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    SubjectRe: [PATCH 2/2] printk: wake up klogd in vprintk_emit
    On Sat 2018-04-14 12:01:45, Sergey Senozhatsky wrote:
    > We wake up klogd very late - only when current console_sem owner
    > is done pushing pending kernel messages to the serial/net consoles.
    > In some cases this results in lost syslog messages, because kernel
    > log buffer is a circular buffer and if we don't wakeup syslog long
    > enough there are chances that logbuf simply will wrap around.
    >
    > The patch moves the klog wake up call to vprintk_emit(), which is
    > the only legit way for a kernel message to appear in the logbuf,
    > right before we attempt to grab the console_sem (possibly spinning
    > on it waiting for the hand off) and call console drivers.
    >
    > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
    > ---
    > kernel/printk/printk.c | 14 ++------------
    > 1 file changed, 2 insertions(+), 12 deletions(-)
    >
    > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
    > index 2f4af216bd6e..86f0b337cbf6 100644
    > --- a/kernel/printk/printk.c
    > +++ b/kernel/printk/printk.c
    > @@ -1888,6 +1888,7 @@ asmlinkage int vprintk_emit(int facility, int level,
    >
    > printed_len = log_output(facility, level, lflags, dict, dictlen, text, text_len);
    >
    > + wake_up_klogd();
    > logbuf_unlock_irqrestore(flags);

    The change makes perfect sense and I am fine with the idea. I just
    wonder if there is a strong reason to do the wake_up before
    releasing the logbuf_lock. It makes an assumption that it needs
    to be synchronized by logbuf_lock.

    In fact, I would feel more comfortable if we move this to the end
    of vprintk_emit() right before return printk_len. This will be
    more close to the current behavior (console first). But it will
    still wakeup klogd much earlier and regularly if there is
    a flood of messages.

    Best Regards,
    Petr

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