From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Petr Mladek <pmladek@suse.com>, Tejun Heo <tj@kernel.org>,
akpm@linux-foundation.org, linux-mm@kvack.org,
Cong Wang <xiyou.wangcong@gmail.com>,
Dave Hansen <dave.hansen@intel.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
Vlastimil Babka <vbabka@suse.cz>,
Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Jan Kara <jack@suse.cz>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
rostedt@home.goodmis.org, Byungchul Park <byungchul.park@lge.com>,
Pavel Machek <pavel@ucw.cz>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup
Date: Wed, 24 Jan 2018 01:01:53 +0900 [thread overview]
Message-ID: <20180123160153.GC429@tigerII.localdomain> (raw)
In-Reply-To: <20180123104121.2ef96d81@gandalf.local.home>
On (01/23/18 10:41), Steven Rostedt wrote:
[..]
> We can have more. But if printk is causing printks, that's a major bug.
> And work queues are not going to fix it, it will just spread out the
> pain. Have it be 100 printks, it needs to be fixed if it is happening.
> And having all printks just generate more printks is not helpful. Even
> if we slow them down. They will still never end.
Dropping the messages is not the solution either. The original bug report
report was - this "locks up my kernel". That's it. That's all people asked
us to solve.
With WQ we don't lockup the kernel, because we flush printk_safe in
preemptible context. And people are very much expected to fix the
misbehaving consoles. But that should not be printk_safe problem.
> A printk causing a printk is a special case, and we need to just show
> enough to let the user know that its happening, and why printks are
> being throttled. Yes, we may lose data, but if every printk that goes
> out causes another printk, then there's going to be so much noise that
> we wont know what other things went wrong. Honestly, if someone showed
> me a report where the logs were filled with printks that caused
> printks, I'd stop right there and tell them that needs to be fixed
> before we do anything else. And if that recursion is happening because
> of another problem, I don't want to see the recursion printks. I want
> to see the printks that show what is causing the recursions.
I'll re-read this one tomorrow. Not quite following it.
> > The problem is - we flush printk_safe too soon and printing CPU ends up
> > in a lockup - it log_store()-s new messages while it's printing the pending
>
> No, the problem is that printks are causing more printks. Yes that will
> make flushing them soon more likely to lock up the system. But that's
> not the problem. The problem is printks causing printks.
Yes. And ignoring those printk()-s by simply dropping them does not fix
the problem by any means.
> > ones. It's fine to do so when CPU is in preemptible context. Really, we
> > should not care in printk_safe as long as we don't lockup the kernel. The
> > misbehaving console must be fixed. If CPU is not in preemptible context then
> > we do lockup the kernel. Because we flush printk_safe regardless of the
> > current CPU context. If we will flush printk_safe via WQ then we automatically
>
> And if we can throttle recursive printks, then we should be able to
> stop that from happening.
pintk_safe was designed to be recursive. It was never designed to be
used to troubleshoot or debug consoles. But it was designed to be
recursive - because that's the sort of the problems it was meant to
handle: recursive printks that would otherwise deadlock us. That's why
we have it in the first place.
> > add this "OK! The CPU is preemptible, we can log_store(), it's totally OK, we
> > will not lockup it up." thing. Yes, we fill up the logbuf with probably needed
> > and appreciated or unneeded messages. But we should not care in printk_safe.
> > We don't lockup the kernel... And the misbehaving console must be fixed.
>
> I agree.
Good.
> > I disagree with "If we are having issues with irq_work, we are going to have
> > issues with a work queue". There is a tremendous difference between irq_work
> > on that CPU and queue_work_on(smp_proessor_id()). One does not care about CPU
> > context, the other one does.
>
> But switching to work queue does not address the underlining problem
> that printks are causing more printks.
The only way to address those problems is to fix the console. That's the only.
But that's not what I'm doing with my proposal. I fix the lockup scenario, the
only reported problem so far. Whilst also keeping printk_safe around.
