linux-kernel - Re: [RFC v2 3/6] kthread: warn on kill signal if not OOM

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Message-ID: <20140905232242.GE35667@core.coreip.homeip.net>
Date:	Fri, 5 Sep 2014 16:22:42 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Wu Zhangjin <falcon@...zu.com>, Takashi Iwai <tiwai@...e.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>, hare@...e.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Benjamin Poirier <bpoirier@...e.de>,
	Santosh Rastapur <santosh@...lsio.com>,
	Kay Sievers <kay@...y.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tim Gardner <tim.gardner@...onical.com>,
	Pierre Fersing <pierre-fersing@...rref.org>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	Casey Leedom <leedom@...lsio.com>,
	Hariprasad S <hariprasad@...lsio.com>,
	MPT-FusionLinux.pdl@...gotech.com,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC v2 3/6] kthread: warn on kill signal if not OOM

Hi Tejun,

On Sat, Sep 06, 2014 at 07:55:33AM +0900, Tejun Heo wrote:
> Hello, Dmitry.
> 
> On Fri, Sep 05, 2014 at 03:49:17PM -0700, Dmitry Torokhov wrote:
> > On Sat, Sep 06, 2014 at 07:31:39AM +0900, Tejun Heo wrote:
> > > On Sat, Sep 06, 2014 at 07:29:56AM +0900, Tejun Heo wrote:
> > > > It is for storage devices which always have guaranteed synchronous
> > > > probing on module load and well-defined probing order.
> > 
> > Agree about probing order (IIRC that is why we had to revert the
> > wholesale asynchronous probing a few years back) but totally disagree
> > about synchronous module loading.
> 
> I don't get it.  This is a behavior userland already depends on for
> boots.  What's there to agree or disagree?  This is just a fact that
> we can't do this w/o disturbing some userlands in a major way.

I am just expressing my disbelief that somebody relies on module loading
being synchronous with probing. Out of curiosity, do you have any
pointers?

> 
> > Anyway, I just posted a patch that I think preserves module loading
> > behavior and solves my issue with built-in modules. It does not help
> > Luis' issue though (but then I think the main problem is with systemd
> > being stupid there).
> 
> This sure can be worked around from userland side too by not imposing
> any timeout on module loading but that said for the same reasons that
> you've been arguing until now, I actually do think that it's kinda
> silly to make device probing synchronous to module loading at this
> time and age.  What we disagree on is not that we want to separate
> those waits.  It is about how to achieve it.

Well, there are separate things we want to solve. My main issue is not
with modules, but rather compiled-in drivers that stall kernel boot,
and these particular drivers are just fine if they are probed out of
bound.

> 
> > > To add a bit, if the argument here is that dependency on such behavior
> > > shouldn't exist and module loading and device probing should always be
> > > asynchronous, the right approach is implementing "synchronous_probing"
> > > flag not the other way around.  I actually wouldn't hate to see that
> > > change happening but whoever submits and routes such a change should
> > > be ready for a major shitstorm, I'm afraid.
> > 
> > I think we already had this storm and that is why here we have opt-in
> > behavior for the drivers.
> 
> It's a different shitstorm where we actively break bootings on some
> userlands.  Trust me.  That's gonna be a lot worse.

That did break bootings and that's why we reverted the wholesale async
probing.

Thanks.

-- 
Dmitry
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