From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky@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
Subject: Re: [PATCH 2/2] printk: wake up klogd in vprintk_emit
Date: Wed, 18 Apr 2018 16:04:09 +0200 [thread overview]
Message-ID: <20180418140409.6hvkbip4skfs4x7y@pathway.suse.cz> (raw)
In-Reply-To: <20180414030145.26304-1-sergey.senozhatsky@gmail.com>
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
next prev parent reply other threads:[~2018-04-18 14:04 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-14 3:01 [PATCH 2/2] printk: wake up klogd in vprintk_emit Sergey Senozhatsky
2018-04-18 14:04 ` Petr Mladek [this message]
2018-04-19 1:23 ` Sergey Senozhatsky
2018-04-19 9:54 ` Petr Mladek
2018-04-18 14:29 ` Steven Rostedt
2018-04-18 15:02 ` Petr Mladek
2018-04-18 15:10 ` Steven Rostedt
2018-04-19 1:17 ` Sergey Senozhatsky
2018-04-19 1:42 ` [PATCHv2] " Sergey Senozhatsky
2018-04-19 10:02 ` Petr Mladek
2018-04-20 1:52 ` Sergey Senozhatsky
2018-04-20 8:18 ` Petr Mladek
2018-04-25 13:23 ` Petr Mladek
2018-04-26 1:44 ` Sergey Senozhatsky
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