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    SubjectRE: [linux-pm] Additional fix : (was [v2]printk: fix delayed messages from CPU hotplug events)
    Andrew,
    > -----Original Message-----
    > From: linux-pm-bounces@lists.linux-foundation.org [mailto:linux-pm-
    > bounces@lists.linux-foundation.org] On Behalf Of Shilimkar, Santosh
    > Sent: Thursday, July 01, 2010 9:58 AM
    > To: Kevin Cernekee; linux-pm@lists.linux-foundation.org
    > Cc: King - ARM Linux; linux-kernel@vger.kernel.org; Russell@smtp1.linux-
    > foundation.org
    > Subject: Re: [linux-pm] Additional fix : (was [v2]printk: fix delayed
    > messages from CPU hotplug events)
    >
    > (Adding linux-pm@lists.linux-foundation.org)
    >
    > > -----Original Message-----
    > > From: Shilimkar, Santosh
    > > Sent: Tuesday, June 29, 2010 2:22 PM
    > > To: 'Kevin Cernekee'
    > > Cc: linux-kernel@vger.kernel.org; Russell King - ARM Linux
    > > Subject: Additional fix : (was [v2]printk: fix delayed messages from CPU
    > > hotplug events)
    > >
    > > Hi,
    > >
    > > I have faced similar issue as what is being described in below with
    > > latest kernel.
    > >
    > > ------------------------------------------------
    > > https://patchwork.kernel.org/patch/103347/
    > >
    > > 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:
    > >
    > > http://lkml.org/lkml/2010/5/30/4
    > >
    > > 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();
    > > }
    > >
    > >
    Haven't seen any comment on the original patch and this additional fix.
    Patch as such is straight forward and useful. Can you please have a look
    at it, if its ok.

    Regards,
    Santosh


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