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Date: Wed, 25 Apr 2018 15:23:52 +0200
From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [PATCHv2] printk: wake up klogd in vprintk_emit
Message-ID: <20180425132352.cs22ak5jzwr2f4v4@pathway.suse.cz>
References: <20180414030145.26304-1-sergey.senozhatsky@gmail.com>
 <20180419014250.5692-1-sergey.senozhatsky@gmail.com>
 <20180419100248.rflodqcvpvnve5vl@pathway.suse.cz>
 <20180420015221.GA6397@jagdpanzerIV>
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On Fri 2018-04-20 10:52:21, Sergey Senozhatsky wrote:
> 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?

JFYI, I have updated the commit message and pushed the patch into
printk.git, for-4.18 branch.

Best Regards,
Petr