linux-kernel - Re: consoles: was: [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog

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Date:   Wed, 9 Dec 2020 05:51:37 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: consoles: was: [PATCH next v2 3/3] printk: remove logbuf_lock,
 add syslog_lock

On (20/12/07 10:50), Petr Mladek wrote:
[..]
> > and then some call into the scheduler
> > (or other kernel core functions) under semaphore's spin_lock.
> > For instance
> > 
> > 	up()
> > 	 raw_spin_lock_irqsave(&sem->lock)
> > 	   __up()
> > 	     wake_up_process()
> > 	       try_to_wake_up()
> 
> This problem is partly solved by printk_deferred(). In each
> case, printk_safe() does not help here.

printk_deferred() has never been used in all the critical code paths.
So I think printk_safe does help here; it takes care of all the
remaining cases, that are not "partly solved by printk_deferred()".

> I still do _not_ see a reason to keep printk_safe()!

Not sure I'm following, sorry. To put it simply - we better keep
printk_safe until "new recursion prevention" >= printk_safe().
In this patch set "new recursion prevention" < printk_safe().

	-ss