Messages in this thread | | | Date | Tue, 10 Mar 2015 13:37:40 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/3] locking: ww_mutex: Allow to use rt_mutex instead of mutex for the baselock |
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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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