linux-kernel - Re: [PATCHv2] printk: wake up klogd in vprintk

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Message-ID: <20180419100248.rflodqcvpvnve5vl@pathway.suse.cz>
Date:   Thu, 19 Apr 2018 12:02:48 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCHv2] printk: wake up klogd in vprintk_emit

On Thu 2018-04-19 10:42:50, 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.

The last two lines need an update. What about?

"right after the attempt to handle consoles. As a result, klog
will get waken either after flushing the new message to consoles
or immediately when consoles are still busy with older messages."

Otherwise, it looks nice:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr