> From: linux-acpi-ow...@vger.kernel.org
> [mailto:linux-acpi-ow...@vger.kernel.org] On Behalf Of Zheng, Lv
> Sent: Friday, July 26, 2013 9:54 AM
> To: Rafael J. Wysocki
> Cc: Wysocki, Rafael J; Brown, Len; linux-kernel@vger.kernel.org;
> linux-a...@vger.kernel.org
> Subject: RE: [PATCH 06/13] ACPI/IPMI: Add reference counting for ACPI
> operation region handlers
>
> > From: Rafael J. Wysocki [mailto:r...@sisk.pl]
> > Sent: Friday, July 26, 2013 5:29 AM
> >
> > On Tuesday, July 23, 2013 04:09:43 PM Lv Zheng wrote:
> > > This patch adds reference couting for ACPI operation region handlers
> > > to fix races caused by the ACPICA address space callback invocations.
> > >
> > > ACPICA address space callback invocation is not suitable for Linux
> > > CONFIG_MODULE=y execution environment.
> >
> > Actually, can you please explain to me what *exactly* the problem is?
>
> OK. I'll add race explanations in the next revision.
>
> The problem is there is no "lock" held inside ACPICA for invoking operation
> region handlers.
> Thus races happens between the acpi_remove/install_address_space_handler
> and the handler/setup callbacks.
This seems not a good explanation of the intent of this patch.
I think the intent is here in the patch description:
1. It acts as a barrier for operation region callbacks - no callback will
happen after acpi_unregister_region().
2. acpi_unregister_region() is safe to be called in moudle->exit()
functions.
Hmm, maybe I need to re-order the patch description for this patch.
Thanks for commenting.
Best regards
-Lv
>
> This is correct per ACPI specification.
> As if there is interpreter locks held for invoking operation region handlers,
> the
> timeout implemented inside the operation region handlers will make all locking
> facilities (Acquire or Sleep,...) timed out.
> Please refer to ACPI specification "5.5.2 Control Method Execution":
> Interpretation of a Control Method is not preemptive, but it can block. When a
> control method does block, OSPM can initiate or continue the execution of a
> different control method. A control method can only assume that access to
> global objects is exclusive for any period the control method does not block.
>
> So it is pretty much likely that ACPI IO transfers are locked inside the
> operation
> region callback implementations.
> Using locking facility to protect the callback invocation will risk dead
> locks.
>
> Thanks
> -Lv
>
> > Rafael
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