Sorry, I didn't look at other patches, but this one looks strange
to me...
On 09/23, Michael Holzheu wrote:
>
> Currently there are code pathes (e.g. for kthreads) where the consumed
> CPU time is not accounted to the parents cumulative counters.
Could you explain more?
> +static void account_to_parent(struct task_struct *p)
> +{
> + struct signal_struct *psig, *sig;
> + struct task_struct *tsk_parent;
> +
> + read_lock(&tasklist_lock);
No need to take tasklist, you can use rcu_read_lock() if you need
get_task_struct(). But this can't help, please see below.
> + tsk_parent = p->real_parent;
> + if (!tsk_parent) {
> + read_unlock(&tasklist_lock);
> + return;
> + }
> + get_task_struct(tsk_parent);
> + read_unlock(&tasklist_lock);
> +
> + // printk("XXX Fix accounting: pid=%d ppid=%d\n", p->pid, tsk_parent->pid);
> + spin_lock_irq(&tsk_parent->sighand->siglock);
This is racy. ->real_parent can exit after we drop tasklist_lock,
->sighand can be NULL.
> void release_task(struct task_struct * p)
> {
> struct task_struct *leader;
> int zap_leader;
> +
> + if (!p->exit_accounting_done)
> + account_to_parent(p);
> repeat:
> tracehook_prepare_release_task(p);
> /* don't need to get the RCU readlock here - the process is dead and
> @@ -1279,6 +1313,7 @@
> psig->cmaxrss = maxrss;
> task_io_accounting_add(&psig->ioac, &p->ioac);
> task_io_accounting_add(&psig->ioac, &sig->ioac);
> + p->exit_accounting_done = 1;
Can't understand.
Suppose that a thread T exits and reaps itself (calls release_task).
Now we call account_to_parent() which accounts T->signal->XXX + T->XXX.
After that T calls __exit_signal and does T->signal->XXX += T->XXX.
If another thread exits it does the same and we account the already
exited thread T again?
When the last thread exits, wait_task_zombie() accounts T->signal
once again.
IOW, this looks like the over-accounting to me, no?
Oleg.
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