From: Lech Perczak <l.perczak@camlintechnologies.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "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: Thu, 27 Feb 2020 12:39:34 +0000 [thread overview]
Message-ID: <42d3ce5c-5ffe-8e17-32a3-5127a6c7c7d8@camlintechnologies.com> (raw)
In-Reply-To: <20200227123633.GB962932@kroah.com>
W dniu 27.02.2020 o 13:36, Greg Kroah-Hartman pisze:
> On Thu, Feb 27, 2020 at 11:09:49AM +0000, Lech Perczak wrote:
>> Hello,
>>
>> After upgrading kernel on our boards from v4.19.105 to v4.19.106 we found out that syslog fails to read the messages after ones read initially after opening /proc/kmsg just after booting.
>> I also found out, that output of 'dmesg --follow' also doesn't react on new printks appearing for whatever reason - to read new messages, reopening /proc/kmsg or /dev/kmsg was needed.
>> I bisected this down to commit 15341b1dd409749fa5625e4b632013b6ba81609b ("char/random: silence a lockdep splat with printk()"), and reverting it on top of v4.19.106 restored correct behaviour.
> That is really really odd.
Very odd it is indeed.
>
>> 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.
>>
>> I haven't yet digged into why exactly this commit breaks notifications for readers of /proc/kmsg and /dev/kmsg, but as reverting it fixed the issue, I'm pretty sure this is the one. It is possible that the same happened in 5.4 line, bu I hadn't had a chance to test this as well yet.
> I can revert this, but it feels like there is something else going wrong
> here. Can you try the 5.4 tree to see if that too has your same
> problem?
Yes, I'll check it in a short while.
>
> thanks,
>
> greg k-h
--
Pozdrawiam/With kind regards,
Lech Perczak
Sr. Software Engineer
Camlin Technologies Poland Limited Sp. z o.o.
next prev parent reply other threads:[~2020-02-27 12:39 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 [this message]
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
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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