[Mesa-dev] [PATCH 07/10] util/u_queue: add an option to resize the queue when it's full

[Grazvydas Ignotas]

On Tue, Jul 11, 2017 at 12:21 AM, Marek Olšák <maraeo at gmail.com> wrote:
> From: Marek Olšák <marek.olsak at amd.com>
>
> Consider the following situation:
>   mtx_lock(mutex);
>   do_something();
>   util_queue_add_job(...);
>   mtx_unlock(mutex);
>
> If the queue is full, util_queue_add_job will wait for a free slot.
> If the job which is currently being executed tries to lock the mutex,
> it will be stuck forever, because util_queue_add_job is stuck.
>
> The deadlock can be trivially resolved by increasing the queue size
> (reallocating the queue) in util_queue_add_job if the queue is full.
> Then util_queue_add_job becomes wait-free.
>
> radeonsi will use it.

Can't this cause the queue to grow uncontrollably, like on GPU hangs,
making already difficult to debug situations worse? Perhaps
util_queue_add_job() could have a non-blocking-fail option and the
caller could then retry after releasing the mutex for a bit.

Gražvydas