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    Subject[patch] clone-detached-2.5.31-A1

    the attached patch implements the per-CPU thread-structure cache to do
    detached exit, if the parent does not want to be notified of child exit
    via a signal. It works wondefully. (tested patch against BK-current.)

    i'm worried about one codepath though, in sys_wait4() we have this:

    p->parent = p->real_parent;
    add_parent(p, p->parent);
    do_notify_parent(p, SIGCHLD);

    can this actually trigger for a detached process as well? In any case i've
    put an assert in to make sure.

    Ingo

    --- linux/include/linux/sched.h.orig Tue Aug 13 20:27:23 2002
    +++ linux/include/linux/sched.h Tue Aug 13 20:50:18 2002
    @@ -47,6 +47,7 @@
    #define CLONE_SYSVSEM 0x00040000 /* share system V SEM_UNDO semantics */
    #define CLONE_SETTLS 0x00080000 /* create a new TLS for the child */
    #define CLONE_SETTID 0x00100000 /* write the TID back to userspace */
    +#define CLONE_DETACHED 0x00200000 /* parent wants no child-exit signal */

    #define CLONE_SIGNAL (CLONE_SIGHAND | CLONE_THREAD)

    --- linux/kernel/exit.c.orig Tue Aug 13 19:55:04 2002
    +++ linux/kernel/exit.c Tue Aug 13 20:52:46 2002
    @@ -56,10 +56,11 @@

    static void release_task(struct task_struct * p)
    {
    - if (p == current)
    + if (p->state != TASK_ZOMBIE)
    BUG();
    #ifdef CONFIG_SMP
    - wait_task_inactive(p);
    + if (p != current)
    + wait_task_inactive(p);
    #endif
    atomic_dec(&p->user->processes);
    security_ops->task_free_security(p);
    @@ -67,10 +68,12 @@
    unhash_process(p);

    release_thread(p);
    - current->cmin_flt += p->min_flt + p->cmin_flt;
    - current->cmaj_flt += p->maj_flt + p->cmaj_flt;
    - current->cnswap += p->nswap + p->cnswap;
    - sched_exit(p);
    + if (p != current) {
    + current->cmin_flt += p->min_flt + p->cmin_flt;
    + current->cmaj_flt += p->maj_flt + p->cmaj_flt;
    + current->cnswap += p->nswap + p->cnswap;
    + sched_exit(p);
    + }
    put_task_struct(p);
    }

    @@ -479,14 +482,15 @@

    write_lock_irq(&tasklist_lock);
    current->state = TASK_ZOMBIE;
    - do_notify_parent(current, current->exit_signal);
    + if (current->exit_signal != -1)
    + do_notify_parent(current, current->exit_signal);
    while ((p = eldest_child(current))) {
    list_del_init(&p->sibling);
    p->ptrace = 0;

    p->parent = p->real_parent;
    list_add_tail(&p->sibling,&p->parent->children);
    - if (p->state == TASK_ZOMBIE)
    + if (p->state == TASK_ZOMBIE && p->exit_signal != -1)
    do_notify_parent(p, p->exit_signal);
    /*
    * process group orphan check
    @@ -555,6 +559,9 @@

    tsk->exit_code = code;
    exit_notify();
    + preempt_disable();
    + if (current->exit_signal == -1)
    + release_task(current);
    schedule();
    BUG();
    /*
    --- linux/kernel/signal.c.orig Tue Aug 13 19:55:07 2002
    +++ linux/kernel/signal.c Tue Aug 13 20:53:43 2002
    @@ -768,12 +768,15 @@
    /*
    * Let a parent know about a status change of a child.
    */
    -
    void do_notify_parent(struct task_struct *tsk, int sig)
    {
    struct siginfo info;
    int why, status;

    + /* is the thread detached? */
    + if (sig == -1 || tsk->exit_signal == -1)
    + BUG();
    +
    info.si_signo = sig;
    info.si_errno = 0;
    info.si_pid = tsk->pid;
    @@ -823,9 +826,11 @@
    void
    notify_parent(struct task_struct *tsk, int sig)
    {
    - read_lock(&tasklist_lock);
    - do_notify_parent(tsk, sig);
    - read_unlock(&tasklist_lock);
    + if (sig != -1) {
    + read_lock(&tasklist_lock);
    + do_notify_parent(tsk, sig);
    + read_unlock(&tasklist_lock);
    + }
    }

    #ifndef HAVE_ARCH_GET_SIGNAL_TO_DELIVER
    --- linux/kernel/fork.c.orig Tue Aug 13 19:55:07 2002
    +++ linux/kernel/fork.c Tue Aug 13 20:47:03 2002
    @@ -50,6 +50,31 @@

    rwlock_t tasklist_lock __cacheline_aligned = RW_LOCK_UNLOCKED; /* outer */

    +/*
    + * A per-CPU task cache - this relies on the fact that
    + * the very last portion of sys_exit() is executed with
    + * preemption turned off.
    + */
    +static task_t *task_cache[NR_CPUS] __cacheline_aligned;
    +
    +void __put_task_struct(struct task_struct *tsk)
    +{
    + if (tsk != current) {
    + free_thread_info(tsk->thread_info);
    + kmem_cache_free(task_struct_cachep,tsk);
    + } else {
    + int cpu = smp_processor_id();
    +
    + tsk = task_cache[cpu];
    + if (tsk) {
    + free_thread_info(tsk->thread_info);
    + kmem_cache_free(task_struct_cachep,tsk);
    + }
    + task_cache[cpu] = current;
    + }
    +}
    +
    +/* Protects next_safe and last_pid. */
    void add_wait_queue(wait_queue_head_t *q, wait_queue_t * wait)
    {
    unsigned long flags;
    @@ -123,13 +148,6 @@
    return tsk;
    }

    -void __put_task_struct(struct task_struct *tsk)
    -{
    - free_thread_info(tsk->thread_info);
    - kmem_cache_free(task_struct_cachep,tsk);
    -}
    -
    -/* Protects next_safe and last_pid. */
    spinlock_t lastpid_lock = SPIN_LOCK_UNLOCKED;

    static int get_pid(unsigned long flags)
    @@ -737,7 +755,10 @@

    /* ok, now we should be set up.. */
    p->swappable = 1;
    - p->exit_signal = clone_flags & CSIGNAL;
    + if (clone_flags & CLONE_DETACHED)
    + p->exit_signal = -1;
    + else
    + p->exit_signal = clone_flags & CSIGNAL;
    p->pdeath_signal = 0;

    /*
    -
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