From: John Ogness <john.ogness@linutronix.de>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: "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 10:11:30 +0100 [thread overview]
Message-ID: <87r1yfvzy5.fsf@linutronix.de> (raw)
In-Reply-To: <20200228031306.GO122464@google.com> (Sergey Senozhatsky's message of "Fri, 28 Feb 2020 12:13:06 +0900")
On 2020-02-28, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
> Cc-ing Petr, Steven, John
Thanks.
> https://lore.kernel.org/lkml/e9358218-98c9-2866-8f40-5955d093dc1b@camlintechnologies.com
>
> On (20/02/27 14:08), Lech Perczak 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.
John Ogness
next prev parent reply other threads:[~2020-02-28 9:11 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 [this message]
2020-02-28 12:02 ` Sergey Senozhatsky
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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