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    SubjectRe: [patch 2/13] signal/timer/event fds v6 - signalfd core ...
    On Mon, 19 Mar 2007, Oleg Nesterov wrote:

    > On 03/19, Davide Libenzi wrote:
    > >
    > > On Mon, 19 Mar 2007, Eric W. Biederman wrote:
    > >
    > > > > +struct signalfd_ctx {
    > > > > + struct list_head lnk;
    > > > > + wait_queue_head_t wqh;
    > > > > + sigset_t sigmask;
    > > > > + struct task_struct *tsk;
    > > > > +};
    > > >
    > > > I think you want to use a struct pid *pid instead of a pointer to the
    > > > task struct here. It is slightly less efficient (one more
    > > > dereference) but it means that we won't pin the task struct in memory
    > > > indefinitely. Pinning the task_struct like this makes for a very
    > > > interesting way to get around the limits on the number of processes a
    > > > user can have.
    > >
    > > Hmm, when the task is detached from the sighand, we get a notify, so I
    > > could do a put from there. This would avoid the extra de-reference. I need
    > > to verify locking though ...
    >
    > In that case (if I understand you correctly) we don't need {get,put}_task_struct()
    > at all.
    >
    > signalfd_deliver(-1) sets ctx->tsk = NULL, signalfd_get_sighand() reads ->tsk
    > under rcu_read_lock(). The code becomes even simpler, we don't need to check
    > list_empty(&ctx->lnk).

    I'd need a get_task_struct in any case in order to safely call
    unlock_task_sighand(). At that point I'd prefer to just pass through the
    struct pid*. I'll be posting the new version for review as soon as I
    complete a few tests ...



    - Davide


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