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From: Petr Mladek <pmladek@suse.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] printk: wake up klogd in vprintk_emit
Date: Wed, 18 Apr 2018 17:02:14 +0200	[thread overview]
Message-ID: <20180418150214.z7oyughldrktj6e4@pathway.suse.cz> (raw)
In-Reply-To: <20180418102943.5aa0ffc4@gandalf.local.home>

On Wed 2018-04-18 10:29:43, Steven Rostedt wrote:
> On Sat, 14 Apr 2018 12:01:45 +0900
> Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:
> 
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -1888,6 +1888,7 @@ asmlinkage int vprintk_emit(int facility, int level,
> >  
> >  	printed_len = log_output(facility, level, lflags, dict, dictlen, text, text_len);
> >  
> > +	wake_up_klogd();
> >  	logbuf_unlock_irqrestore(flags);
> 
> You can't do this, because the scheduler can call printk_deferred()
> with the rq lock held, and printk_deferred() will grab the logbuf lock.
> 
> Calling wake_up_klogd() will grab the rq lock and give us a A-B<->B-A
> locking order.

wake_up_klogd() uses the lockless irq_work_queue(). So it is actually
safe.

But the name is confusing. We should rename it.

Best Regards,
Petr

  reply	other threads:[~2018-04-18 15:02 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-14  3:01 [PATCH 2/2] printk: wake up klogd in vprintk_emit Sergey Senozhatsky
2018-04-18 14:04 ` Petr Mladek
2018-04-19  1:23   ` Sergey Senozhatsky
2018-04-19  9:54     ` Petr Mladek
2018-04-18 14:29 ` Steven Rostedt
2018-04-18 15:02   ` Petr Mladek [this message]
2018-04-18 15:10     ` Steven Rostedt
2018-04-19  1:17       ` Sergey Senozhatsky
2018-04-19  1:42 ` [PATCHv2] " Sergey Senozhatsky
2018-04-19 10:02   ` Petr Mladek
2018-04-20  1:52     ` Sergey Senozhatsky
2018-04-20  8:18       ` Petr Mladek
2018-04-25 13:23       ` Petr Mladek
2018-04-26  1:44         ` Sergey Senozhatsky

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