.

[ This replaces e03d13e9, which is why
  it was just reverted. ]

Signed-off-by: default avatarRoland McGrath <roland@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 9465bee8

kernel/exit.c

+1 −0
Original line number Diff line number Diff line
@@ -843,6 +843,7 @@ fastcall NORET_TYPE void do_exit(long code) 
	group_dead = atomic_dec_and_test(&tsk->signal->live);

	if (group_dead) {

 		del_timer_sync(&tsk->signal->real_timer);

		exit_itimers(tsk->signal);

		acct_process(code);

	}

	exit_mm(tsk);

kernel/posix-timers.c

+1 −1
Original line number Diff line number Diff line
@@ -1157,7 +1157,7 @@ static inline void itimer_delete(struct k_itimer *timer) 
}



/*

 * This is called by __exit_signal, only when there are no more

 * This is called by do_exit or de_thread, only when there are no more

 * references to the shared signal_struct.

 */

void exit_itimers(struct signal_struct *sig)

kernel/signal.c

+1 −13
Original line number Diff line number Diff line
@@ -397,20 +397,8 @@ void __exit_signal(struct task_struct *tsk) 
	flush_sigqueue(&tsk->pending);

	if (sig) {

		/*

		 * We are cleaning up the signal_struct here.  We delayed

		 * calling exit_itimers until after flush_sigqueue, just in

		 * case our thread-local pending queue contained a queued

		 * timer signal that would have been cleared in

		 * exit_itimers.  When that called sigqueue_free, it would

		 * attempt to re-take the tasklist_lock and deadlock.  This

		 * can never happen if we ensure that all queues the

		 * timer's signal might be queued on have been flushed

		 * first.  The shared_pending queue, and our own pending

		 * queue are the only queues the timer could be on, since

		 * there are no other threads left in the group and timer

		 * signals are constrained to threads inside the group.

		 */

		exit_itimers(sig);

		 * We are cleaning up the signal_struct here.

		 */

		exit_thread_group_keys(sig);

		kmem_cache_free(signal_cachep, sig);

	}