Messages in this thread | | | Date | Mon, 21 Mar 2016 17:47:43 +0900 | From | Byungchul Park <> | Subject | Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async |
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On Mon, Mar 21, 2016 at 05:07:51PM +0900, Byungchul Park wrote: > On Mon, Mar 21, 2016 at 04:35:07PM +0900, Sergey Senozhatsky wrote: > > On (03/21/16 09:56), Byungchul Park wrote: > > > > > > + if (!sync_print) { > > > > > > + if (in_sched) { > > > > > > + /* > > > > > > + * @in_sched messages may come too early, when we don't > > > > > > + * yet have @printk_kthread. We can't print deferred > > > > > > + * messages directly, because this may deadlock, route > > > > > > + * them via IRQ context. > > > > > > + */ > > > > > > + __this_cpu_or(printk_pending, > > > > > > + PRINTK_PENDING_OUTPUT); > > > > > > + irq_work_queue(this_cpu_ptr(&wake_up_klogd_work)); > > > > > > + } else if (printk_kthread && !in_panic) { > > > > > > + /* Offload printing to a schedulable context. */ > > > > > > + wake_up_process(printk_kthread); > > > > > > > > > > It will not print the "lockup suspected" message at all, for e.g. rq->lock, > > > > > p->pi_lock and any locks which are used within wake_up_process(). > > > > > > > > this will switch to old SYNC printk() mode should such a lockup ever > > > > happen, which is a giant advantage over any other implementation; doing > > > > wake_up_process() within the 'we can detect recursive printk() here' > > > > gives us better control. > > > > > > > > why > > > > printk()->IRQ->wake_up_process()->spin_dump()->printk()->IRQ->wake_up_process()->spin_dump()->printk()->IRQ... > > > > is better? > > > > > > What is IRQ? > > > > this is how printk() can print the messages in async mode apart from > > direct and wake_up_process() in vprintk_emit(). > > Do you mean IRQ work? > > Is there any reason why you don't put the wake_up_process() out of the > critical section with my suggestion, even though it can solve the infinite > recuresion you worried about?
Just to be sure, whether you take my suggestion or not is not important. I just suggested it in this thread since it can solve what you worried about. That's all. I can post it in another thread though. Why don't you consider it so that yours don't miss any printk message? Do you think there are any problems in my suggestion?
> > > > > -ss > > > > > > > Furtheremore, any printk() within wake_up_process() cannot work at all, as > > > > > well. > > > > > > > > there is printk_deferred() which has LOGLEVEL_SCHED and which must be used > > > > in sched functions. > > > > > > It would be good for all scheduler code to use the printk_deferred() as you > > > said, but it's not true yet. > > > > > > > > > > > -ss > > >
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