Hello,
On Wed 25-11-15 12:02:17, Tejun Heo wrote:
> On Wed, Nov 25, 2015 at 10:05:22AM +0100, Jan Kara wrote:
> > So did you particularly have an issue during console registration? Because
>
> Yeap, we're seeing a small ratio of machines falling head over hills
> during IPMI serial console registration. Pumping out the messages
> collected prior to registration takes too long triggering softlockup
> warning on all forty something CPUs which pile a metric ton of
> messages atop. From then on, softlockup / rcu stall warnings repeat
> themselves. Some machines recover after >10mins of doing that. The
> log is hillarious to look at afterward.
OK, then feel free to add my:
Acked-by: Jan Kara <j...@suse.com>
> > at least our customers mostly have issues during heavy use of ordinary
> > printk (e.g. during boot or when hardware gets probed) and your change
> > doesn't affect that case. That being said if you really hit a case where
>
> Hah, that must be a lot of messages being printk'd.
Yes, it is. They have ~1000 SCSI devices attached (250 disks, each over 4
paths) and similar stuff. But also doing sysrq-t on a large machine
generates enough output to kill the machine...
> > your patch helps, then I have no problem with it (you can add my Acked-by).
> >
> > At Kernel Summit I spoke with Linus and Andrew regarding printk softlockups
> > and we ended up with a decision that we decouple queueing into kernel
> > ringbuffer from the actual printing into console which would happen from
> > kthread / workqueue. Then the lockups would be solved by printing to
> > console happening from schedulable context and printk() as such being
> > independent from console speed. We only have to have some special cases
> > there for crashes so that messages get printed synchronously in that case.
>
> Yeah, we'd prolly want to make the behavior contingent on the time
> taken and so on. At any rate, even with workqueue-deferred dumping,
> this patch would still be necessary for non-preemptible kernels;
> otherwise, there's no cond_resched() in printing path right now.
Yup.
Honza
--
Jan Kara <j...@suse.com>
SUSE Labs, CR
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