Messages in this thread | | | Date | Thu, 04 Oct 2007 21:08:42 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: race with page_referenced_one->ptep_test_and_clear_young and pagetable setup/pulldown |
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Andrew Morton wrote: > y'know, I think I think it's been several years since I saw a report of an > honest to goodness, genuine SMP race in core kernel. We used to be > infested by them, but the term has fallen into disuse. Interesting, but > OT. >
I was a bit surprised to find myself typing it too. I guess it could also be a preempt race, which has been a bit more common. Anyway, its a deliberately unlocked access to the pagetable structure, so not terribly surprising.
>> It seems to me that there are a few ways to fix this: >> >> 1. Use asm-generic/pgtable.h when CONFIG_PARAVIRT is enabled. This >> will clearly work, but is pretty blunt. >> 2. Make test_and_clear_pte_flags a new paravirt-op, which can be >> implemented in Xen as a hypercall, and as a raw test_and_clear_bit >> for everyone else. The downside is adding yet another pv-op. >> 3. Restructure the pagetable setup code so that the mm is not added >> to the prio tree until after arch_dup_mmap has been called (and >> the converse for exit_mmap). This is arguably cleaner, but I >> haven't looked to see how much trouble this would be. >> >> Thoughts anyone? Does making the pagetables visible "early" cause >> problems for anyone else? >> > > I expect that 2) has the maximum niceness*suitable-for-2.6.23 product. >
OK, I'll whip a patch together.
> That's if you actually care much about kernel.org major releases - do many > people run kernel.org kernels on Xen?
Well, given that there hasn't been a Xen-capable kernel.org release yet, no... But we'll see what happens when .23 goes out the door.
> If "not many" then we could perhaps > do something more elaborate for 2.6.23.1. But adding ever more pvops as > core kernel evolves was always expected. >
I think keep it simple for now; anything significant can wait for the brave new world of unified x86.
J
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