Messages in this thread | | | Date | Thu, 31 Jan 2013 13:46:25 +0100 | From | Jan Kara <> | Subject | Re: [PATCH] printk: Avoid softlockups in console_unlock() |
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On Wed 30-01-13 16:08:27, Andrew Morton wrote: > On Tue, 29 Jan 2013 15:54:24 +0100 > Jan Kara <jack@suse.cz> wrote: > > > > So I was testing the attached patch which does what we discussed. The bad > > > news is I was able to trigger a situation (twice) when suddently sda > > > disappeared and thus all IO requests failed with EIO. There is no trace of > > > what's happened in the kernel log. I'm guessing that disabled interrupts on > > > the printing CPU caused scsi layer to time out for some request and fail the > > > device. So where do we go from here? > > Andrew? I guess this fell off your radar via the "hrm, strange, need to > > have a closer look later" path? > > urgh. I was hoping that if we left it long enough, one of both of us > would die :( I'm too young for this strategy to work for me :)
> I fear we will rue the day when we changed printk() to bounce some of > its work up to a kernel thread. > > > Currently I'd be inclined to return to my original solution... > > Can we make it smarter? Say, take a peek at the current > softlockup/nmi-watchdog intervals, work out how for how long we can > afford to keep interrupts disabled and then use that period and > sched_clock() to work out if we're getting into trouble? IOW, remove > the hard-wired "1000" thing which will always be too high or too low > for all situations. Yes, I also thought that making offloading more clever (so that offload doesn't happen unless we really have no choice) could make the approach more acceptable.
> Implementation-wise, that would probably end up adding a kernel-wide > function along the lines of > > /* > * Return the maximum number of nanosecond for which interrupts may be disabled > * on the current CPU > */ > u64 max_interrupt_disabled_duration(void) > { > return min(sortirq duration, nmi watchdog duration); > } OK, that sounds good. So I'll write some patch...
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
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