[RFC PATCH] acpi/xen: Evaluate the _PDC properly (for 2.6.32, and 2.6.39)

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

I was trying to bring up an prototype box and it while it booted fine under
Linux, if I tried to do it under Dom0 with a modified Linux kernel it crashed.
By modified I mean it had the "xen/acpi: add xen acpi processor driver" patch in it.

I traced it down to a one line fix which fixed the issue.
It might make sense to back-port this to the 2.6.32 tree, and it _might_ fix
some problems folks had with the processor_xen module (CC-ed here). If you
see a similar stack trace to the one outlined in the patch - then you might
be hitting this bug.

Anyhow, I am not that familiar with Linux ACPI parser or how the P states
are exposed - so it might be that this patch is completly bogus. Feedback
would be much appreciated.


commit 498adade0091900564e6a6bf06a0f793f09d4764
Author: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date:   Tue Jun 14 21:44:35 2011 -0400

    acpi/xen: Evaluate the _PDC properly.
    
    The call to evaluate the _PDC was passing in the wrong argument.
    
    Instead of passing in the acpi_handle it was passing in the structure
    that held the acpi_handle as the second member. This can cause
    the wrong evaluation on some machines ending up in trying to evaluate
    the _PDC and dereferencing the prefix node (which is not part of
    that structure) and causing a NULL pointer exception.
    
    The results after running with this patch (and yes, there are no _PDC
    on this box):
    
    nsxfeval-0180 [2017820672] [4294967276] evaluate_object       : ----Entry
    nsxfeval-0359 [2017820672] [4294967276] evaluate_object       : ----Exit- ****Exception****: AE_BAD_PARAMETER
    processor_core-0306 [2017820672] [4294967275] processor_eval_pdc    : Could not evaluate _PDC, using legacy perf. control.
    nsxfeval-0180 [2017820672] [4294967276] evaluate_object       : ----Entry
    nsxfeval-0263 [2017820672] [4294967276] evaluate_object       : pathname is [_PPC]
      nseval-0090 [2017820672] [4294967277] ns_evaluate           : ----Entry
     nsutils-0707 [2017820672] [4294967278] ns_get_node           : ----Entry ffffffff8173d637
     nsutils-0391 [2017820672] [4294967279] ns_internalize_name   : ----Entry
     nsutils-0280 [2017820672] [4294967280] ns_build_internal_name: ----Entry
    
    Without the patch (I enabled tracing here so there are more details,
    note the prefix scope):
    
