Messages in this thread | | | Date | Fri, 31 Aug 2012 13:06:32 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 02/14] aoe: kernel thread handles I/O completions for simple locking |
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On Sat, 25 Aug 2012 10:39:46 -0400 Ed Cashin <ecashin@coraid.com> wrote:
> +static int > +kthread(void *vp) > +{ > + struct ktstate *k; > + DECLARE_WAITQUEUE(wait, current); > + int more; > + > + k = vp; > + current->flags |= PF_NOFREEZE; > + set_user_nice(current, -10); > + complete(&k->rendez); /* tell spawner we're running */ > + do { > + spin_lock_irq(k->lock); > + more = k->fn(); > + if (!more) { > + add_wait_queue(k->waitq, &wait); > + __set_current_state(TASK_INTERRUPTIBLE); > + } > + spin_unlock_irq(k->lock); > + if (!more) { > + schedule(); > + remove_wait_queue(k->waitq, &wait); > + } else > + cond_resched(); > + } while (!kthread_should_stop()); > + complete(&k->rendez); /* tell spawner we're stopping */ > + return 0; > +} > + > +static void > +aoe_ktstop(struct ktstate *k) > +{ > + kthread_stop(k->task); > + wait_for_completion(&k->rendez); > +} > + > +static int > +aoe_ktstart(struct ktstate *k) > +{ > + struct task_struct *task; > + > + init_completion(&k->rendez); > + task = kthread_run(kthread, k, k->name); > + if (task == NULL || IS_ERR(task)) > + return -ENOMEM; > + k->task = task; > + wait_for_completion(&k->rendez); /* allow kthread to start */ > + init_completion(&k->rendez); /* for waiting for exit later */ > + return 0; > +}
It's a pretty unlikely thing, but I wonder if there's a way in which aoe_ktstart() can run that second init_completion() _after_ kthread() has run its second complete(). ie: someone runs aoe_ktstop() super-early. If that can happen, the later wait_for_completion() hangs up.
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