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Commit a122b341 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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[PATCH] do_signal_stop: don't take tasklist_lock 



do_signal_stop() does not need tasklist_lock anymore.  So it does not need to
do misc re-checks, and we can simplify the code.

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 6108ccd3

kernel/signal.c

+17 −52
Original line number Diff line number Diff line
@@ -1682,8 +1682,7 @@ finish_stop(int stop_count) 
 * Returns nonzero if we've actually stopped and released the siglock.

 * Returns zero if we didn't stop and still hold the siglock.

 */

static int

do_signal_stop(int signr)

static int do_signal_stop(int signr)

{

	struct signal_struct *sig = current->signal;

	struct sighand_struct *sighand = current->sighand;
@@ -1703,7 +1702,6 @@ do_signal_stop(int signr) 
		set_current_state(TASK_STOPPED);

		if (stop_count == 0)

			sig->flags = SIGNAL_STOP_STOPPED;

		spin_unlock_irq(&sighand->siglock);

	}

	else if (thread_group_empty(current)) {

		/*
@@ -1712,44 +1710,20 @@ do_signal_stop(int signr) 
		current->exit_code = current->signal->group_exit_code = signr;

		set_current_state(TASK_STOPPED);

		sig->flags = SIGNAL_STOP_STOPPED;

		spin_unlock_irq(&sighand->siglock);

	}

	else {

		/*

		 * (sig->group_stop_count == 0)

		 * There is no group stop already in progress.

		 * We must initiate one now, but that requires

		 * dropping siglock to get both the tasklist lock

		 * and siglock again in the proper order.  Note that

		 * this allows an intervening SIGCONT to be posted.

		 * We need to check for that and bail out if necessary.

		 * We must initiate one now.

		 */

		struct task_struct *t;



		spin_unlock_irq(&sighand->siglock);



		/* signals can be posted during this window */



		read_lock(&tasklist_lock);

		spin_lock_irq(&sighand->siglock);



		if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED)) {

			/*

			 * Another stop or continue happened while we

			 * didn't have the lock.  We can just swallow this

			 * signal now.  If we raced with a SIGCONT, that

			 * should have just cleared it now.  If we raced

			 * with another processor delivering a stop signal,

			 * then the SIGCONT that wakes us up should clear it.

			 */

			read_unlock(&tasklist_lock);

			return 0;

		}



		if (sig->group_stop_count == 0) {

		current->exit_code = signr;

		sig->group_exit_code = signr;



		stop_count = 0;

			for (t = next_thread(current); t != current;

			     t = next_thread(t))

		for (t = next_thread(current); t != current; t = next_thread(t))

			/*

			 * Setting state to TASK_STOPPED for a group

			 * stop is always done with the siglock held,
@@ -1761,22 +1735,13 @@ do_signal_stop(int signr) 
				signal_wake_up(t, 0);

			}

		sig->group_stop_count = stop_count;

		}

		else {

			/* A race with another thread while unlocked.  */

			signr = sig->group_exit_code;

			stop_count = --sig->group_stop_count;

		}



		current->exit_code = signr;

		set_current_state(TASK_STOPPED);

		if (stop_count == 0)

			sig->flags = SIGNAL_STOP_STOPPED;



		spin_unlock_irq(&sighand->siglock);

		read_unlock(&tasklist_lock);

	}



	spin_unlock_irq(&sighand->siglock);

	finish_stop(stop_count);

	return 1;

}