mutexes and preemption

[Sebastian Seifert <lathander-Mmb7MZpHnFY@public.gmane.org>]

Hello,

some vital information first: I'm using kernel 2.6.3-mm4 with DSDT in ramdisk
patch applied, preemption is enabled, SMP disabled. 

I'm currently debugging the DSDT of my laptop (Benq Joybook 5000). Some ACPI
method calls seem to be failing because of double acquisition of a mutex. One
reproducible way to trigger the problem is to read the ac adapter's state.  My
syslog looks like this (I set debug_level to 31 and added printks in
exoparg?.c):

Mar  2 23:03:10 tenshi kernel: Execute Method: [\_SB_.AC__._PSR] (Node dff60f88)
Mar  2 23:03:10 tenshi kernel: AML_ACQUIRE_OP on [MUT1] by thread 1370 (55A)
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0178 [2016] acpi_ec_read          : Read [08] from address [92]
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0178 [2022] acpi_ec_read          : Read [30] from address [9c]
Mar  2 23:03:10 tenshi kernel: AML_RELEASE_OP on [MUT1] by thread 1370 (55A)
Mar  2 23:03:10 tenshi kernel: exregion-0294 [2030] ex_system_io_space_han: system_iO 1 (8 width) Address=00000000000000B3
Mar  2 23:03:10 tenshi kernel: exregion-0294 [2030] ex_system_io_space_han: system_iO 1 (8 width) Address=00000000000000B2
Mar  2 23:03:10 tenshi kernel:   evmisc-0121 [2021] ev_queue_notify_reques: Dispatching Notify(81) on node dff61ca8
Mar  2 23:03:10 tenshi kernel:   evmisc-0137 [2021] ev_queue_notify_reques: Notify value: Status Change
Mar  2 23:03:10 tenshi kernel: Execute Method: [\_TZ_.THZN._TMP] (Node dff61c48)
Mar  2 23:03:10 tenshi kernel: AML_ACQUIRE_OP on [MUT1] by thread 1370 (55A)
Mar  2 23:03:10 tenshi kernel: AML_ACQUIRE_OP on [MUT1] by thread 3 (3)
Mar  2 23:03:10 tenshi kernel:      osl-0909 [2049] os_wait_semaphore     : Failed to acquire semaphore[dffd8680|1|0], AE_TIME
Mar  2 23:03:10 tenshi kernel:      osl-0909 [2049] os_wait_semaphore     : Failed to acquire semaphore[dffd8680|1|36863], AE_TIME
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0178 [2054] acpi_ec_read          : Read [30] from address [9c]
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0178 [2054] acpi_ec_read          : Read [28] from address [9d]
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0178 [2054] acpi_ec_read          : Read [3c] from address [9e]
Mar  2 23:03:10 tenshi kernel: AML_RELEASE_OP on [MUT1] by thread 3 (3)
Mar  2 23:03:10 tenshi kernel:  exmutex-0264: *** Error: Thread 3 cannot release Mutex [MUT1] acquired by thread 55A
Mar  2 23:03:10 tenshi kernel:  psparse-1120: *** Error: Method execution failed [\_TZ_.THZN._TMP] (Node dff61c48), AE_AML_NOT_OWNER
Mar  2 23:03:10 tenshi kernel: acpi_utils-0256 [2036] acpi_evaluate_integer : Evaluate [\_TZ_.THZN._TMP]: AE_AML_NOT_OWNER
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0178 [2034] acpi_ec_read          : Read [28] from address [9d]
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0230 [2036] acpi_ec_write         : Wrote [28] to address [9d]
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0178 [2045] acpi_ec_read          : Read [3c] from address [9e]
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0230 [2050] acpi_ec_write         : Wrote [3c] to address [9e]
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0178 [2058] acpi_ec_read          : Read [32] from address [a0]
Mar  2 23:03:10 tenshi kernel:  acpi_ec-0230 [2063] acpi_ec_write         : Wrote [28] to address [a0]
Mar  2 23:03:10 tenshi kernel: AML_RELEASE_OP on [MUT1] by thread 1370 (55A)
Mar  2 23:03:10 tenshi kernel: exregion-0372 [2072] ex_pci_config_space_ha: pci_config 0 (8) Seg(0000) Bus(0000) Dev(001f) Func(0000) Reg(00a0)
Mar  2 23:03:10 tenshi kernel: exregion-0372 [2072] ex_pci_config_space_ha: pci_config 1 (8) Seg(0000) Bus(0000) Dev(001f) Func(0000) Reg(00a0)
Mar  2 23:03:10 tenshi kernel: acpi_utils-0267 [2054] acpi_evaluate_integer : Return value [1]

_PSR acquires MUT1, reads some registers, then releases it.  Then, it calls
some method CHGT (not indicated by debug output, but I know from the DSDT),
which possibly changes some temperature trigger values, and Notifies the
thermal zone.  Then, it calls some method STEV, which acquires MUT1, does
something, and releases it.

