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    SubjectRe: frequent lockups in 3.18rc4
    On Sun, Dec 07, 2014 at 09:58:14AM -0500, Sasha Levin wrote:
    > On 12/05/2014 01:15 PM, Linus Torvalds wrote:
    > > On Fri, Dec 5, 2014 at 7:03 AM, Sasha Levin <sasha.levin@oracle.com> wrote:
    > >>
    > >> Yes, it's going to a serial line, but it's only about 100 lines/second on
    > >> average. I wouldn't expect it to cause anything to hang!
    > >
    > > A regular 16650 serial chip? Running at 115kbps, I assume? So that's
    > > about 11kB/s.
    > >
    > > And the serial console is polling, since it can't sleep or depend on interrupts.
    > >
    > > At a average line length of what, 40 characters? At less than 300
    > > lines/s, you'd be using up 100% of one CPU. And since the printouts
    > > are serialized, that would be all other CPU's too..
    > >
    > > 100 lines/s _average_ means that I can easily see it be 300lines/s for a while.
    > >
    > > So yeah. The serial console is simply not designed to handle
    > > continuous output. It's for the "occasional" stuff.
    > >
    > > The fact that your rcu lockups go away when you make the fault
    > > injection be quiet makes me really suspect this is related.
    >
    > The lockups themselves "go away", but looking closer at the log
    > without those extra prints, I'm seeing:
    >
    > [ 1458.700070] INFO: rcu_preempt detected stalls on CPUs/tasks:
    > [ 1458.700133] (detected by 19, t=30502 jiffies, g=12293, c=12292, q=0)
    > [ 1458.702764] INFO: Stall ended before state dump start
    >
    > Quite often.
    >
    > Maybe the extra prints were just a catalyst?

    Is anything else being printed about the time that these message show
    up? Or is this the only output for the 40,000 jiffies preceding this
    message?

    Thanx, Paul



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