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    Subject[PATCH] Additional/catchup RCU signal fixes for -mm
    Hello!

    Additional RCU signal fixes to cover a race with exec() and to add
    some rcu_dereference()s from earlier patches.

    Signed-off-by: <paulmck@us.ibm.com>

    ---

    signal.c | 28 +++++++++++++++-------------
    1 files changed, 15 insertions(+), 13 deletions(-)

    diff -urpNa -X dontdiff linux-2.6.14-mm0/kernel/signal.c linux-2.6.14-mm0-fix/kernel/signal.c
    --- linux-2.6.14-mm0/kernel/signal.c 2005-11-04 14:37:18.000000000 -0800
    +++ linux-2.6.14-mm0-fix/kernel/signal.c 2005-11-04 17:23:40.000000000 -0800
    @@ -337,7 +337,7 @@ void exit_sighand(struct task_struct *ts
    write_lock_irq(&tasklist_lock);
    rcu_read_lock();
    if (tsk->sighand != NULL) {
    - struct sighand_struct *sighand = tsk->sighand;
    + struct sighand_struct *sighand = rcu_dereference(tsk->sighand);
    spin_lock(&sighand->siglock);
    __exit_sighand(tsk);
    spin_unlock(&sighand->siglock);
    @@ -352,13 +352,14 @@ void exit_sighand(struct task_struct *ts
    void __exit_signal(struct task_struct *tsk)
    {
    struct signal_struct * sig = tsk->signal;
    - struct sighand_struct * sighand = tsk->sighand;
    + struct sighand_struct * sighand;

    if (!sig)
    BUG();
    if (!atomic_read(&sig->count))
    BUG();
    rcu_read_lock();
    + sighand = rcu_dereference(tsk->sighand);
    spin_lock(&sighand->siglock);
    posix_cpu_timers_exit(tsk);
    if (atomic_dec_and_test(&sig->count)) {
    @@ -1100,7 +1101,7 @@ void zap_other_threads(struct task_struc
    }

    /*
    - * Must be called with the tasklist_lock held for reading!
    + * Must be called under rcu_read_lock() or with tasklist_lock read-held.
    */
    int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
    {
    @@ -1386,7 +1387,7 @@ send_sigqueue(int sig, struct sigqueue *
    {
    unsigned long flags;
    int ret = 0;
    - struct sighand_struct *sh = p->sighand;
    + struct sighand_struct *sh;

    BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));

    @@ -1405,7 +1406,15 @@ send_sigqueue(int sig, struct sigqueue *
    goto out_err;
    }

    +retry:
    + sh = rcu_dereference(p->sighand);
    +
    spin_lock_irqsave(&sh->siglock, flags);
    + if (p->sighand != sh) {
    + /* We raced with exec() in a multithreaded process... */
    + spin_unlock_irqrestore(&sh->siglock, flags);
    + goto retry;
    + }

    /*
    * We do the check here again to handle the following scenario:
    @@ -1464,15 +1473,8 @@ send_group_sigqueue(int sig, struct sigq

    BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));

    - while (!read_trylock(&tasklist_lock)) {
    - if (!p->sighand)
    - return -1;
    - cpu_relax();
    - }
    - if (unlikely(!p->sighand)) {
    - ret = -1;
    - goto out_err;
    - }
    + read_lock(&tasklist_lock);
    + /* Since it_lock is held, p->sighand cannot be NULL. */
    spin_lock_irqsave(&p->sighand->siglock, flags);
    handle_stop_signal(sig, p);

    -
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