    nsxfeval-0180 [2017820672] [4294967276] evaluate_object       : ----Entry
      utcopy-0641 [2017820672] [4294967277] ut_copy_eobject_to_iob: ----Entry
      utcopy-0459 [2017820672] [4294967278] ut_copy_esimple_to_isi: ----Entry
    utobject-0097 [2017820672] [4294967279] ut_create_internal_obj: ----Entry Buffer
    utobject-0385 [2017820672] [4294967280] ut_allocate_object_des: ----Entry
    utobject-0401 [2017820672] [4294967280] ut_allocate_object_des: ffff8800779748b8 Size 48
    utobject-0403 [2017820672] [4294967280] ut_allocate_object_des: ----Exit- ffff8800779748b8
    utobject-0146 [2017820672] [4294967279] ut_create_internal_obj: ----Exit- ffff8800779748b8
      utcopy-0552 [2017820672] [4294967278] ut_copy_esimple_to_isi: ----Exit- AE_OK
      utcopy-0656 [2017820672] [4294967277] ut_copy_eobject_to_iob: ----Exit- AE_OK
    nsxfeval-0263 [2017820672] [4294967276] evaluate_object       : pathname is [_PDC]
      nseval-0090 [2017820672] [4294967277] ns_evaluate           : ----Entry
     nsutils-0707 [2017820672] [4294967278] ns_get_node           : ----Entry ffffffff81733097
     nsutils-0391 [2017820672] [4294967279] ns_internalize_name   : ----Entry
     nsutils-0280 [2017820672] [4294967280] ns_build_internal_name: ----Entry
     nsutils-0363 [2017820672] [4294967280] ns_build_internal_name: Returning [ffff880069151ef0] (rel) "_PDC"
     nsutils-0366 [2017820672] [4294967280] ns_build_internal_name: ----Exit- AE_OK
     nsutils-0419 [2017820672] [4294967279] ns_internalize_name   : ----Exit- AE_OK
     utmutex-0255 [2017820672] [4294967278] ut_acquire_mutex      : Thread 2017820672 attempting to acquire Mutex [ACPI_MTX_Namespace]
         osl-0973 [2017820672] [4294967278] os_wait_semaphore     : Waiting for semaphore[ffff88007f004280|1|65535]
         osl-0992 [2017820672] [4294967278] os_wait_semaphore     : Acquired semaphore[ffff88007f004280|1|65535] utmutex-0263 [2017820672] [4294967278] ut_acquire_mutex      : Thread 2017820672 acquired Mutex [ACPI_MTX_Namespace]
    nsaccess-0301 [2017820672] [4294967279] ns_lookup             : ----Entry
     nsutils-0663 [2017820672] [4294967280] ns_opens_scope        : ----Entry Untyped
     nsutils-0673 [2017820672] [4294967280] ns_opens_scope        : ----Exit- 0000000000000000
    nsaccess-0398 [2017820672] [4294967279] ns_lookup             : Searching relative to prefix scope [ÿÿÿÿ] (ffff880069163800)
    nsaccess-0510 [2017820672] [4294967279] ns_lookup             : Simple Pathname (1 segment, Flags=2)
      nsdump-0087 [2017820672] [4294967279] ns_print_pathname     : [_PDC]
    nssearch-0297 [2017820672] [4294967280] ns_search_and_enter   : ----Entry
    nssearch-0102 [2017820672] [4294967281] ns_search_one_scope   : ----Entry
     nsnames-0139 [2017820672] [4294967282] ns_get_external_pathna: ----Entry ffff880069163800
    BUG: unable to handle kernel NULL pointer dereference at 0000000000000418
    IP: [<ffffffff8129266f>] acpi_ns_get_pathname_length+0x1f/0x68
    .. snip..
    Pid: 1, comm: swapper Not tainted 2.6.39.1-00221-gbb09547 #1 Intel Corporation S2600CP/S2600CP
    .. snip..
    Call Trace:
     [<ffffffff81292905>] acpi_ns_get_external_pathname+0x38/0x137
     [<ffffffff81290a1f>] acpi_ns_search_one_scope+0x4b/0x1f5
     [<ffffffff81290cfa>] acpi_ns_search_and_enter+0x131/0x42f
     [<ffffffff81290310>] acpi_ns_lookup+0x4c8/0x6c9
     [<ffffffff812933e3>] acpi_ns_get_node+0xe8/0x16e
     [<ffffffff812920bf>] acpi_ns_evaluate+0x83/0x3b6
     [<ffffffff812916f7>] acpi_evaluate_object+0x1f9/0x35b
     [<ffffffff81123d7b>] ? kmem_cache_alloc_trace+0xa0/0xb0
     [<ffffffff814a4e35>] acpi_processor_set_pdc+0x1cc/0x226
     [<ffffffff814a5a1e>] xen_acpi_processor_add+0x45c/0x59d
    
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/drivers/acpi/processor_xen.c b/drivers/acpi/processor_xen.c
index 43760f8..db54525 100644
--- a/drivers/acpi/processor_xen.c
+++ b/drivers/acpi/processor_xen.c
@@ -311,7 +311,7 @@ static int __cpuinit xen_acpi_processor_add(struct acpi_device *device)
 	}
 
 	/* _PDC call should be done before doing anything else (if reqd.). */
-	acpi_processor_set_pdc(pr);
+	acpi_processor_set_pdc(pr->handle);
 
 #ifdef CONFIG_CPU_FREQ
 	xen_acpi_processor_ppc_has_changed(pr);