-ss
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next prev parent reply other threads:[~2018-01-23 16:01 UTC|newest]
Thread overview: 140+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-10 13:24 [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Petr Mladek
2018-01-10 13:24 ` [PATCH v5 1/2] printk: Add console owner and waiter logic to load balance console writes Petr Mladek
2018-01-10 16:50 ` Steven Rostedt
2018-01-12 16:54 ` Steven Rostedt
2018-01-12 17:11 ` Steven Rostedt
2018-01-17 19:13 ` Rasmus Villemoes
2018-01-17 19:33 ` Steven Rostedt
2018-01-19 9:51 ` Sergey Senozhatsky
2018-01-18 22:03 ` Pavel Machek
2018-01-19 0:20 ` Steven Rostedt
2018-01-17 2:19 ` Byungchul Park
2018-01-17 4:54 ` Byungchul Park
2018-01-17 7:34 ` Byungchul Park
2018-01-17 12:04 ` Petr Mladek
2018-01-18 1:53 ` Byungchul Park
2018-01-18 1:57 ` Byungchul Park
2018-01-18 2:19 ` Steven Rostedt
2018-01-18 4:01 ` Byungchul Park
2018-01-18 15:21 ` Steven Rostedt
2018-01-19 2:37 ` Byungchul Park
2018-01-19 3:27 ` Steven Rostedt
2018-01-22 2:31 ` Byungchul Park
2018-01-10 13:24 ` [PATCH v5 2/2] printk: Hide console waiter logic into helpers Petr Mladek
2018-01-10 17:52 ` Steven Rostedt
2018-01-11 12:03 ` Petr Mladek
2018-01-12 15:37 ` Steven Rostedt
2018-01-12 16:08 ` Petr Mladek
2018-01-12 16:36 ` Steven Rostedt
2018-01-15 16:08 ` Petr Mladek
2018-01-16 5:05 ` Sergey Senozhatsky
2018-01-10 14:05 ` [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Tejun Heo
2018-01-10 16:29 ` Petr Mladek
2018-01-10 17:02 ` Tejun Heo
2018-01-10 18:21 ` Peter Zijlstra
2018-01-10 18:30 ` Tejun Heo
2018-01-10 18:41 ` Peter Zijlstra
2018-01-10 19:05 ` Tejun Heo
2018-01-11 5:15 ` Sergey Senozhatsky
2018-01-10 18:22 ` Steven Rostedt
2018-01-10 18:36 ` Tejun Heo
2018-01-10 18:40 ` Mathieu Desnoyers
2018-01-11 7:36 ` Sergey Senozhatsky
2018-01-11 11:24 ` Petr Mladek
2018-01-11 13:19 ` Sergey Senozhatsky
2018-01-24 9:36 ` Peter Zijlstra
2018-01-24 18:46 ` Tejun Heo
2018-05-09 8:58 ` Sergey Senozhatsky
2018-01-10 18:54 ` Steven Rostedt
2018-01-11 5:10 ` Sergey Senozhatsky
2018-01-10 18:05 ` Steven Rostedt
2018-01-10 18:12 ` Tejun Heo
2018-01-10 18:14 ` Tejun Heo
2018-01-10 18:45 ` Steven Rostedt
2018-01-10 18:41 ` Steven Rostedt
2018-01-10 18:57 ` Tejun Heo
2018-01-10 19:17 ` Steven Rostedt
2018-01-10 19:34 ` Tejun Heo
2018-01-10 19:44 ` Steven Rostedt
2018-01-10 22:44 ` Tejun Heo
2018-01-11 5:35 ` Sergey Senozhatsky
2018-01-11 4:58 ` Sergey Senozhatsky
2018-01-11 9:34 ` Petr Mladek
2018-01-11 10:38 ` Sergey Senozhatsky
2018-01-11 11:50 ` Petr Mladek
2018-01-11 16:29 ` Steven Rostedt
2018-01-12 1:30 ` Steven Rostedt
