Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH v3 10/19] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() | Date | Thu, 15 Oct 2020 14:54:53 +0100 |
| |
On 15/10/20 12:05, Peter Zijlstra wrote: > +static int affine_move_task(struct rq *rq, struct rq_flags *rf, > + struct task_struct *p, int dest_cpu, unsigned int flags) > +{ > + struct set_affinity_pending my_pending = { }, *pending = NULL; > + struct migration_arg arg = { > + .task = p, > + .dest_cpu = dest_cpu, > + }; > + bool complete = false; > + > + /* Can the task run on the task's current CPU? If so, we're done */ > + if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) { > + pending = p->migration_pending; > + if (pending) { > + p->migration_pending = NULL; > + complete = true;
Deciphering my TLA+ deadlock traces leads me to think this needs
refcount_inc(&pending->refs);
because the 'goto do_complete' leads us to an unconditional decrement.
> + } > + task_rq_unlock(rq, p, rf); > + > + if (complete) > + goto do_complete; ^^^^ that here
> + > + return 0; > + } > +
[...]
> +do_complete: > + if (complete) > + complete_all(&pending->done); > + } > + > + wait_for_completion(&pending->done); > + > + if (refcount_dec_and_test(&pending->refs)) ^^^^^^^^^^^^^^^^^^^^^^^ leads to this guy there
> + wake_up_var(&pending->refs); > + > + wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs)); > + > + return 0; > +}
| |