Messages in this thread Patch in this message | | | Date | Sun, 8 Jun 2008 21:20:41 +0400 | From | Oleg Nesterov <> | Subject | [PATCH 1/3] 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>
include/linux/sched.h | 13 +++++++++++++ kernel/sched.c | 6 ++---- 2 files changed, 15 insertions(+), 4 deletions(-)
--- 26-rc2/include/linux/sched.h~1_SP_STATE 2008-06-01 16:44:39.000000000 +0400 +++ 26-rc2/include/linux/sched.h 2008-06-01 16:44:39.000000000 +0400 @@ -2027,6 +2027,19 @@ static inline int fatal_signal_pending(s 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_tsk_need_resched(current)); --- 26-rc2/kernel/sched.c~1_SP_STATE 2008-06-08 16:15:25.000000000 +0400 +++ 26-rc2/kernel/sched.c 2008-06-08 16:52:23.000000000 +0400 @@ -4510,12 +4510,10 @@ 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; }
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