linux-kernel - Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async

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Date:	Mon, 21 Mar 2016 17:51:34 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Byungchul Park <byungchul.park@....com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.com>, Petr Mladek <pmladek@...e.com>,
	Tejun Heo <tj@...nel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async

On (03/21/16 17:07), Byungchul Park wrote:
[..]
> > > > > It will not print the "lockup suspected" message at all, for e.g. rq->lock,
> > > > > p->pi_lock and any locks which are used within wake_up_process().
> > > > 
> > > > this will switch to old SYNC printk() mode should such a lockup ever
> > > > happen, which is a giant advantage over any other implementation; doing
> > > > wake_up_process() within the 'we can detect recursive printk() here'
> > > > gives us better control.
> > > > 
> > > > why
> > > >   printk()->IRQ->wake_up_process()->spin_dump()->printk()->IRQ->wake_up_process()->spin_dump()->printk()->IRQ...
> > > > is better?
> > > 
> > > What is IRQ?
> > 
> > this is how printk() can print the messages in async mode apart from
> > direct and wake_up_process() in vprintk_emit().
> 
> Do you mean IRQ work?

yes.

> Is there any reason why you don't put the wake_up_process() out of the
> critical section

I provided reasons already.

> with my suggestion, even though it can solve the infinite recuresion you worried about?

which is 'a static lock pointer in spin_dump()'? I don't think
this will fix recursive printks.



/* seems that for some reason my previous reply was not delivered. re-sending. */

	-ss