On Mon, 2012-10-29 at 16:27 -0400, Steven Rostedt wrote:
> plain text document attachment
> (0010-nohz-cpuset-Restart-the-tick-if-printk-needs-it.patch)
> From: Frederic Weisbecker <fweis...@gmail.com>
>
> If we are in nohz adaptive mode and printk is called, the tick is
> missing to wake up the logger. We need to restart the tick when that
> happens. Do this asynchronously by issuing a tick restart self IPI
> to avoid deadlocking with the current random locking chain.
>
> Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Alessio Igor Bogani <abog...@kernel.org>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Avi Kivity <a...@redhat.com>
> Cc: Chris Metcalf <cmetc...@tilera.com>
> Cc: Christoph Lameter <c...@linux.com>
> Cc: Daniel Lezcano <daniel.lezc...@linaro.org>
> Cc: Geoff Levand <ge...@infradead.org>
> Cc: Gilad Ben Yossef <gi...@benyossef.com>
> Cc: Hakan Akkan <hakanak...@gmail.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Kevin Hilman <khil...@ti.com>
> Cc: Max Krasnyansky <m...@qualcomm.com>
> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Stephen Hemminger <shemmin...@vyatta.com>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Sven-Thorsten Dietrich <thebigcorporat...@gmail.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> ---
> kernel/printk.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/printk.c b/kernel/printk.c
> index 2d607f4..bf9048d 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -42,6 +42,7 @@
> #include <linux/notifier.h>
> #include <linux/rculist.h>
> #include <linux/poll.h>
> +#include <linux/cpuset.h>
>
> #include <asm/uaccess.h>
>
> @@ -1977,8 +1978,20 @@ int printk_needs_cpu(int cpu)
>
> void wake_up_klogd(void)
> {
> - if (waitqueue_active(&log_wait))
> + unsigned long flags;
> +
> + if (waitqueue_active(&log_wait)) {
> this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
> + /* Make it visible from any interrupt from now */
> + barrier();
> + /*
> + * It's safe to check that even if interrupts are not disabled.
Probably need to at least disable preemption. I don't see any
requirement that wake_up_klogd() needs to be called with preemption
disabled.
The this_cpu_or() doesn't care which CPU it triggers, but the enabling
of nohz does.
-- Steve
> + * If we enable nohz adaptive mode concurrently, we'll see the
> + * printk_pending value and thus keep a periodic tick behaviour.
> + */
> + if (cpuset_adaptive_nohz())
> + smp_cpuset_update_nohz(smp_processor_id());
> + }
> }
>
> static void console_cont_flush(char *text, size_t size)
--
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