On Tue, 27 Nov 2007 23:35:36 +0100, 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.
Please be aware DABR works fine if the same code runs just 1 (always) or 2 (sometimes) threads. It starts failing with too many threads running: $ ./dabr-lost TID 32725: DABR 0x1001279f NIP 0xfecf41c TID 32726: DABR 0x1001279f NIP 0xfecf41c TID 32725: hitting the variable variable found = -1, caught TID = 32725 TID 32726: hitting the variable variable found = -1, caught TID = 32726 The kernel bug did not get reproduced - increase THREADS. As I did not find any code in that kernel touching DABRX its value should not be dependent on the number of threads running. Regards, Lace _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
