Commit 7bb44ade authored by Roland McGrath's avatar Roland McGrath Committed by Linus Torvalds
Browse files

recalc_sigpending_tsk fixes 



Steve Hawkes discovered a problem where recalc_sigpending_tsk was called in
do_sigaction but no signal_wake_up call was made, preventing later signals
from waking up blocked threads with TIF_SIGPENDING already set.

In fact, the few other calls to recalc_sigpending_tsk outside the signals
code are also subject to this problem in other race conditions.

This change makes recalc_sigpending_tsk private to the signals code.  It
changes the outside calls, as well as do_sigaction, to use the new
recalc_sigpending_and_wake instead.

Signed-off-by: default avatarRoland McGrath <roland@redhat.com>
Cc: <Steve.Hawkes@motorola.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3c6df2a9

include/linux/sched.h

+7 −5
Original line number Diff line number Diff line
@@ -1616,11 +1616,13 @@ static inline int lock_need_resched(spinlock_t *lock) 
	return 0;

}



/* Reevaluate whether the task has signals pending delivery.

   This is required every time the blocked sigset_t changes.

   callers must hold sighand->siglock.  */



extern FASTCALL(void recalc_sigpending_tsk(struct task_struct *t));

/*

 * Reevaluate whether the task has signals pending delivery.

 * Wake the task if so.

 * This is required every time the blocked sigset_t changes.

 * callers must hold sighand->siglock.

 */

extern void recalc_sigpending_and_wake(struct task_struct *t);

extern void recalc_sigpending(void);



extern void signal_wake_up(struct task_struct *t, int resume_stopped);

kernel/exit.c

+2 −5
Original line number Diff line number Diff line
@@ -762,11 +762,8 @@ static void exit_notify(struct task_struct *tsk) 
		read_lock(&tasklist_lock);

		spin_lock_irq(&tsk->sighand->siglock);

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

			if (!signal_pending(t) && !(t->flags & PF_EXITING)) {

				recalc_sigpending_tsk(t);

				if (signal_pending(t))

					signal_wake_up(t, 0);

			}

			if (!signal_pending(t) && !(t->flags & PF_EXITING))

				recalc_sigpending_and_wake(t);

		spin_unlock_irq(&tsk->sighand->siglock);

		read_unlock(&tasklist_lock);

	}

kernel/power/process.c

+1 −1
Original line number Diff line number Diff line
@@ -101,7 +101,7 @@ static void cancel_freezing(struct task_struct *p) 
		pr_debug("  clean up: %s\n", p->comm);

		do_not_freeze(p);

		spin_lock_irqsave(&p->sighand->siglock, flags);

		recalc_sigpending_tsk(p);

		recalc_sigpending_and_wake(p);

		spin_unlock_irqrestore(&p->sighand->siglock, flags);

	}

}

kernel/signal.c

+18 −6
Original line number Diff line number Diff line
@@ -96,15 +96,27 @@ static inline int has_pending_signals(sigset_t *signal, sigset_t *blocked) 


#define PENDING(p,b) has_pending_signals(&(p)->signal, (b))



fastcall void recalc_sigpending_tsk(struct task_struct *t)

static int recalc_sigpending_tsk(struct task_struct *t)

{

	if (t->signal->group_stop_count > 0 ||

	    (freezing(t)) ||

	    PENDING(&t->pending, &t->blocked) ||

	    PENDING(&t->signal->shared_pending, &t->blocked))

	    PENDING(&t->signal->shared_pending, &t->blocked)) {

		set_tsk_thread_flag(t, TIF_SIGPENDING);

	else

		return 1;

	}

	clear_tsk_thread_flag(t, TIF_SIGPENDING);

	return 0;

}



/*

 * After recalculating TIF_SIGPENDING, we need to make sure the task wakes up.

 * This is superfluous when called on current, the wakeup is a harmless no-op.

 */

void recalc_sigpending_and_wake(struct task_struct *t)

{

	if (recalc_sigpending_tsk(t))

		signal_wake_up(t, 0);

}



void recalc_sigpending(void)
@@ -744,7 +756,7 @@ force_sig_info(int sig, struct siginfo *info, struct task_struct *t) 
		action->sa.sa_handler = SIG_DFL;

		if (blocked) {

			sigdelset(&t->blocked, sig);

			recalc_sigpending_tsk(t);

			recalc_sigpending_and_wake(t);

		}

	}

	ret = specific_send_sig_info(sig, info, t);
@@ -2273,7 +2285,7 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact) 
			rm_from_queue_full(&mask, &t->signal->shared_pending);

			do {

				rm_from_queue_full(&mask, &t->pending);

				recalc_sigpending_tsk(t);

				recalc_sigpending_and_wake(t);

				t = next_thread(t);

			} while (t != current);

		}

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