linux-kernel - Re: [RFC][PATCHv3 2/5] printk: introduce printing kernel thread

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Message-ID: <20170704065351.GA437@jagdpanzerIV.localdomain>
Date:   Tue, 4 Jul 2017 15:53:51 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>,
        Andreas Mohr <andi@...as.de>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCHv3 2/5] printk: introduce printing kernel thread

On (07/04/17 14:26), Sergey Senozhatsky wrote:
[..]
> not sure if we can properly throttle printk in all of the cases.
> we know that console_sem is locked, but we don't know what for.
> is CPU that owns the console_sem is now in console_unlock() or
> somewhere in fbcon, or anywhere else. we probably need not to
> throttle printk() if we know that console_sem is already locked
> by this_cpu and we simply call printk either from IRQ that
> preempted console_unlock() on this_cpu or recursive printk from
> console_unlock()... and so on.

which is hard to do, given that console_unlock() can schedule with
console_sem locked. so CPU number won't do the trick. unless we will
forbid preemption in console_unlock()... we sort of need to do it.

	-ss