linux-kernel - Re: [GIT PULL pm-next] freezer: fix various bugs and simplify implementation

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Date:	Mon, 22 Aug 2011 20:50:59 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	arnd@...db.de, oleg@...hat.com, lizf@...fujitsu.com,
	paul@...lmenage.org, Matt Helsley <matthltc@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [GIT PULL pm-next] freezer: fix various bugs and simplify implementation

On Monday, August 22, 2011, Tejun Heo wrote:
> Hello, Rafael.
> 
> On Sun, Aug 21, 2011 at 08:03:14PM +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@...k.pl>
> > Subject: PM / Freezer: Move might_sleep() from try_to_freeze()
> > 
> > There are some code paths that call try_to_freeze() from interrupt
> > context, but doing so they know that the current process cannot
> > possible be freezing (e.g. during reboot on ARM).  However, the
> > recently added might_sleep() annotation in try_to_freeze()
> > triggers in those cases, making it look like there were bugs in
> > those places, which really isn't the case.
> > 
> > Therefore move might_sleep() from try_to_freeze() to
> > __refrigerator() so that it doesn't produce false positives.
> 
> Hmmm... I can't quite agree with this change.  Some invocations of
> try_to_freeze() can be very difficult to trigger.  Freezing isn't a
> frequent operation after some try_to_freeze() can be buried in weird
> places.  might_sleep() is exactly to detect context bugs in these
> situations.  If a code path is called from both sleepable and
> unsleepable context and it knows that the latter wouldn't happen if
> the system is freezing, that code path should conditionalize
> invocation of try_to_freeze() based on its knowledge of context.  That
> way, all other normal cases get the might_sleep() protection and the
> peculiar logic in that code path is explicitly described - win win.
> 
> Can you please point me to where the problem was?

Apparently, during reboot on ARM try_to_freeze() is called via
do_signal() with interrupts disabled.

Thanks,
Rafael
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