What seems to happen is that the Notify enqueues an event for later processing
by thread 3, an event daemon.  Then, during the execution of STEV, which has
acquired MUT1, thread 1370 (in above example syslog) becomes preempted (it
seems). The event handler runs and tries to process the notification. Which
involves reading the temperature by calling _TMP, which tries to acquire the
same mutex MUT1. At least that's my analysis. If I disable kernel preemption,
the second release of MUT1 by the running thread happens before the acquire by
thread 3 and no error happens.

Now, I'm not sure what that means. Is preemption in combination with ACPI
unsupported? Is it legal to schedule away from a thread that is holding an ACPI
mutex?  Or is the way the mutex is used inside my DSDT invalid?  The DSDT looks
good to my eye, the mutex is only held for some lines of code while accessing
the embedded controller. But I don't know much about ACPI and the assumptions
that are made.

Another problem I'm having is that the OS does not seem to execute the _REG
method of my embedded controller. I'm circumventing this problem by setting the
controller's activation flag to 1 all the time, and faking values in _STA
methods (which are called during initialization while there is no embedded
controller operation region yet). But shouldn't _REG be called when the
operation region becomes enabled?

Thanks in advance,
Sebastian

Some relevant parts of my DSDT: 
    Method (CHGT, 1, NotSerialized)
    {
        Store (Arg0, TMOD)
        If (LEqual (Arg0, 0x00))
        {
            Store (MTPB, CTPB)
            \_SB.GSMI (0x18)
            Sleep (0x64)
            Store (0x00, TRON)
            Store (CTTP, PTMP)
        }

        If (LEqual (Arg0, 0x02))
        {
            Store (BTPB, CTPB)
            Store (PASH, PTMP)
        }

        Notify (\_TZ.THZN, 0x81) 
    }

    Method (STEV, 1, NotSerialized)
    {
        CreateByteField (CTPB, 0x00, TPL0)
        CreateByteField (CTPB, 0x01, TPH0)
        [...lots of conditional Stores...]
        Acquire (\_SB.PCI0.LPCB.EC0.MUT1, 0x8FFF)
        Store (TMPL, \_SB.PCI0.LPCB.EC0.LTMP)
        Store (TMPH, \_SB.PCI0.LPCB.EC0.HTMP)
        Store (CFSP, \_SB.PCI0.LPCB.EC0.FANS)
        Release (\_SB.PCI0.LPCB.EC0.MUT1)
    }

	ThermalZone (THZN)
        {
            Method (_TMP, 0, Serialized)
            {
                If (ECON)
                {
                    Acquire (\_SB.PCI0.LPCB.EC0.MUT1, 0x8FFF)
                    Store (\_SB.PCI0.LPCB.EC0.CCPT, Local0)
                    Store (\_SB.PCI0.LPCB.EC0.LTMP, Local1)
                    Store (\_SB.PCI0.LPCB.EC0.HTMP, Local2)
                    Release (\_SB.PCI0.LPCB.EC0.MUT1)
                    If (LOr (LNot (LEqual (TMPL, Local1)), LNot (LEqual (TMPH, Local2))))
                    {
                        STEV (Local0)
                    }

                    Add (Local0, 0x0111, Local0)
                    Multiply (Local0, 0x0A, Local0)
                    Return (Local0)
                }
                Else
                {
                    Return (0x0C80)
                }
            }
	    [...]
        }
	[...]
	Device (AC) 
        {
	    [...]
            Method (_PSR, 0, NotSerialized)
            {
                If (LEqual (DFEC, 0x00))
                {
                    If (ECON)
                    {
                        Acquire (\_SB.PCI0.LPCB.EC0.MUT1, 0x8FFF)
                        Store (\_SB.PCI0.LPCB.EC0.ACST, Local0)
                        Store (\_SB.PCI0.LPCB.EC0.CCPT, Local1)
                        Release (\_SB.PCI0.LPCB.EC0.MUT1)

                        If (LEqual (Local0, 0x01))
                        {   
                            CHGT (0x00)
                            STEV (Local1)
                            Store (0x00, \_SB.PCI0.LPCB.C4C3)
                        }
                        Else
                        {
                            CHGT (0x02)
                            STEV (Local1)
                            Store (0x01, \_SB.PCI0.LPCB.C4C3)
                        }

                        Return (Local0)
                    }
                    Else
                    {
                        Return (One)
                    }
                }
                Else
                {
                    Return (One)
                }
		/* this seems to be bogus - never reached ??
                Store (0xA0, MLIN)
                Store (MLDT, Local0)
                If (LEqual (Local0, 0x77))
                {
                    Return (0x01)
                }

                Acquire (\_SB.PCI0.LPCB.EC0.MUT1, 0x8FFF)
                Store (\_SB.PCI0.LPCB.EC0.PBAC, Local0)
                Release (\_SB.PCI0.LPCB.EC0.MUT1)
                Return (Local0)
		*/
            }


-- 
"Gott ist tot."
	--Nietzsche
"Nietzsche ist tot."
	--Gott


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