On Fri, Feb 27, 2015 at 05:57:08PM +0100, Sebastian Andrzej Siewior wrote:
> +static int __sched __mutex_lock_check_stamp(struct rt_mutex *lock,
> + struct ww_acquire_ctx *ctx)
> +{
> +#ifdef CONFIG_WW_MUTEX_RTMUTEX
> + struct ww_mutex *ww = container_of(lock, struct ww_mutex, base.lock);
> + struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx);
> +
> + if (!hold_ctx)
> + return 0;
> +
> + if (unlikely(ctx == hold_ctx))
> + return -EALREADY;
> +
> + if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
> + (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
> +#ifdef CONFIG_DEBUG_MUTEXES
> + DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
> + ctx->contending_lock = ww;
> +#endif
> + return -EDEADLK;
> + }
> +#endif
> + return 0;
> +}
So IIRC this is the function that checks who gets wounded (and gets to
do the whole retry thing), right?
So for the RT case, I think we should extend it to not (primarily) be a
FIFO thing, but also consider the priority of the tasks involved.
Maybe a little something like:
if (hold_ctx->task->prio < ctx->task->prio)
return -EDEADLOCK;
before the timestamp check; although I suppose we should also add a
deadline test in case both prios are -1.
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