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    SubjectRe: Additional fix : (was [v2]printk: fix delayed messages from CPU hotplug events)
    On Tue, 29 Jun 2010 14:22:26 +0530
    "Shilimkar, Santosh" <> wrote:

    > Hi,
    > I have faced similar issue as what is being described in below with
    > latest kernel.
    > ------------------------------------------------
    > When a secondary CPU is being brought up, it is not uncommon for
    > printk() to be invoked when cpu_online(smp_processor_id()) == 0. The
    > case that I witnessed personally was on MIPS:
    > If (can_use_console() == 0), printk() will spool its output to log_buf
    > and it will be visible in "dmesg", but that output will NOT be echoed to
    > the console until somebody calls release_console_sem() from a CPU that
    > is online. Therefore, the boot time messages from the new CPU can get
    > stuck in "limbo" for a long time, and might suddenly appear on the
    > screen when a completely unrelated event (e.g. "eth0: link is down")
    > occurs.
    > This patch modifies the console code so that any pending messages are
    > automatically flushed out to the console whenever a CPU hotplug
    > operation completes successfully or aborts.
    > -----------------------------------------------
    > Above patch fixes only half of the problem. I mean the cpu online
    > path prints are coming on the console.
    > But similar problem also exist if there are prints in the cpu offline
    > path. I got that fixed by adding below patch on top of you patch.
    > diff --git a/kernel/printk.c b/kernel/printk.c
    > index d370b74..f4d7352 100644
    > --- a/kernel/printk.c
    > +++ b/kernel/printk.c
    > @@ -982,6 +982,9 @@ static int __cpuinit console_cpu_notify(struct notifier_bloc
    > switch (action) {
    > case CPU_ONLINE:
    > case CPU_UP_CANCELED:
    > + case CPU_DEAD:
    > + case CPU_DYING:
    > + case CPU_DOWN_FAILED:
    > if (try_acquire_console_sem() == 0)
    > release_console_sem();
    > }

    The patch lacked a suitable title. I called it "console: flush log
    messages for more cpu-hotplug events".

    The patch lacks a Signed-off-by:. Please send one.

    The patch has its tabs replaced with spaces. I fixed that. Please
    reconfigure your email client for next time.

    The code which is being patch has changed. It now does


    so the code may no longer work - perhaps it now deadlocks (unlikely).
    Please retest?

    Finally, I don't understand the patch :( Who is sending out CPU_DEAD,
    CPU_DYING or CPU_DOWN_FAILED events during kernel boot? I'd have
    thought that those events simply aren't occurring, and that the patch
    has no effect. Confused - please explain further.

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