Messages in this thread Patch in this message | | | Subject | Re: [RFC][PATCH] linux-2.6.0-test2_mtrr-race-fix_A0 | From | Mark Haverkamp <> | Date | Wed, 06 Aug 2003 11:05:08 -0700 |
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On Wed, 2003-08-06 at 10:15, john stultz wrote: > On Wed, 2003-08-06 at 01:52, Mathias Fröhlich wrote: > > Hi, > > > > You should not remove the barrier past mtrr change. If you do that, it is > > possible that cpu's run with inconsistent mtrrs. This can have bad > > sideeffects since at least the cache snooping protocol used by intel uses > > assumptions about the cachability of memory regions. Those information about > > the cachability is also taken from the mtrrs as far as I remember. > > This intel cpu developer manual, which documented the early PII and PPro > > chips, recommended this algorithm. Since actual intel cpus use the same old > > cpu to chipset bus protocol, this old documentation most propably still > > applies. > > Hmm. I should dig up that doc. Its a little hazy in my mind, but I think > I understand your description. I'm glad you caught this, as I can't > imagine the subtle bugs that might have popped up. > > Well, let me look at it again and see if I can come up with a proper > fix. > > Thanks for the knowledgeable feedback and sanity checking! > -john
I added an extra sync up from the caller after the last gate change so it is the last one to touch the automatic data.
Mark.
===== arch/i386/kernel/cpu/mtrr/main.c 1.29 vs edited ===== --- 1.29/arch/i386/kernel/cpu/mtrr/main.c Tue Jul 15 10:08:48 2003 +++ edited/arch/i386/kernel/cpu/mtrr/main.c Wed Aug 6 10:46:00 2003 @@ -169,6 +169,7 @@ cpu_relax(); barrier(); } + atomic_dec(&data->count); local_irq_restore(flags); } @@ -256,8 +257,18 @@ cpu_relax(); barrier(); } - local_irq_restore(flags); + atomic_set(&data.count, num_booting_cpus() - 1); atomic_set(&data.gate,0); + + /* + * Wait here for everyone to have seen the gate change + * So we're the last ones to touch 'data' + */ + while(atomic_read(&data.count)) { + cpu_relax(); + barrier(); + } + local_irq_restore(flags); } /**
-- Mark Haverkamp <markh@osdl.org>
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