From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Sergey Senozhatsky" <sergey.senozhatsky.work@gmail.com>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
"Petr Mladek" <pmladek@suse.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Lech Perczak" <l.perczak@camlintechnologies.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Arnd Bergmann" <arnd@arndb.de>,
"Krzysztof Drobiński" <k.drobinski@camlintechnologies.com>,
"Pawel Lenkow" <p.lenkow@camlintechnologies.com>,
"John Ogness" <john.ogness@linutronix.de>,
"Tejun Heo" <tj@kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>
Subject: Re: Regression in v4.19.106 breaking waking up of readers of /proc/kmsg and /dev/kmsg
Date: Sun, 1 Mar 2020 14:22:19 +0900 [thread overview]
Message-ID: <20200301052219.GA83612@google.com> (raw)
In-Reply-To: <20200229184719.714dee74@oasis.local.home>
On (20/02/29 18:47), Steven Rostedt wrote:
[..]
> > > What do folks think?
> >
> > Well, my 5 cents, there is nothing that prevents "too-early"
> > printk_deferred() calls in the future. From that POV I'd probably
> > prefer to "forbid" printk_deffered() to touch per-CPU deferred
> > machinery until it's not "too early" anymore. Similar to what we
> > do in printk_safe::queue_flush_work().
>
> I agree that printk_deferred() should handle being called too early.
> But the issue is with per_cpu variables correct? Not the irq_work?
Correct. printk_deferred() and printk_safe()/printk_nmi() irq_works
are per-CPU. We use "a special" flag in printk_safe()/printk_nmi() to
tell if it's too early to modify per-CPU irq_work or not.
I believe that we need to use that flag for all printk-safe/nmi
per-CPU data, including buffers, not only for irq_work. Just in
case if printk_safe or printk_nmi, somehow, are being called too
early.
> We could add a flag in init/main.c after setup_per_cpu_areas() and then
> just have printk_deferred() act like a normal printk(). At that point,
> there shouldn't be an issue in calling printk() directly, is there?
Sure, this will work. I believe we introduced a "work around" approach
in printk-safe because noone would ACK a global init/main.c flag for
printk(). If we can land a "per_cpu_areas_ready" flag (I've some doubts
here), then yes (!), let's use it and let's remove printk-safe workaround.
-ss
next prev parent reply other threads:[~2020-03-01 5:22 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
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 [this message]
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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