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sched: fix TASK_WAKEKILL vs SIGKILL race

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schedule() has the special "TASK_INTERRUPTIBLE && signal_pending()" case,
this allows us to do

	current->state = TASK_INTERRUPTIBLE;
	schedule();

without fear to sleep with pending signal.

However, the code like

	current->state = TASK_KILLABLE;
	schedule();

is not right, schedule() doesn't take TASK_WAKEKILL into account. This means
that mutex_lock_killable(), wait_for_completion_killable(), down_killable(),
schedule_timeout_killable() can miss SIGKILL (and btw the second SIGKILL has
no effect).

Introduce the new helper, signal_pending_state(), and change schedule() to
use it. Hopefully it will have more users, that is why the task's state is
passed separately.

Note this "__TASK_STOPPED | __TASK_TRACED" check in signal_pending_state().
This is needed to preserve the current behaviour (ptrace_notify). I hope
this check will be removed soon, but this (afaics good) change needs the
separate discussion.

The fast path is "(state & (INTERRUPTIBLE | WAKEKILL)) + signal_pending(p)",
basically the same that schedule() does now. However, this patch of course
bloats schedule().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Oleg Nesterov 2008-06-08 21:20:41 +04:00 committed by Ingo Molnar
parent 39b945a37b
commit 16882c1e96
2 changed files with 15 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
include/linux/sched.h
View file

@ -2026,6 +2026,19 @@ static inline int fatal_signal_pending(struct task_struct *p)
return signal_pending(p) && __fatal_signal_pending(p);
}
static inline int signal_pending_state(long state, struct task_struct *p)
{
if (!(state & (TASK_INTERRUPTIBLE | TASK_WAKEKILL)))
return 0;
if (!signal_pending(p))
return 0;
if (state & (__TASK_STOPPED | __TASK_TRACED))
return 0;
return (state & TASK_INTERRUPTIBLE) || __fatal_signal_pending(p);
}
static inline int need_resched(void)
{
return unlikely(test_thread_flag(TIF_NEED_RESCHED));

6
kernel/sched.c
View file

@ -4159,12 +4159,10 @@ need_resched_nonpreemptible:
clear_tsk_need_resched(prev);
if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
if (unlikely((prev->state & TASK_INTERRUPTIBLE) &&
signal_pending(prev))) {
if (unlikely(signal_pending_state(prev->state, prev)))
prev->state = TASK_RUNNING;
} else {
else
deactivate_task(rq, prev, 1);
}
switch_count = &prev->nvcsw;
}