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Date:	Sun, 3 Jul 2011 10:21:37 +0200
From:	Florian Mickler <florian@...kler.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andrea Righi <andrea@...terlinux.com>, Len Brown <lenb@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI: fix acpi_power_off lockdep splat

On Sun, 3 Jul 2011 08:58:41 +0200
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Saturday, July 02, 2011, Andrea Righi wrote:
> > Implement acpi_os_create_lock() as a C-preprocessor macro to assign
> > unique lock_class_key to dynamically allocated locks and suppress wrong
> > lockdep warnings.
> > 
> > This fixes:
> > https://bugzilla.kernel.org/show_bug.cgi?id=38152
> > 
> > Reported-by: Borislav Petkov <bp@...en8.de>
> > Signed-off-by: Andrea Righi <andrea@...terlinux.com>
> 
> So, how exactly does it work?

The spin_lock_init macro stringifies it's argument and uses that as a
name for the lock in the debugging.

By re-executing spin_lock_init (have not checked if that harms
anything, but it should be ok) in the _macro_ the key changes from
"lock" for all three locks to the actual argument
"&acpi_gbl_global_lock_pending_lock", "&acpi_gbl_gpe_lock" or
"&acpi_gbl_hardware_lock". 

Regards,
Flo

> > ---
> >  drivers/acpi/osl.c      |    2 +-
> >  include/acpi/acpiosxf.h |   12 +++++++++++-
> >  2 files changed, 12 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> > index 52ca964..2a67602 100644
> > --- a/drivers/acpi/osl.c
> > +++ b/drivers/acpi/osl.c
> > @@ -1336,7 +1336,7 @@ EXPORT_SYMBOL(acpi_resources_are_enforced);
> >   * Create and initialize a spinlock.
> >   */
> >  acpi_status
> > -acpi_os_create_lock(acpi_spinlock *out_handle)
> > +__acpi_os_create_lock(acpi_spinlock *out_handle)
> >  {
> >  	spinlock_t *lock;
> >  
> > diff --git a/include/acpi/acpiosxf.h b/include/acpi/acpiosxf.h
> > index a756bc8..4a0385d 100644
> > --- a/include/acpi/acpiosxf.h
> > +++ b/include/acpi/acpiosxf.h
> > @@ -99,7 +99,17 @@ acpi_os_table_override(struct acpi_table_header *existing_table,
> >   * Spinlock primitives
> >   */
> >  acpi_status
> > -acpi_os_create_lock(acpi_spinlock *out_handle);
> > +__acpi_os_create_lock(acpi_spinlock *out_handle);
> > +
> > +#define acpi_os_create_lock(__handle)			\
> > +({							\
> > +	acpi_status ret;				\
> > +							\
> > +	ret = __acpi_os_create_lock(__handle);		\
> > +	if (ret == AE_OK)				\
> > +		spin_lock_init(*(__handle));		\
> 
> It seems that spin_lock_init() has already been done on *__handle, right?
> 
> > +	ret;						\
> > +})
> >  
> >  void acpi_os_delete_lock(acpi_spinlock handle);
> 
> Rafael
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