linux-kernel - Re: [PATCH v2] PM/Memory-hotplug: Avoid task freezing failures

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Message-ID: <20111116184157.GA25497@google.com>
Date:	Wed, 16 Nov 2011 10:41:57 -0800
From:	Tejun Heo <tj@...nel.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	rjw@...k.pl, pavel@....cz, lenb@...nel.org, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v2] PM/Memory-hotplug: Avoid task freezing failures

Hello,

On Wed, Nov 16, 2011 at 11:54:04PM +0530, Srivatsa S. Bhat wrote:
> Ok, so by "proper solution", are you referring to a totally different
> method (than grabbing pm_mutex) to implement mutual exclusion between
> subsystems and suspend/hibernation, something like the suspend blockers
> stuff and friends?
> Or are you hinting at just the existing code itself being fixed more
> properly than what this patch does, to avoid having side effects like
> you pointed out?

Oh, nothing fancy.  Just something w/o busy looping would be fine.
The stinking thing is we don't have mutex_lock_freezable().  Lack of
proper freezable interface seems to be a continuing problem and I'm
not sure what the proper solution should be at this point.  Maybe we
should promote freezable to a proper task state.  Maybe freezable
kthread is a bad idea to begin with.  Maybe instead of removing
freezable_with_signal() we should make that default, that way,
freezable can hitch on the pending signal handling (this creates
another set of problems tho - ie. who's responsible for clearing
TIF_SIGPENDING?).  I don't know.

Maybe just throw in msleep(10) there with fat ugly comment explaining
why the hack is necessary?

Thanks.

-- 
tejun
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