Messages in this thread |  | | | Date | Wed, 21 Dec 2011 13:03:35 +0100 | | Subject | Re: printk() vs tty_io | | From | Stijn Devriendt <> |
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On Tue, Dec 13, 2011 at 8:33 PM, Peter Zijlstra <peterz@infradead.org> wrote: > Hi tty folks, > > I've been poking at reducing the constraints on printk(), like make it > work under rq->lock etc.. > > Aside from a fwd port of the patch that abuses the console_sem.lock: > https://lkml.org/lkml/2011/6/9/298 and a few other not so very pretty > patches, I ran into the following lockdep splat (using a not so very > pretty lockdep early_printk() patch): > > watchdog/0/10 is trying to acquire lock: > ((console_sem).lock){-.-...}, at: > but task is already holding lock: > (&rt_rq->rt_runtime_lock){-.-...}, at: > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #5 (&rt_rq->rt_runtime_lock){-.-...}: > -> #4 (&rq->lock){-.-.-.}: > -> #3 (&p->pi_lock){-.-.-.}: > -> #2 (&tty->write_wait){-.-...}: > -> #1 (&port_lock_key){-.-...}: > -> #0 ((console_sem).lock){-.-...}: > > It turns out that writing to a console does wakeups due to tty_io.c. > > My question is basically, is there a feasible way around doing these > wakeups from the console::write() path? Everything I thought of was > really quite horrible... and very likely would break stuff since I'm not > that well versed in the whole tty thing. >
Would it be possible to solve the problem by allowing wake-ups from inside the rq->lock? After all your hard work moving most of the wakeup work out of the ttwu() code and the ttwu-queuing for cross-cpu wakeups I believe that allowing wakeups from inside the rq->lock could be doable.
Regards, Stijn -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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