linux-kernel - Re: Regression in v4.19.106 breaking waking up of readers of /proc/kmsg and /dev/kmsg

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Message-ID: <20200229184719.714dee74@oasis.local.home>
Date:   Sat, 29 Feb 2020 18:47:19 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>, Petr Mladek <pmladek@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lech Perczak <l.perczak@...lintechnologies.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Krzysztof Drobiński 
        <k.drobinski@...lintechnologies.com>,
        Pawel Lenkow <p.lenkow@...lintechnologies.com>,
        John Ogness <john.ogness@...utronix.de>,
        Tejun Heo <tj@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: Regression in v4.19.106 breaking waking up of readers of
 /proc/kmsg and /dev/kmsg

On Sat, 29 Feb 2020 12:32:53 +0900
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> 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?

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?

-- Steve