From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Andreas Mohr <andi@lisas.de>, Petr Mladek <pmladek@suse.com>
Cc: Pavel Machek <pavel@ucw.cz>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>, Jan Kara <jack@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
Eric Biederman <ebiederm@xmission.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>, Len Brown <len.brown@intel.com>,
linux-kernel@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [RFC][PATCHv2 4/8] pm: switch to printk.emergency mode in unsafe places
Date: Mon, 10 Apr 2017 23:38:17 +0900 [thread overview]
Message-ID: <20170410143817.GA457@tigerII.localdomain> (raw)
In-Reply-To: <20170410122043.GW3452@pathway.suse.cz>
On (04/10/17 14:20), Petr Mladek wrote:
[..]
> > Sergey has mentioned it already:
> > "at some point freezes user space and kernel threads".
> > Well, this is the action which is *itself* causing thoroughly disrupting consequences,
> > which I'd think thus ought to be responsible to
> > ensure *itself* that all resulting consequences actually can be dealt with properly,
> > rather than having
> > weird *completely-unrelated-dependency* crap
> > ("there happens to be some functionality called printk, and we need to bend it,
> > since we need to bend it, since otherwise it would not be bent" - ahem...)
> > leak into ("layer violation" keyword)
> > pm handling implementation specifics.
> > IOW, I would think that for any relevant kthread use in API user code,
> > such code ought to be able to
> > register kthread-API-provided callbacks (observer pattern, or whatever)
> > where the (back to current case:) printk kthread would then be able to
> > *implicitly*/*invisibly* switch the entire printk operation interface
> > (e.g. via a global interface struct) to
> > the "dumb"/"safe" fallback variant.
> > Potential interface: kthread_notify(callback_func, kthread_notification_type);
>
> Interesting idea. The power management area probably can be solved
> by the existing notifiers framework.
good idea indeed.
wish we also had kexec and sysrq notifiers :) there is a
`panic_notifier_list', but that's not exactly what we need.
[..]
> > Put differently,
> > handling preferrably ought to get consistently adapted (i.e., switched) *centrally*,
> > rather than
> > requiring weird helpers (printk_emergency_X()) at all user code sites.
>
> Note that there already all many printk/console related "hacks"
> in sensitive code paths. For example, see the use of
> pm_prepare_console(), suspend_console(), console_level.
yep. I wonder if some of those can be moved to printk pm notifiers.
but that's out of the scope of this patch set.
-ss
next prev parent reply other threads:[~2017-04-10 14:38 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-29 9:25 [RFC][PATCHv2 0/8] printk: introduce printing kernel thread Sergey Senozhatsky
2017-03-29 9:25 ` [RFC][PATCHv2 1/8] printk: move printk_pending out of per-cpu Sergey Senozhatsky
2017-03-31 13:09 ` Petr Mladek
2017-03-31 13:33 ` Peter Zijlstra
2017-04-03 11:23 ` Sergey Senozhatsky
2017-04-03 12:43 ` Petr Mladek
2017-03-29 9:25 ` [RFC][PATCHv2 2/8] printk: introduce printing kernel thread Sergey Senozhatsky
2017-04-04 9:01 ` Petr Mladek
2017-04-04 9:36 ` Sergey Senozhatsky
2017-04-06 17:14 ` Pavel Machek
2017-04-07 5:12 ` Sergey Senozhatsky
2017-04-07 7:21 ` Pavel Machek
2017-04-07 8:15 ` Sergey Senozhatsky
2017-04-07 12:06 ` Pavel Machek
2017-03-29 9:25 ` [RFC][PATCHv2 3/8] printk: offload printing from wake_up_klogd_work_func() Sergey Senozhatsky
2017-03-31 14:56 ` Petr Mladek
2017-04-04 16:15 ` Sergey Senozhatsky
2017-03-29 9:25 ` [RFC][PATCHv2 4/8] pm: switch to printk.emergency mode in unsafe places Sergey Senozhatsky
2017-03-31 15:06 ` Petr Mladek
2017-04-06 17:20 ` Pavel Machek
2017-04-09 10:59 ` Andreas Mohr
2017-04-10 12:20 ` Petr Mladek
2017-04-10 14:38 ` Sergey Senozhatsky [this message]
2017-03-29 9:25 ` [RFC][PATCHv2 5/8] sysrq: " Sergey Senozhatsky
2017-03-31 15:37 ` Petr Mladek
2017-04-01 0:04 ` Sergey Senozhatsky
2017-03-29 9:25 ` [RFC][PATCHv2 6/8] kexec: " Sergey Senozhatsky
2017-03-31 15:39 ` Petr Mladek
2017-03-29 9:25 ` [RFC][PATCHv2 7/8] printk: add printk emergency_mode parameter Sergey Senozhatsky
2017-04-03 15:29 ` Petr Mladek
2017-04-04 8:29 ` Sergey Senozhatsky
2017-03-29 9:25 ` [RFC][PATCHv2 8/8] printk: enable printk offloading Sergey Senozhatsky
2017-03-30 21:38 ` [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage kernel test robot
2017-03-31 2:35 ` Sergey Senozhatsky
2017-03-31 4:04 ` Sergey Senozhatsky
2017-03-31 6:39 ` Ye Xiaolong
2017-03-31 14:47 ` Sergey Senozhatsky
2017-03-31 15:28 ` Eric W. Biederman
2017-04-03 9:31 ` Jan Kara
2017-04-03 10:06 ` Petr Mladek
2017-04-06 17:33 ` Pavel Machek
2017-04-07 4:44 ` Sergey Senozhatsky
2017-04-07 7:15 ` Pavel Machek
2017-04-07 7:46 ` Sergey Senozhatsky
2017-04-07 8:14 ` Pavel Machek
2017-04-07 12:10 ` Sergey Senozhatsky
2017-04-07 12:44 ` Pavel Machek
2017-04-07 14:40 ` Steven Rostedt
2017-05-08 6:37 ` Sergey Senozhatsky
2017-05-17 13:13 ` Petr Mladek
2017-04-07 15:13 ` Sergey Senozhatsky
2017-04-07 15:23 ` Peter Zijlstra
2017-04-07 15:40 ` Sergey Senozhatsky
2017-04-09 18:21 ` Eric W. Biederman
2017-04-10 4:46 ` Sergey Senozhatsky
2017-04-09 10:12 ` Pavel Machek
2017-04-10 4:53 ` Sergey Senozhatsky
2017-04-10 11:54 ` Petr Mladek
2017-04-10 15:08 ` Sergey Senozhatsky
2017-04-10 18:48 ` Pavel Machek
2017-04-11 1:46 ` Sergey Senozhatsky
2017-04-11 16:19 ` Sergey Senozhatsky
2017-04-12 18:43 ` Pavel Machek
2017-04-13 4:34 ` Sergey Senozhatsky
2017-04-13 5:50 ` Sergey Senozhatsky
2017-04-13 8:19 ` Sergey Senozhatsky
2017-04-13 14:03 ` Petr Mladek
2017-04-14 4:42 ` Sergey Senozhatsky
2017-04-07 14:29 ` Steven Rostedt
2017-04-09 9:57 ` Pavel Machek
2017-04-03 10:51 ` Sergey Senozhatsky
2017-04-05 7:29 ` Ye Xiaolong
2017-04-05 8:40 ` Sergey Senozhatsky
2017-04-03 15:42 ` [RFC][PATCHv2 8/8] printk: enable printk offloading Petr Mladek
2017-04-04 13:20 ` Sergey Senozhatsky
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