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Groups > linux.kernel > #1361572
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async |
| Date | 2016-03-21 09:10 +0100 |
| Message-ID | <rf34u-2NK-15@gated-at.bofh.it> (permalink) |
| References | (1 earlier) <reMmZ-81x-3@gated-at.bofh.it> <reVzY-65f-7@gated-at.bofh.it> <reWcG-6lC-3@gated-at.bofh.it> <reWml-6pV-1@gated-at.bofh.it> <rf2Bs-2nn-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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?
>
> -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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[RFC][PATCH v5 0/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-20 15:20 +0100
[RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-20 15:20 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-21 01:10 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-21 01:50 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-21 02:00 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-21 08:40 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-21 09:10 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-21 09:50 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-21 10:30 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Jan Kara <jack@suse.cz> - 2016-03-21 15:40 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-21 16:10 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Jan Kara <jack@suse.cz> - 2016-03-21 16:40 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-21 18:20 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-22 03:20 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-22 03:20 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-22 07:00 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Byungchul Park <byungchul.park@lge.com> - 2016-03-22 08:00 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-22 08:50 +0100
Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-03-21 10:00 +0100
[RFC][PATCH v5 2/2] printk: Make wake_up_klogd_work_func() async Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-03-20 15:20 +0100
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