lkml.org 
[lkml]   [2005]   [Aug]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    SubjectRe: [PATCH 2.6.13-rc6-rt9] PI aware dynamic priority adjustment
    From
    Date
    On Sat, 2005-08-20 at 18:10 +0400, Oleg Nesterov wrote:

    > posix_timer_event() first checks that the thread (SIGEV_THREAD_ID
    > case) does not have PF_EXITING flag, then it calls send_sigqueue()
    > which locks task list. But if the thread exits in between the kernel
    > will oops.

    > posix_timer_event() runs under k_itimer.it_lock, but this does not
    > help if that thread was not the only one in thread group, in this
    > case we don't call exit_itimers().

    I added exit_notify_itimers() for that case. It is synchronized vs.
    posix_timer_event() via the timer lock and therefor protects against the
    race described above.

    It solves the problem for the only user of send_sigqueue for now, but I
    think we should have a more general interface to such functionality to
    allow simple usage.

    tglx

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>


    diff -uprN --exclude-from=/usr/local/bin/diffit.exclude linux-2.6.13-rc6/include/linux/sched.h linux-2.6.13-rc6.work/include/linux/sched.h
    --- linux-2.6.13-rc6/include/linux/sched.h 2005-08-13 12:25:56.000000000 +0200
    +++ linux-2.6.13-rc6.work/include/linux/sched.h 2005-08-20 17:43:36.000000000 +0200
    @@ -1051,6 +1051,7 @@ extern void __exit_signal(struct task_st
    extern void exit_sighand(struct task_struct *);
    extern void __exit_sighand(struct task_struct *);
    extern void exit_itimers(struct signal_struct *);
    +extern void exit_notify_itimers(struct signal_struct *);

    extern NORET_TYPE void do_group_exit(int);

    diff -uprN --exclude-from=/usr/local/bin/diffit.exclude linux-2.6.13-rc6/kernel/posix-timers.c linux-2.6.13-rc6.work/kernel/posix-timers.c
    --- linux-2.6.13-rc6/kernel/posix-timers.c 2005-08-13 12:25:58.000000000 +0200
    +++ linux-2.6.13-rc6.work/kernel/posix-timers.c 2005-08-20 17:43:36.000000000 +0200
    @@ -1169,6 +1169,33 @@ void exit_itimers(struct signal_struct *
    }

    /*
    + * This is called by __exit_signal, when there are still references to
    + * the shared signal_struct
    + */
    +void exit_notify_itimers(struct signal_struct *sig)
    +{
    + struct k_itimer *timer;
    + struct list_head *tmp;
    + unsigned long flags;
    +
    + list_for_each(tmp, &sig->posix_timers) {
    +
    + timer = list_entry(tmp, struct k_itimer, list);
    +
    + /* Protect against posix_timer_fn */
    + spin_lock_irqsave(&timer->it_lock, flags);
    + if (timer->it_process == current) {
    +
    + if (timer->it_sigev_notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
    + timer->it_sigev_notify = SIGEV_SIGNAL;
    +
    + timer->it_process = timer->it_process->group_leader;
    + }
    + spin_lock_irqrestore(&timer->it_lock, flags);
    + }
    +}
    +
    +/*
    * And now for the "clock" calls
    *
    * These functions are called both from timer functions (with the timer
    diff -uprN --exclude-from=/usr/local/bin/diffit.exclude linux-2.6.13-rc6/kernel/signal.c linux-2.6.13-rc6.work/kernel/signal.c
    --- linux-2.6.13-rc6/kernel/signal.c 2005-08-13 12:25:58.000000000 +0200
    +++ linux-2.6.13-rc6.work/kernel/signal.c 2005-08-20 17:57:46.000000000 +0200
    @@ -390,6 +390,7 @@ void __exit_signal(struct task_struct *t
    sig->nvcsw += tsk->nvcsw;
    sig->nivcsw += tsk->nivcsw;
    sig->sched_time += tsk->sched_time;
    + exit_notify_itimers(sig);
    spin_unlock(&sighand->siglock);
    sig = NULL; /* Marker for below. */
    }
    @@ -1381,13 +1382,12 @@ send_sigqueue(int sig, struct sigqueue *
    int ret = 0;

    /*
    - * We need the tasklist lock even for the specific
    - * thread case (when we don't need to follow the group
    - * lists) in order to avoid races with "p->sighand"
    - * going away or changing from under us.
    + * No need to hold tasklist lock here.
    + * posix_timer_event() is synchronized via
    + * exit_itimers() and exit_notify_itimers() to
    + * be protected against p->sighand == NULL
    */
    BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
    - read_lock(&tasklist_lock);
    spin_lock_irqsave(&p->sighand->siglock, flags);

    if (unlikely(!list_empty(&q->list))) {
    @@ -1414,7 +1414,6 @@ send_sigqueue(int sig, struct sigqueue *

    out:
    spin_unlock_irqrestore(&p->sighand->siglock, flags);
    - read_unlock(&tasklist_lock);
    return(ret);
    }


    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-08-20 18:07    [W:0.028 / U:0.220 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site