2018-01-12 2:55 ` Steven Rostedt
2018-01-12 4:20 ` Steven Rostedt
2018-01-16 19:44 ` Tejun Heo
2018-01-17 9:12 ` Petr Mladek
2018-01-17 15:15 ` Tejun Heo
2018-01-17 17:12 ` Steven Rostedt
2018-01-17 18:42 ` Steven Rostedt
2018-01-19 18:20 ` Steven Rostedt
2018-01-20 7:14 ` Sergey Senozhatsky
2018-01-20 15:49 ` Steven Rostedt
2018-01-21 14:15 ` Sergey Senozhatsky
2018-01-21 21:04 ` Steven Rostedt
2018-01-22 8:56 ` Sergey Senozhatsky
2018-01-22 10:28 ` Sergey Senozhatsky
2018-01-22 10:36 ` Sergey Senozhatsky
2018-01-23 6:40 ` Sergey Senozhatsky
2018-01-23 7:05 ` Sergey Senozhatsky
2018-01-23 7:31 ` Sergey Senozhatsky
2018-01-23 14:56 ` Steven Rostedt
2018-01-23 15:21 ` Sergey Senozhatsky
2018-01-23 15:41 ` Steven Rostedt
2018-01-23 15:43 ` Tejun Heo
2018-01-23 16:12 ` Sergey Senozhatsky
2018-01-23 16:13 ` Steven Rostedt
2018-01-23 17:21 ` Tejun Heo
2018-04-23 5:35 ` Sergey Senozhatsky
2018-01-23 16:01 ` Sergey Senozhatsky [this message]
2018-01-23 16:24 ` Steven Rostedt
2018-01-24 2:11 ` Sergey Senozhatsky
2018-01-24 2:52 ` Steven Rostedt
2018-01-24 4:44 ` Sergey Senozhatsky
2018-01-23 17:22 ` Tejun Heo
2018-01-20 12:19 ` Tejun Heo
2018-01-20 14:51 ` Steven Rostedt
2018-01-17 20:05 ` Tejun Heo
2018-01-18 5:43 ` Sergey Senozhatsky
2018-01-18 11:51 ` Petr Mladek
2018-01-18 5:42 ` Sergey Senozhatsky
2018-01-12 3:12 ` Sergey Senozhatsky
2018-01-12 2:56 ` Sergey Senozhatsky
2018-01-12 3:21 ` Steven Rostedt
2018-01-12 10:05 ` Sergey Senozhatsky
2018-01-12 12:21 ` Steven Rostedt
2018-01-12 12:55 ` Petr Mladek
2018-01-13 7:31 ` Sergey Senozhatsky
2018-01-15 8:51 ` Petr Mladek
2018-01-15 9:48 ` Sergey Senozhatsky
2018-01-16 5:16 ` Sergey Senozhatsky
2018-01-16 9:08 ` Petr Mladek
2018-01-15 12:08 ` Steven Rostedt
2018-01-16 4:51 ` Sergey Senozhatsky
2018-01-13 7:28 ` Sergey Senozhatsky
2018-01-15 10:17 ` Petr Mladek
2018-01-15 11:50 ` Petr Mladek
2018-01-16 6:10 ` Sergey Senozhatsky
2018-01-16 9:36 ` Petr Mladek
2018-01-16 10:10 ` Sergey Senozhatsky
2018-01-16 16:06 ` Steven Rostedt
2018-01-16 5:23 ` Sergey Senozhatsky
2018-01-15 12:06 ` Steven Rostedt
2018-01-15 14:45 ` Petr Mladek
2018-01-16 2:23 ` Sergey Senozhatsky
2018-01-16 4:47 ` Sergey Senozhatsky
2018-01-16 10:19 ` Petr Mladek
2018-01-17 2:24 ` Sergey Senozhatsky
2018-01-16 15:45 ` Steven Rostedt
2018-01-17 2:18 ` Sergey Senozhatsky
2018-01-17 13:04 ` Petr Mladek
2018-01-17 15:24 ` Steven Rostedt
2018-01-18 4:31 ` Sergey Senozhatsky
2018-01-18 15:22 ` Steven Rostedt
2018-01-16 10:13 ` Petr Mladek
2018-01-17 6:29 ` Sergey Senozhatsky
2018-01-16 1:46 ` Sergey Senozhatsky
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