From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Dmitry Safonov <dima@arista.com>
Cc: linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>, Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [RFC] printk/sysrq: Don't play with console_loglevel
Date: Tue, 28 May 2019 13:46:19 +0900 [thread overview]
Message-ID: <20190528044619.GA3429@jagdpanzerIV> (raw)
In-Reply-To: <20190528041500.GB26865@jagdpanzerIV>
On (05/28/19 13:15), Sergey Senozhatsky wrote:
> On (05/28/19 01:24), Dmitry Safonov wrote:
> [..]
> > While handling sysrq the console_loglevel is bumped to default to print
> > sysrq headers. It's done to print sysrq messages with WARNING level for
> > consumers of /proc/kmsg, though it sucks by the following reasons:
> > - changing console_loglevel may produce tons of messages (especially on
> > bloated with debug/info prints systems)
> > - it doesn't guarantee that the message will be printed as printk may
> > deffer the actual console output from buffer (see the comment near
> > printk() in kernel/printk/printk.c)
> >
> > Provide KERN_UNSUPPRESSED printk() annotation for such legacy places.
> > Make sysrq print the headers unsuppressed instead of changing
> > console_loglevel.
>
> I've been thinking about this a while ago... So what I thought back
> then was that affected paths are atomic: sysrq, irqs, NMI, etc. Well
> at leasted it seemed to be so.
Ahh.. OK, now I sort of remember why I gave up on this idea (see [1]
at the bottom, when it comes to uv_nmi_dump_state()) - printk_NMI and
printk-safe redirections.
NMI
loglevel = NEW
printk -> printk_safe_nmi
loglevel = OLD
iret
IRQ
flush printk_safe_nmi -> printk
// At this point we don't remember about
// loglevel manipulation anymore
iret
We, probably, still need some flags to pass the "this was supposed to
be an important messages" info from printk-safe to normal printk. On
the other hand, if NMI printk-s then it's something rather important,
so we probably better print it anyway and avoid suppress_message_printing()
check for messages which are coming from printk-NMI buffers. To some
extent, it's the same with printk-safe: we don't use it unless we have
a very good reason. So if there is something in printk-safe buffers
then it better end up on consoles. So, maybe, we still can use that
per-CPU printk_context thing.
[1] https://lore.kernel.org/lkml/20180601044050.GA5687@jagdpanzerIV/
-ss
next prev parent reply other threads:[~2019-05-28 4:47 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-28 0:24 [RFC] printk/sysrq: Don't play with console_loglevel Dmitry Safonov
2019-05-28 3:21 ` Tetsuo Handa
2019-05-28 4:22 ` Sergey Senozhatsky
2019-05-28 8:02 ` Tetsuo Handa
2019-05-28 8:51 ` Sergey Senozhatsky
2019-05-28 10:15 ` Tetsuo Handa
2019-05-28 13:49 ` Petr Mladek
2019-06-07 17:09 ` Pavel Machek
2019-06-08 2:45 ` Tetsuo Handa
2019-06-11 15:10 ` Petr Mladek
2019-06-12 10:06 ` Tetsuo Handa
2019-05-28 4:15 ` Sergey Senozhatsky
2019-05-28 4:46 ` Sergey Senozhatsky [this message]
2019-05-28 13:42 ` Petr Mladek
2019-05-28 14:21 ` Tetsuo Handa
2019-05-28 15:03 ` Petr Mladek
2019-05-28 15:21 ` Tetsuo Handa
2019-05-28 15:58 ` Dmitry Safonov
2019-05-31 14:11 ` Tetsuo Handa
2019-06-02 6:13 ` [RFC] printk: Introduce per context console loglevel Tetsuo Handa
2019-06-02 6:13 ` Tetsuo Handa
2019-06-06 7:59 ` Petr Mladek
2019-06-06 7:59 ` Petr Mladek
2019-06-03 6:51 ` [RFC] printk/sysrq: Don't play with console_loglevel Sergey Senozhatsky
2019-06-06 7:10 ` Petr Mladek
2019-06-12 8:36 ` Sergey Senozhatsky
2019-06-12 12:00 ` Petr Mladek
2019-06-12 14:47 ` Dmitry Safonov
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