From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: "Ahmed S. Darwish" <a.darwish@linutronix.de>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
John Ogness <john.ogness@linutronix.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Prarit Bhargava <prarit@redhat.com>,
Mark Salyzyn <salyzyn@android.com>,
Chunyan Zhang <zhang.lyra@gmail.com>,
Orson Zhai <orsonzhai@gmail.com>,
Changki Kim <changki.kim@samsung.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC 2/2] printk: Add more information about the printk caller
Date: Fri, 25 Sep 2020 09:54:00 +0900 [thread overview]
Message-ID: <20200925005400.GD541@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <20200924133850.GF29288@alley>
On (20/09/24 15:38), Petr Mladek wrote:
[..]
>
> Grrrr, I wonder why I thought that in_irq() covered also the situation
> when IRQ was disabled. It was likely my wish because disabled
> interrupts are problem for printk() because the console might
> cause a softlockup.
preempt_disable() can also trigger softlockup.
> in_irq() actually behaves like in_serving_softirq().
>
> I am confused and puzzled now. I wonder what contexts are actually
> interesting for developers. It goes back to the ideas from Sergey
> about preemption disabled, ...
Are we talking about context tracking for LOG_CONT or context on
the serial console and /dev/kmsg?
If the latter, then my 5 cents, is that something like preemptible(),
which checks
(preempt_count() == 0 && !irqs_disabled())
does not look completely unreasonable.
We had a rather OK context tracking in printk() before, but for a
completely different purpose:
console_may_schedule = !oops_in_progress &&
preemptible() &&
!rcu_preempt_depth();
We know that printk() can cause RCU stalls [0]. Tracking this part
of the context state is sort of meaningful.
Let's look at this from this POV - why do we add in_irq()/etc tracking
info? Perhaps because we want to connect the dots between printk() caller
state and watchdog reports. Do we cover all watchdogs? No, I don't think
so. RCU stalls, local_irq_disable(), preempt_disable() are not covered.
Do we have any technical reasons not to add those missing bits?
[0] https://lkml.org/lkml/2018/1/9/485
-ss
next prev parent reply other threads:[~2020-09-25 0:54 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 13:56 [RFC 0/2] printk: Add more metadata for each record Petr Mladek
2020-09-23 13:56 ` [PATCH 1/2] printk: Store all three timestamps Petr Mladek
2020-09-23 22:12 ` John Ogness
2020-09-24 1:45 ` Sergey Senozhatsky
2020-09-24 11:49 ` Petr Mladek
[not found] ` <CAJ-C09hqwOJhSXx1h40q96xhNZFXxP6dUVfjUQZpO4ZhOMZLbQ@mail.gmail.com>
2020-09-25 9:51 ` Petr Mladek
2020-09-24 0:00 ` John Ogness
2020-09-24 10:37 ` Petr Mladek
2020-09-23 13:56 ` [RFC 2/2] printk: Add more information about the printk caller Petr Mladek
2020-09-24 1:40 ` Sergey Senozhatsky
2020-09-24 11:58 ` Petr Mladek
2020-09-24 2:17 ` Sergey Senozhatsky
2020-09-24 8:23 ` John Ogness
2020-09-24 13:26 ` Petr Mladek
2020-09-24 13:06 ` Petr Mladek
2020-09-24 4:24 ` Ahmed S. Darwish
2020-09-24 12:53 ` Petr Mladek
2020-09-24 13:38 ` Petr Mladek
2020-09-25 0:54 ` Sergey Senozhatsky [this message]
2020-09-25 10:20 ` Petr Mladek
2020-10-21 11:48 ` 김창기
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