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

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Message-ID: <20180420015221.GA6397@jagdpanzerIV>
Date:   Fri, 20 Apr 2018 10:52:21 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        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 (04/19/18 12:02), Petr Mladek wrote:
> 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?

Ah. Indeed!

> "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."

Looks good. Do you want me to resend the patch?

> Otherwise, it looks nice:
> 
> Reviewed-by: Petr Mladek <pmladek@...e.com>

Thanks.

	-ss