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    SubjectRe: PREEMPT_RT (2.6.33-rt17) disabled printk-to-console after console_init
    On Thu, 20 May 2010, Nikita V. Youshchenko wrote:

    > > > Still questions:
    > > >
    > > > 1) why does that prevent klogd from working?
    > >
    > > Patch below.
    > > ...
    > > @@ -1084,18 +1084,8 @@ void release_console_mutex(void)
    > > #endif
    > > }
    > > console_locked = 0;
    > > - raw_spin_unlock_irqrestore(&logbuf_lock, flags);
    > > mutex_unlock(&console_mutex);
    >
    > Hmm... that lock is taken inside loop body, then control goes out of loop
    > at 'break' statement, and then, if this line is deteled, lock is still
    > held at function return. Looks wrong.

    Stupid me. Yes. Drop that line.

    > > > 3) I believe that 8250 serial driver is aware of preempt-rt.
    > > > Could you please comment on my "2.6.33.2-rt13: RFC: fix serial
    > > > console" post to linux-rt-users list
    > > > (http://eeek.borgchat.net/lists/linux-rt-users/msg05569.html)
    > >
    > > While that can work due to the trylock, it can introduce massive
    > > latencies just in case some driver reports a status change or what
    > > ever.
    >
    > Isn't it better just manually disable console (with 'quiet' kernel command
    > line option) when running in production? This may be recommended in proper
    > guidelines.

    No, anything which needs extra parameters for normal operation is
    wrong as it affects users.

    Adding a "I'm debugging, I don't care" flag for developers is the
    right thing to do.

    Thanks,

    tglx



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