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    SubjectRe: [PATCH 4 of 4] Introduce aio system call submission and completion system calls
    On Tue, 30 Jan 2007, Zach Brown wrote:

    > +void asys_task_exiting(struct task_struct *tsk)
    > +{
    > + struct asys_result *res, *next;
    > +
    > + list_for_each_entry_safe(res, next, &tsk->asys_completed, item)
    > + kfree(res);
    > +
    > + /*
    > + * XXX this only works if tsk->fibril was allocated by
    > + * sys_asys_submit(), not if its embedded in an asys_call. This
    > + * implies that we must forbid sys_exit in asys_submit.
    > + */
    > + if (tsk->fibril) {
    > + BUG_ON(!list_empty(&tsk->fibril->run_list));
    > + kfree(tsk->fibril);
    > + tsk->fibril = NULL;
    > + }
    > +}

    What happens to lingering fibrils? Better keep track of both runnable and
    sleepers, and do proper cleanup.



    > +asmlinkage long sys_asys_submit(struct asys_input __user *user_inp,
    > + unsigned long nr_inp)
    > +{
    > + struct asys_input inp;
    > + struct asys_result *res;
    > + struct asys_call *call;
    > + struct thread_info *ti;
    > + unsigned long i;
    > + long err = 0;
    > +
    > + /* Allocate a fibril for the submitter's thread_info */
    > + if (current->fibril == NULL) {
    > + current->fibril = kzalloc(sizeof(struct fibril), GFP_KERNEL);
    > + if (current->fibril == NULL)
    > + return -ENOMEM;
    > +
    > + INIT_LIST_HEAD(&current->fibril->run_list);
    > + current->fibril->state = TASK_RUNNING;
    > + current->fibril->ti = current_thread_info();
    > + }

    Why do we need the "special" submission fibril?




    > + for (i = 0; i < nr_inp; i++) {
    > +
    > + if (copy_from_user(&inp, &user_inp[i], sizeof(inp))) {
    > + err = -EFAULT;
    > + break;
    > + }
    > +
    > + res = kmalloc(sizeof(struct asys_result), GFP_KERNEL);
    > + if (res == NULL) {
    > + err = -ENOMEM;
    > + break;
    > + }
    > +
    > + /* XXX kzalloc to init call.fibril.per_cpu, add helper */
    > + call = kzalloc(sizeof(struct asys_call), GFP_KERNEL);
    > + if (call == NULL) {
    > + kfree(res);
    > + err = -ENOMEM;
    > + break;
    > + }
    > +
    > + ti = alloc_thread_info(tsk);
    > + if (ti == NULL) {
    > + kfree(res);
    > + kfree(call);
    > + err = -ENOMEM;
    > + break;
    > + }
    > +
    > + err = asys_init_fibril(&call->fibril, ti, &inp);
    > + if (err) {
    > + kfree(res);
    > + kfree(call);
    > + free_thread_info(ti);
    > + break;
    > + }
    > +
    > + res->comp.cookie = inp.cookie;
    > + call->result = res;
    > + ti->task = current;
    > +
    > + sched_new_runnable_fibril(&call->fibril);
    > + schedule();
    > + }
    > +
    > + return i ? i : err;
    > +}

    Streamline error path (kfree(NULL) is OK):

    err = -ENOMEM;
    a = alloc();
    b = alloc();
    c = alloc();
    if (!a || !b || !c)
    goto error;
    ...
    error:
    kfree(c);
    kfree(b);
    kfree(a);
    return err;


    - Davide


    -
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