linux-kernel - Re: [GIT PULL] printk: Support for full dynticks mode

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Message-ID: <CAFTL4hxHEknUfv0rt73Tb0YAUrypuGJArvCw4wmEPp_8PF_b0A@mail.gmail.com>
Date:	Tue, 5 Feb 2013 02:37:54 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [GIT PULL] printk: Support for full dynticks mode

2013/2/5 Andrew Morton <akpm@...ux-foundation.org>:
> On Tue,  5 Feb 2013 01:51:18 +0100
> Frederic Weisbecker <fweisbec@...il.com> wrote:
>
>>       printk: Wake up klogd using irq_work
>
> That seems reasonable.
>
> I'm wondering if we can now remove the printk_sched() special-case.
> iirc, that was needed because wake_up(klogd) would deadlock when called
> from sched internals.  But now that wakeup is punted to the timer tick,
> perhaps this is now unnecessary?

I fear irq work doesn't change much the picture in this regard. Before
irq work, printk() and printk_sched() were already relying on the tick
(printk_tick()) to do the wake up on klogd clients. I guess that the
deadlocks referenced by Peter were about printk() internals. May be
logbuf_lock against some other scheduler lock?

>
> (Maybe there were other problems, but the 3ccf3e8306 is poor, and its
> author is unavailable.  There's a lesson there!)
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