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

[Rafael J. Wysocki]

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@xxxxxxx>
> > 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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