Subject: Re: PPC upstream kernel ignored DABR bug

From: Geoff Levand <[email-masked]>
Date: Wed, 28 Nov 2007 14:59:36 -0800

Arnd Bergmann wrote:
> On Monday 26 November 2007, Jan Kratochvil wrote:
>> Hi,
>> 
>> this testcase:
>>         http://people.redhat.com/jkratoch/dabr-lost.c
>> 
>> reproduces a PPC DABR kernel bug.  The variable `variable' should not get
>> modified as the thread modifying it should be caught by its DABR:
>> 
>> $ ./dabr-lost
>> TID 30914: DABR 0x10012a77 NIP 0x80f6ebb318
>> TID 30915: DABR 0x10012a77 NIP 0x80f6ebb318
>> TID 30916: DABR 0x10012a77 NIP 0x80f6ebb318
>> TID 30914: hitting the variable
>> TID 30915: hitting the variable
>> TID 30916: hitting the variable
>> variable found = 30916, caught TID = 30914
>> TID 30916: DABR 0x10012a77
>> Variable got modified by a thread which has DABR still set!
>> 
> 
> This sounds like a bug recently reported by Uli Weigand. BenH
> said he'd take a look, but it probably fell under the table.
> The problem found by Uli is that on certain processors (Cell/B.E.
> in his case), the DABRX register needs to be set in order for
> the DABR to take effect.

Just as a note, the PS3's lv1_set_dabr(), which we used for
ppc_md.set_dabr sets up both the DABRX and DABR registers.

-Geoff