From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: "Sergey Senozhatsky" <sergey.senozhatsky.work@gmail.com>,
"Lech Perczak" <l.perczak@camlintechnologies.com>,
"Petr Mladek" <pmladek@suse.com>,
"Steven Rostedt" <rostedt@goodmis.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Theodore Ts'o" <tytso@mit.edu>, "Arnd Bergmann" <arnd@arndb.de>,
"Krzysztof Drobiński" <k.drobinski@camlintechnologies.com>,
"Pawel Lenkow" <p.lenkow@camlintechnologies.com>
Subject: Re: Regression in v4.19.106 breaking waking up of readers of /proc/kmsg and /dev/kmsg
Date: Fri, 28 Feb 2020 21:02:38 +0900 [thread overview]
Message-ID: <20200228120238.GC121952@google.com> (raw)
In-Reply-To: <87r1yfvzy5.fsf@linutronix.de>
On (20/02/28 10:11), John Ogness wrote:
[..]
> >> >>> My test scenario for bisecting was:
> >> >>> 1. run 'dmesg --follow' as root
> >> >>> 2. run 'echo t > /proc/sysrq-trigger'
> >> >>> 3. If trace appears in dmesg output -> good, otherwise, bad. If trace doesn't appear in output of 'dmesg --follow', re-running it will show the trace.
> >> >>>
> >> >>> I ran my tests on Debian 10.3 with configuration based directly on one from 4.19.0-8-amd64 (4.19.98-1) in Qemu.
> >> >>> I could reproduce the same issue on several boards with x86 and ARMv7 CPUs alike, with 100% reproducibility.
> >
> > This is very-very odd... Hmm.
> > Just out of curiosity, what happens if you comment out that
> > printk() entirely?
> >
> > printk_deferred() should not affect the PRINTK_PENDING_WAKEUP path.
>
> It is the printk_deferred() causing the issue. This is relatively early,
> so perhaps something is not yet properly initialized.
>
> > Either we never queue wakeup irq_work(), e.g. because
> > waitqueue_active() never lets us to do so or because `(curr_log_seq !=
> > log_next_seq)' is always zero
>
> wake_up_klogd() is called and the waitqueue (@log_wait) is
> active. irq_work_queue() is called, but the work function,
> wake_up_klogd_work_func(), is never called.
>
> Perhaps @wake_up_klogd_work gets broken somehow. I'm looking into it.
Thanks.
The interesting part here is that @wake_up_klogd_work is per-CPU. So
while I can imagine that, for instance, boot-CPU would get busted, but
not sure I see why all CPUs would experience problems. Maybe we hit
that randomness warning for every CPU during bring up? Then maybe some
more randomness-related patches need to be backported to 4.19?
-ss
next prev parent reply other threads:[~2020-02-28 12:02 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-27 11:09 Regression in v4.19.106 breaking waking up of readers of /proc/kmsg and /dev/kmsg Lech Perczak
2020-02-27 12:36 ` Greg Kroah-Hartman
2020-02-27 12:39 ` Lech Perczak
2020-02-27 14:08 ` Lech Perczak
2020-02-28 3:13 ` Sergey Senozhatsky
2020-02-28 9:11 ` John Ogness
2020-02-28 12:02 ` Sergey Senozhatsky [this message]
2020-02-28 10:04 ` Petr Mladek
2020-02-28 10:58 ` Greg Kroah-Hartman
2020-02-28 11:32 ` Petr Mladek
2020-02-28 11:39 ` Greg Kroah-Hartman
2020-02-28 13:02 ` Petr Mladek
2020-02-28 13:41 ` Greg Kroah-Hartman
2020-02-28 20:53 ` Theodore Y. Ts'o
2020-02-29 3:32 ` Sergey Senozhatsky
2020-02-29 4:08 ` Sergey Senozhatsky
2020-02-29 23:47 ` Steven Rostedt
2020-03-01 5:22 ` Sergey Senozhatsky
2020-03-02 9:49 ` Petr Mladek
2020-03-02 9:59 ` Sergey Senozhatsky
2020-02-28 11:49 ` Sergey Senozhatsky
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