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    SubjectRe: [RFC][PATCH 12/12 v3] x86/nmi: Perform a safe NMI stack trace on all CPUs
    On Wed, 5 Nov 2014 00:05:12 +0100 (CET)
    Jiri Kosina <jkosina@suse.cz> wrote:

    > On Tue, 4 Nov 2014, Steven Rostedt wrote:
    >
    > > From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
    > >
    > > When trigger_all_cpu_backtrace() is called on x86, it will trigger an
    > > NMI on each CPU and call show_regs(). But this can lead to a hard lock
    > > up if the NMI comes in on another printk().
    > >
    > > In order to avoid this, when the NMI triggers, it switches the printk
    > > routine for that CPU to call a NMI safe printk function that records the
    > > printk in a per_cpu seq_buf descriptor. After all NMIs have finished
    > > recording its data, the trace_seqs are printed in a safe context.

    Hmm, I need to update the change log to say seq_bufs instead of
    trace_seqs.

    > >
    > > Link: http://lkml.kernel.org/p/20140619213952.360076309@goodmis.org
    > >
    > > Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    >
    > I've been running the whole machinery that used to trigger very quickly
    > the complete hardlock of the machine (*) for the whole evening/night, and
    > it's still running flawlessly.
    >
    > Plus, as I said previously, I agree with the whole idea (given the
    > general nastiness of the problem and given the fact this simply has to be
    > fixed without pointless delays).
    >
    > I.e FWIW
    >
    > Tested-by: Jiri Kosina <jkosina@suse.cz>
    > Acked-by: Jiri Kosina <jkosina@suse.cz>
    >
    > for the whole series.

    Thanks! I'll update the commits.

    -- Steve

    >
    > (*) heavy printk() workload (**) + sysrq-l in parallel
    > (**) iptables logging every incoming packet + flood ping from another
    > machine
    >
    > Thanks,
    >



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